view src/os/linux/vm/os_linux.cpp @ 5761:b86041bd7b99

8010722: assert: failed: heap size is too big for compressed oops Summary: Use conservative assumptions of required alignment for the various garbage collector components into account when determining the maximum heap size that supports compressed oops. Using this conservative value avoids several circular dependencies in the calculation. Reviewed-by: stefank, dholmes
author tschatzl
date Tue, 18 Apr 2017 06:37:32 +0100
parents 124fc080dc67
children 8745b05c4772
line wrap: on
line source
/*
 * Copyright (c) 1999, 2015, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 *
 */

// no precompiled headers
#include "classfile/classLoader.hpp"
#include "classfile/systemDictionary.hpp"
#include "classfile/vmSymbols.hpp"
#include "code/icBuffer.hpp"
#include "code/vtableStubs.hpp"
#include "compiler/compileBroker.hpp"
#include "interpreter/interpreter.hpp"
#include "jvm_linux.h"
#include "memory/allocation.inline.hpp"
#include "memory/filemap.hpp"
#include "mutex_linux.inline.hpp"
#include "oops/oop.inline.hpp"
#include "os_share_linux.hpp"
#include "prims/jniFastGetField.hpp"
#include "prims/jvm.h"
#include "prims/jvm_misc.hpp"
#include "runtime/arguments.hpp"
#include "runtime/extendedPC.hpp"
#include "runtime/globals.hpp"
#include "runtime/interfaceSupport.hpp"
#include "runtime/init.hpp"
#include "runtime/java.hpp"
#include "runtime/javaCalls.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/osThread.hpp"
#include "runtime/perfMemory.hpp"
#include "runtime/sharedRuntime.hpp"
#include "runtime/statSampler.hpp"
#include "runtime/stubRoutines.hpp"
#include "runtime/threadCritical.hpp"
#include "runtime/timer.hpp"
#include "services/attachListener.hpp"
#include "services/memTracker.hpp"
#include "services/runtimeService.hpp"
#include "thread_linux.inline.hpp"
#include "utilities/decoder.hpp"
#include "utilities/defaultStream.hpp"
#include "utilities/events.hpp"
#include "utilities/elfFile.hpp"
#include "utilities/growableArray.hpp"
#include "utilities/vmError.hpp"
#ifdef TARGET_ARCH_x86
# include "assembler_x86.inline.hpp"
# include "nativeInst_x86.hpp"
#endif
#ifdef TARGET_ARCH_sparc
# include "assembler_sparc.inline.hpp"
# include "nativeInst_sparc.hpp"
#endif
#ifdef TARGET_ARCH_zero
# include "assembler_zero.inline.hpp"
# include "nativeInst_zero.hpp"
#endif
#ifdef TARGET_ARCH_arm
# include "assembler_arm.inline.hpp"
# include "nativeInst_arm.hpp"
#endif
#ifdef TARGET_ARCH_ppc
# include "assembler_ppc.inline.hpp"
# include "nativeInst_ppc.hpp"
#endif

// put OS-includes here
# include <sys/types.h>
# include <sys/mman.h>
# include <sys/stat.h>
# include <sys/select.h>
# include <pthread.h>
# include <signal.h>
# include <errno.h>
# include <dlfcn.h>
# include <stdio.h>
# include <unistd.h>
# include <sys/resource.h>
# include <pthread.h>
# include <sys/stat.h>
# include <sys/time.h>
# include <sys/times.h>
# include <sys/utsname.h>
# include <sys/socket.h>
# include <sys/wait.h>
# include <pwd.h>
# include <poll.h>
# include <semaphore.h>
# include <fcntl.h>
# include <string.h>
# include <syscall.h>
# include <sys/sysinfo.h>
# include <gnu/libc-version.h>
# include <sys/ipc.h>
# include <sys/shm.h>
# include <link.h>
# include <stdint.h>
# include <inttypes.h>
# include <sys/ioctl.h>

// if RUSAGE_THREAD for getrusage() has not been defined, do it here. The code calling
// getrusage() is prepared to handle the associated failure.
#ifndef RUSAGE_THREAD
#define RUSAGE_THREAD   (1)               /* only the calling thread */
#endif

#define MAX_PATH    (2 * K)

#define MAX_SECS 100000000

// for timer info max values which include all bits
#define ALL_64_BITS CONST64(0xFFFFFFFFFFFFFFFF)

#define LARGEPAGES_BIT (1 << 6)
////////////////////////////////////////////////////////////////////////////////
// global variables
julong os::Linux::_physical_memory = 0;

address   os::Linux::_initial_thread_stack_bottom = NULL;
uintptr_t os::Linux::_initial_thread_stack_size   = 0;

int (*os::Linux::_clock_gettime)(clockid_t, struct timespec *) = NULL;
int (*os::Linux::_pthread_getcpuclockid)(pthread_t, clockid_t *) = NULL;
Mutex* os::Linux::_createThread_lock = NULL;
pthread_t os::Linux::_main_thread;
int os::Linux::_page_size = -1;
const int os::Linux::_vm_default_page_size = (8 * K);
bool os::Linux::_is_floating_stack = false;
bool os::Linux::_is_NPTL = false;
bool os::Linux::_supports_fast_thread_cpu_time = false;
const char * os::Linux::_glibc_version = NULL;
const char * os::Linux::_libpthread_version = NULL;
pthread_condattr_t os::Linux::_condattr[1];

static jlong initial_time_count=0;

static int clock_tics_per_sec = 100;

// For diagnostics to print a message once. see run_periodic_checks
static sigset_t check_signal_done;
static bool check_signals = true;

static pid_t _initial_pid = 0;

/* Signal number used to suspend/resume a thread */

/* do not use any signal number less than SIGSEGV, see 4355769 */
static int SR_signum = SIGUSR2;
sigset_t SR_sigset;

/* Used to protect dlsym() calls */
static pthread_mutex_t dl_mutex;

// Declarations
static void unpackTime(timespec* absTime, bool isAbsolute, jlong time);

#ifdef JAVASE_EMBEDDED
class MemNotifyThread: public Thread {
  friend class VMStructs;
 public:
  virtual void run();

 private:
  static MemNotifyThread* _memnotify_thread;
  int _fd;

 public:

  // Constructor
  MemNotifyThread(int fd);

  // Tester
  bool is_memnotify_thread() const { return true; }

  // Printing
  char* name() const { return (char*)"Linux MemNotify Thread"; }

  // Returns the single instance of the MemNotifyThread
  static MemNotifyThread* memnotify_thread() { return _memnotify_thread; }

  // Create and start the single instance of MemNotifyThread
  static void start();
};
#endif // JAVASE_EMBEDDED

// utility functions

static int SR_initialize();
static int SR_finalize();

julong os::available_memory() {
  return Linux::available_memory();
}

julong os::Linux::available_memory() {
  // values in struct sysinfo are "unsigned long"
  struct sysinfo si;
  sysinfo(&si);

  return (julong)si.freeram * si.mem_unit;
}

julong os::physical_memory() {
  return Linux::physical_memory();
}

////////////////////////////////////////////////////////////////////////////////
// environment support

bool os::getenv(const char* name, char* buf, int len) {
  const char* val = ::getenv(name);
  if (val != NULL && strlen(val) < (size_t)len) {
    strcpy(buf, val);
    return true;
  }
  if (len > 0) buf[0] = 0;  // return a null string
  return false;
}


// Return true if user is running as root.

bool os::have_special_privileges() {
  static bool init = false;
  static bool privileges = false;
  if (!init) {
    privileges = (getuid() != geteuid()) || (getgid() != getegid());
    init = true;
  }
  return privileges;
}


#ifndef SYS_gettid
// i386: 224, ia64: 1105, amd64: 186, sparc 143
#ifdef __ia64__
#define SYS_gettid 1105
#elif __i386__
#define SYS_gettid 224
#elif __amd64__
#define SYS_gettid 186
#elif __sparc__
#define SYS_gettid 143
#else
#error define gettid for the arch
#endif
#endif

// Cpu architecture string
#if   defined(ZERO)
static char cpu_arch[] = ZERO_LIBARCH;
#elif defined(IA64)
static char cpu_arch[] = "ia64";
#elif defined(IA32)
static char cpu_arch[] = "i386";
#elif defined(AMD64)
static char cpu_arch[] = "amd64";
#elif defined(ARM)
static char cpu_arch[] = "arm";
#elif defined(PPC32)
static char cpu_arch[] = "ppc";
#elif defined(PPC64)
static char cpu_arch[] = "ppc64";
#elif defined(SPARC)
#  ifdef _LP64
static char cpu_arch[] = "sparcv9";
#  else
static char cpu_arch[] = "sparc";
#  endif
#else
#error Add appropriate cpu_arch setting
#endif


// pid_t gettid()
//
// Returns the kernel thread id of the currently running thread. Kernel
// thread id is used to access /proc.
//
// (Note that getpid() on LinuxThreads returns kernel thread id too; but
// on NPTL, it returns the same pid for all threads, as required by POSIX.)
//
pid_t os::Linux::gettid() {
  int rslt = syscall(SYS_gettid);
  if (rslt == -1) {
     // old kernel, no NPTL support
     return getpid();
  } else {
     return (pid_t)rslt;
  }
}

// Most versions of linux have a bug where the number of processors are
// determined by looking at the /proc file system.  In a chroot environment,
// the system call returns 1.  This causes the VM to act as if it is
// a single processor and elide locking (see is_MP() call).
static bool unsafe_chroot_detected = false;
static const char *unstable_chroot_error = "/proc file system not found.\n"
                     "Java may be unstable running multithreaded in a chroot "
                     "environment on Linux when /proc filesystem is not mounted.";

void os::Linux::initialize_system_info() {
  set_processor_count(sysconf(_SC_NPROCESSORS_CONF));
  if (processor_count() == 1) {
    pid_t pid = os::Linux::gettid();
    char fname[32];
    jio_snprintf(fname, sizeof(fname), "/proc/%d", pid);
    FILE *fp = fopen(fname, "r");
    if (fp == NULL) {
      unsafe_chroot_detected = true;
    } else {
      fclose(fp);
    }
  }
  _physical_memory = (julong)sysconf(_SC_PHYS_PAGES) * (julong)sysconf(_SC_PAGESIZE);
  assert(processor_count() > 0, "linux error");
}

void os::init_system_properties_values() {
//  char arch[12];
//  sysinfo(SI_ARCHITECTURE, arch, sizeof(arch));

  // The next steps are taken in the product version:
  //
  // Obtain the JAVA_HOME value from the location of libjvm[_g].so.
  // This library should be located at:
  // <JAVA_HOME>/jre/lib/<arch>/{client|server}/libjvm[_g].so.
  //
  // If "/jre/lib/" appears at the right place in the path, then we
  // assume libjvm[_g].so is installed in a JDK and we use this path.
  //
  // Otherwise exit with message: "Could not create the Java virtual machine."
  //
  // The following extra steps are taken in the debugging version:
  //
  // If "/jre/lib/" does NOT appear at the right place in the path
  // instead of exit check for $JAVA_HOME environment variable.
  //
  // If it is defined and we are able to locate $JAVA_HOME/jre/lib/<arch>,
  // then we append a fake suffix "hotspot/libjvm[_g].so" to this path so
  // it looks like libjvm[_g].so is installed there
  // <JAVA_HOME>/jre/lib/<arch>/hotspot/libjvm[_g].so.
  //
  // Otherwise exit.
  //
  // Important note: if the location of libjvm.so changes this
  // code needs to be changed accordingly.

  // The next few definitions allow the code to be verbatim:
#define malloc(n) (char*)NEW_C_HEAP_ARRAY(char, (n), mtInternal)
#define getenv(n) ::getenv(n)

/*
 * See ld(1):
 *      The linker uses the following search paths to locate required
 *      shared libraries:
 *        1: ...
 *        ...
 *        7: The default directories, normally /lib and /usr/lib.
 */
#if defined(AMD64) || defined(_LP64) && (defined(SPARC) || defined(PPC) || defined(S390))
#define DEFAULT_LIBPATH "/usr/lib64:/lib64:/lib:/usr/lib"
#else
#define DEFAULT_LIBPATH "/lib:/usr/lib"
#endif

#define EXTENSIONS_DIR  "/lib/ext"
#define ENDORSED_DIR    "/lib/endorsed"
#define REG_DIR         "/usr/java/packages"

  {
    /* sysclasspath, java_home, dll_dir */
    {
        char *home_path;
        char *dll_path;
        char *pslash;
        char buf[MAXPATHLEN];
        os::jvm_path(buf, sizeof(buf));

        // Found the full path to libjvm.so.
        // Now cut the path to <java_home>/jre if we can.
        *(strrchr(buf, '/')) = '\0';  /* get rid of /libjvm.so */
        pslash = strrchr(buf, '/');
        if (pslash != NULL)
            *pslash = '\0';           /* get rid of /{client|server|hotspot} */
        dll_path = malloc(strlen(buf) + 1);
        if (dll_path == NULL)
            return;
        strcpy(dll_path, buf);
        Arguments::set_dll_dir(dll_path);

        if (pslash != NULL) {
            pslash = strrchr(buf, '/');
            if (pslash != NULL) {
                *pslash = '\0';       /* get rid of /<arch> */
                pslash = strrchr(buf, '/');
                if (pslash != NULL)
                    *pslash = '\0';   /* get rid of /lib */
            }
        }

        home_path = malloc(strlen(buf) + 1);
        if (home_path == NULL)
            return;
        strcpy(home_path, buf);
        Arguments::set_java_home(home_path);

        if (!set_boot_path('/', ':'))
            return;
    }

    /*
     * Where to look for native libraries
     *
     * Note: Due to a legacy implementation, most of the library path
     * is set in the launcher.  This was to accomodate linking restrictions
     * on legacy Linux implementations (which are no longer supported).
     * Eventually, all the library path setting will be done here.
     *
     * However, to prevent the proliferation of improperly built native
     * libraries, the new path component /usr/java/packages is added here.
     * Eventually, all the library path setting will be done here.
     */
    {
        char *ld_library_path;

        /*
         * Construct the invariant part of ld_library_path. Note that the
         * space for the colon and the trailing null are provided by the
         * nulls included by the sizeof operator (so actually we allocate
         * a byte more than necessary).
         */
        ld_library_path = (char *) malloc(sizeof(REG_DIR) + sizeof("/lib/") +
            strlen(cpu_arch) + sizeof(DEFAULT_LIBPATH));
        sprintf(ld_library_path, REG_DIR "/lib/%s:" DEFAULT_LIBPATH, cpu_arch);

        /*
         * Get the user setting of LD_LIBRARY_PATH, and prepended it.  It
         * should always exist (until the legacy problem cited above is
         * addressed).
         */
        char *v = getenv("LD_LIBRARY_PATH");
        if (v != NULL) {
            char *t = ld_library_path;
            /* That's +1 for the colon and +1 for the trailing '\0' */
            ld_library_path = (char *) malloc(strlen(v) + 1 + strlen(t) + 1);
            sprintf(ld_library_path, "%s:%s", v, t);
        }
        Arguments::set_library_path(ld_library_path);
    }

    /*
     * Extensions directories.
     *
     * Note that the space for the colon and the trailing null are provided
     * by the nulls included by the sizeof operator (so actually one byte more
     * than necessary is allocated).
     */
    {
        char *buf = malloc(strlen(Arguments::get_java_home()) +
            sizeof(EXTENSIONS_DIR) + sizeof(REG_DIR) + sizeof(EXTENSIONS_DIR));
        sprintf(buf, "%s" EXTENSIONS_DIR ":" REG_DIR EXTENSIONS_DIR,
            Arguments::get_java_home());
        Arguments::set_ext_dirs(buf);
    }

    /* Endorsed standards default directory. */
    {
        char * buf;
        buf = malloc(strlen(Arguments::get_java_home()) + sizeof(ENDORSED_DIR));
        sprintf(buf, "%s" ENDORSED_DIR, Arguments::get_java_home());
        Arguments::set_endorsed_dirs(buf);
    }
  }

#undef malloc
#undef getenv
#undef EXTENSIONS_DIR
#undef ENDORSED_DIR

  // Done
  return;
}

////////////////////////////////////////////////////////////////////////////////
// breakpoint support

void os::breakpoint() {
  BREAKPOINT;
}

extern "C" void breakpoint() {
  // use debugger to set breakpoint here
}

////////////////////////////////////////////////////////////////////////////////
// signal support

debug_only(static bool signal_sets_initialized = false);
static sigset_t unblocked_sigs, vm_sigs, allowdebug_blocked_sigs;

bool os::Linux::is_sig_ignored(int sig) {
      struct sigaction oact;
      sigaction(sig, (struct sigaction*)NULL, &oact);
      void* ohlr = oact.sa_sigaction ? CAST_FROM_FN_PTR(void*,  oact.sa_sigaction)
                                     : CAST_FROM_FN_PTR(void*,  oact.sa_handler);
      if (ohlr == CAST_FROM_FN_PTR(void*, SIG_IGN))
           return true;
      else
           return false;
}

void os::Linux::signal_sets_init() {
  // Should also have an assertion stating we are still single-threaded.
  assert(!signal_sets_initialized, "Already initialized");
  // Fill in signals that are necessarily unblocked for all threads in
  // the VM. Currently, we unblock the following signals:
  // SHUTDOWN{1,2,3}_SIGNAL: for shutdown hooks support (unless over-ridden
  //                         by -Xrs (=ReduceSignalUsage));
  // BREAK_SIGNAL which is unblocked only by the VM thread and blocked by all
  // other threads. The "ReduceSignalUsage" boolean tells us not to alter
  // the dispositions or masks wrt these signals.
  // Programs embedding the VM that want to use the above signals for their
  // own purposes must, at this time, use the "-Xrs" option to prevent
  // interference with shutdown hooks and BREAK_SIGNAL thread dumping.
  // (See bug 4345157, and other related bugs).
  // In reality, though, unblocking these signals is really a nop, since
  // these signals are not blocked by default.
  sigemptyset(&unblocked_sigs);
  sigemptyset(&allowdebug_blocked_sigs);
  sigaddset(&unblocked_sigs, SIGILL);
  sigaddset(&unblocked_sigs, SIGSEGV);
  sigaddset(&unblocked_sigs, SIGBUS);
  sigaddset(&unblocked_sigs, SIGFPE);
#if defined(PPC64)
  sigaddset(&unblocked_sigs, SIGTRAP);
#endif
  sigaddset(&unblocked_sigs, SR_signum);

  if (!ReduceSignalUsage) {
   if (!os::Linux::is_sig_ignored(SHUTDOWN1_SIGNAL)) {
      sigaddset(&unblocked_sigs, SHUTDOWN1_SIGNAL);
      sigaddset(&allowdebug_blocked_sigs, SHUTDOWN1_SIGNAL);
   }
   if (!os::Linux::is_sig_ignored(SHUTDOWN2_SIGNAL)) {
      sigaddset(&unblocked_sigs, SHUTDOWN2_SIGNAL);
      sigaddset(&allowdebug_blocked_sigs, SHUTDOWN2_SIGNAL);
   }
   if (!os::Linux::is_sig_ignored(SHUTDOWN3_SIGNAL)) {
      sigaddset(&unblocked_sigs, SHUTDOWN3_SIGNAL);
      sigaddset(&allowdebug_blocked_sigs, SHUTDOWN3_SIGNAL);
   }
  }
  // Fill in signals that are blocked by all but the VM thread.
  sigemptyset(&vm_sigs);
  if (!ReduceSignalUsage)
    sigaddset(&vm_sigs, BREAK_SIGNAL);
  debug_only(signal_sets_initialized = true);

}

// These are signals that are unblocked while a thread is running Java.
// (For some reason, they get blocked by default.)
sigset_t* os::Linux::unblocked_signals() {
  assert(signal_sets_initialized, "Not initialized");
  return &unblocked_sigs;
}

// These are the signals that are blocked while a (non-VM) thread is
// running Java. Only the VM thread handles these signals.
sigset_t* os::Linux::vm_signals() {
  assert(signal_sets_initialized, "Not initialized");
  return &vm_sigs;
}

// These are signals that are blocked during cond_wait to allow debugger in
sigset_t* os::Linux::allowdebug_blocked_signals() {
  assert(signal_sets_initialized, "Not initialized");
  return &allowdebug_blocked_sigs;
}

void os::Linux::hotspot_sigmask(Thread* thread) {

  //Save caller's signal mask before setting VM signal mask
  sigset_t caller_sigmask;
  pthread_sigmask(SIG_BLOCK, NULL, &caller_sigmask);

  OSThread* osthread = thread->osthread();
  osthread->set_caller_sigmask(caller_sigmask);

  pthread_sigmask(SIG_UNBLOCK, os::Linux::unblocked_signals(), NULL);

  if (!ReduceSignalUsage) {
    if (thread->is_VM_thread()) {
      // Only the VM thread handles BREAK_SIGNAL ...
      pthread_sigmask(SIG_UNBLOCK, vm_signals(), NULL);
    } else {
      // ... all other threads block BREAK_SIGNAL
      pthread_sigmask(SIG_BLOCK, vm_signals(), NULL);
    }
  }
}

//////////////////////////////////////////////////////////////////////////////
// detecting pthread library

void os::Linux::libpthread_init() {
  // Save glibc and pthread version strings. Note that _CS_GNU_LIBC_VERSION
  // and _CS_GNU_LIBPTHREAD_VERSION are supported in glibc >= 2.3.2. Use a
  // generic name for earlier versions.
  // Define macros here so we can build HotSpot on old systems.
# ifndef _CS_GNU_LIBC_VERSION
# define _CS_GNU_LIBC_VERSION 2
# endif
# ifndef _CS_GNU_LIBPTHREAD_VERSION
# define _CS_GNU_LIBPTHREAD_VERSION 3
# endif

  size_t n = confstr(_CS_GNU_LIBC_VERSION, NULL, 0);
  if (n > 0) {
     char *str = (char *)malloc(n, mtInternal);
     confstr(_CS_GNU_LIBC_VERSION, str, n);
     os::Linux::set_glibc_version(str);
  } else {
     // _CS_GNU_LIBC_VERSION is not supported, try gnu_get_libc_version()
     static char _gnu_libc_version[32];
     jio_snprintf(_gnu_libc_version, sizeof(_gnu_libc_version),
              "glibc %s %s", gnu_get_libc_version(), gnu_get_libc_release());
     os::Linux::set_glibc_version(_gnu_libc_version);
  }

  n = confstr(_CS_GNU_LIBPTHREAD_VERSION, NULL, 0);
  if (n > 0) {
     char *str = (char *)malloc(n, mtInternal);
     confstr(_CS_GNU_LIBPTHREAD_VERSION, str, n);
     // Vanilla RH-9 (glibc 2.3.2) has a bug that confstr() always tells
     // us "NPTL-0.29" even we are running with LinuxThreads. Check if this
     // is the case. LinuxThreads has a hard limit on max number of threads.
     // So sysconf(_SC_THREAD_THREADS_MAX) will return a positive value.
     // On the other hand, NPTL does not have such a limit, sysconf()
     // will return -1 and errno is not changed. Check if it is really NPTL.
     if (strcmp(os::Linux::glibc_version(), "glibc 2.3.2") == 0 &&
         strstr(str, "NPTL") &&
         sysconf(_SC_THREAD_THREADS_MAX) > 0) {
       free(str);
       os::Linux::set_libpthread_version("linuxthreads");
     } else {
       os::Linux::set_libpthread_version(str);
     }
  } else {
    // glibc before 2.3.2 only has LinuxThreads.
    os::Linux::set_libpthread_version("linuxthreads");
  }

  if (strstr(libpthread_version(), "NPTL")) {
     os::Linux::set_is_NPTL();
  } else {
     os::Linux::set_is_LinuxThreads();
  }

  // LinuxThreads have two flavors: floating-stack mode, which allows variable
  // stack size; and fixed-stack mode. NPTL is always floating-stack.
  if (os::Linux::is_NPTL() || os::Linux::supports_variable_stack_size()) {
     os::Linux::set_is_floating_stack();
  }
}

/////////////////////////////////////////////////////////////////////////////
// thread stack

// Force Linux kernel to expand current thread stack. If "bottom" is close
// to the stack guard, caller should block all signals.
//
// MAP_GROWSDOWN:
//   A special mmap() flag that is used to implement thread stacks. It tells
//   kernel that the memory region should extend downwards when needed. This
//   allows early versions of LinuxThreads to only mmap the first few pages
//   when creating a new thread. Linux kernel will automatically expand thread
//   stack as needed (on page faults).
//
//   However, because the memory region of a MAP_GROWSDOWN stack can grow on
//   demand, if a page fault happens outside an already mapped MAP_GROWSDOWN
//   region, it's hard to tell if the fault is due to a legitimate stack
//   access or because of reading/writing non-exist memory (e.g. buffer
//   overrun). As a rule, if the fault happens below current stack pointer,
//   Linux kernel does not expand stack, instead a SIGSEGV is sent to the
//   application (see Linux kernel fault.c).
//
//   This Linux feature can cause SIGSEGV when VM bangs thread stack for
//   stack overflow detection.
//
//   Newer version of LinuxThreads (since glibc-2.2, or, RH-7.x) and NPTL do
//   not use this flag. However, the stack of initial thread is not created
//   by pthread, it is still MAP_GROWSDOWN. Also it's possible (though
//   unlikely) that user code can create a thread with MAP_GROWSDOWN stack
//   and then attach the thread to JVM.
//
// To get around the problem and allow stack banging on Linux, we need to
// manually expand thread stack after receiving the SIGSEGV.
//
// There are two ways to expand thread stack to address "bottom", we used
// both of them in JVM before 1.5:
//   1. adjust stack pointer first so that it is below "bottom", and then
//      touch "bottom"
//   2. mmap() the page in question
//
// Now alternate signal stack is gone, it's harder to use 2. For instance,
// if current sp is already near the lower end of page 101, and we need to
// call mmap() to map page 100, it is possible that part of the mmap() frame
// will be placed in page 100. When page 100 is mapped, it is zero-filled.
// That will destroy the mmap() frame and cause VM to crash.
//
// The following code works by adjusting sp first, then accessing the "bottom"
// page to force a page fault. Linux kernel will then automatically expand the
// stack mapping.
//
// _expand_stack_to() assumes its frame size is less than page size, which
// should always be true if the function is not inlined.

#if __GNUC__ < 3    // gcc 2.x does not support noinline attribute
#define NOINLINE
#else
#define NOINLINE __attribute__ ((noinline))
#endif

static void _expand_stack_to(address bottom) NOINLINE;

static void _expand_stack_to(address bottom) {
  address sp;
  size_t size;
  volatile char *p;

  // Adjust bottom to point to the largest address within the same page, it
  // gives us a one-page buffer if alloca() allocates slightly more memory.
  bottom = (address)align_size_down((uintptr_t)bottom, os::Linux::page_size());
  bottom += os::Linux::page_size() - 1;

  // sp might be slightly above current stack pointer; if that's the case, we
  // will alloca() a little more space than necessary, which is OK. Don't use
  // os::current_stack_pointer(), as its result can be slightly below current
  // stack pointer, causing us to not alloca enough to reach "bottom".
  sp = (address)&sp;

  if (sp > bottom) {
    size = sp - bottom;
    p = (volatile char *)alloca(size);
    assert(p != NULL && p <= (volatile char *)bottom, "alloca problem?");
    p[0] = '\0';
  }
}

bool os::Linux::manually_expand_stack(JavaThread * t, address addr) {
  assert(t!=NULL, "just checking");
  assert(t->osthread()->expanding_stack(), "expand should be set");
  assert(t->stack_base() != NULL, "stack_base was not initialized");

  if (addr <  t->stack_base() && addr >= t->stack_yellow_zone_base()) {
    sigset_t mask_all, old_sigset;
    sigfillset(&mask_all);
    pthread_sigmask(SIG_SETMASK, &mask_all, &old_sigset);
    _expand_stack_to(addr);
    pthread_sigmask(SIG_SETMASK, &old_sigset, NULL);
    return true;
  }
  return false;
}

//////////////////////////////////////////////////////////////////////////////
// create new thread

static address highest_vm_reserved_address();

// check if it's safe to start a new thread
static bool _thread_safety_check(Thread* thread) {
  if (os::Linux::is_LinuxThreads() && !os::Linux::is_floating_stack()) {
    // Fixed stack LinuxThreads (SuSE Linux/x86, and some versions of Redhat)
    //   Heap is mmap'ed at lower end of memory space. Thread stacks are
    //   allocated (MAP_FIXED) from high address space. Every thread stack
    //   occupies a fixed size slot (usually 2Mbytes, but user can change
    //   it to other values if they rebuild LinuxThreads).
    //
    // Problem with MAP_FIXED is that mmap() can still succeed even part of
    // the memory region has already been mmap'ed. That means if we have too
    // many threads and/or very large heap, eventually thread stack will
    // collide with heap.
    //
    // Here we try to prevent heap/stack collision by comparing current
    // stack bottom with the highest address that has been mmap'ed by JVM
    // plus a safety margin for memory maps created by native code.
    //
    // This feature can be disabled by setting ThreadSafetyMargin to 0
    //
    if (ThreadSafetyMargin > 0) {
      address stack_bottom = os::current_stack_base() - os::current_stack_size();

      // not safe if our stack extends below the safety margin
      return stack_bottom - ThreadSafetyMargin >= highest_vm_reserved_address();
    } else {
      return true;
    }
  } else {
    // Floating stack LinuxThreads or NPTL:
    //   Unlike fixed stack LinuxThreads, thread stacks are not MAP_FIXED. When
    //   there's not enough space left, pthread_create() will fail. If we come
    //   here, that means enough space has been reserved for stack.
    return true;
  }
}

// Thread start routine for all newly created threads
static void *java_start(Thread *thread) {
  // Try to randomize the cache line index of hot stack frames.
  // This helps when threads of the same stack traces evict each other's
  // cache lines. The threads can be either from the same JVM instance, or
  // from different JVM instances. The benefit is especially true for
  // processors with hyperthreading technology.
  static int counter = 0;
  int pid = os::current_process_id();
  alloca(((pid ^ counter++) & 7) * 128);

  ThreadLocalStorage::set_thread(thread);

  OSThread* osthread = thread->osthread();
  Monitor* sync = osthread->startThread_lock();

  // non floating stack LinuxThreads needs extra check, see above
  if (!_thread_safety_check(thread)) {
    // notify parent thread
    MutexLockerEx ml(sync, Mutex::_no_safepoint_check_flag);
    osthread->set_state(ZOMBIE);
    sync->notify_all();
    return NULL;
  }

  // thread_id is kernel thread id (similar to Solaris LWP id)
  osthread->set_thread_id(os::Linux::gettid());

  if (UseNUMA) {
    int lgrp_id = os::numa_get_group_id();
    if (lgrp_id != -1) {
      thread->set_lgrp_id(lgrp_id);
    }
  }
  // initialize signal mask for this thread
  os::Linux::hotspot_sigmask(thread);

  // initialize floating point control register
  os::Linux::init_thread_fpu_state();

  // handshaking with parent thread
  {
    MutexLockerEx ml(sync, Mutex::_no_safepoint_check_flag);

    // notify parent thread
    osthread->set_state(INITIALIZED);
    sync->notify_all();

    // wait until os::start_thread()
    while (osthread->get_state() == INITIALIZED) {
      sync->wait(Mutex::_no_safepoint_check_flag);
    }
  }

  // call one more level start routine
  thread->run();

  return 0;
}

bool os::create_thread(Thread* thread, ThreadType thr_type, size_t stack_size) {
  assert(thread->osthread() == NULL, "caller responsible");

  // Allocate the OSThread object
  OSThread* osthread = new OSThread(NULL, NULL);
  if (osthread == NULL) {
    return false;
  }

  // set the correct thread state
  osthread->set_thread_type(thr_type);

  // Initial state is ALLOCATED but not INITIALIZED
  osthread->set_state(ALLOCATED);

  thread->set_osthread(osthread);

  // init thread attributes
  pthread_attr_t attr;
  pthread_attr_init(&attr);
  pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_DETACHED);

  // stack size
  if (os::Linux::supports_variable_stack_size()) {
    // calculate stack size if it's not specified by caller
    if (stack_size == 0) {
      stack_size = os::Linux::default_stack_size(thr_type);

      switch (thr_type) {
      case os::java_thread:
        // Java threads use ThreadStackSize which default value can be
        // changed with the flag -Xss
        assert (JavaThread::stack_size_at_create() > 0, "this should be set");
        stack_size = JavaThread::stack_size_at_create();
        break;
      case os::compiler_thread:
        if (CompilerThreadStackSize > 0) {
          stack_size = (size_t)(CompilerThreadStackSize * K);
          break;
        } // else fall through:
          // use VMThreadStackSize if CompilerThreadStackSize is not defined
      case os::vm_thread:
      case os::pgc_thread:
      case os::cgc_thread:
      case os::watcher_thread:
        if (VMThreadStackSize > 0) stack_size = (size_t)(VMThreadStackSize * K);
        break;
      }
    }

    stack_size = MAX2(stack_size, os::Linux::min_stack_allowed);
    pthread_attr_setstacksize(&attr, stack_size);
  } else {
    // let pthread_create() pick the default value.
  }

  // glibc guard page
  pthread_attr_setguardsize(&attr, os::Linux::default_guard_size(thr_type));

  ThreadState state;

  {
    // Serialize thread creation if we are running with fixed stack LinuxThreads
    bool lock = os::Linux::is_LinuxThreads() && !os::Linux::is_floating_stack();
    if (lock) {
      os::Linux::createThread_lock()->lock_without_safepoint_check();
    }

    pthread_t tid;
    int ret = pthread_create(&tid, &attr, (void* (*)(void*)) java_start, thread);

    pthread_attr_destroy(&attr);

    if (ret != 0) {
      if (PrintMiscellaneous && (Verbose || WizardMode)) {
        perror("pthread_create()");
      }
      // Need to clean up stuff we've allocated so far
      thread->set_osthread(NULL);
      delete osthread;
      if (lock) os::Linux::createThread_lock()->unlock();
      return false;
    }

    // Store pthread info into the OSThread
    osthread->set_pthread_id(tid);

    // Wait until child thread is either initialized or aborted
    {
      Monitor* sync_with_child = osthread->startThread_lock();
      MutexLockerEx ml(sync_with_child, Mutex::_no_safepoint_check_flag);
      while ((state = osthread->get_state()) == ALLOCATED) {
        sync_with_child->wait(Mutex::_no_safepoint_check_flag);
      }
    }

    if (lock) {
      os::Linux::createThread_lock()->unlock();
    }
  }

  // Aborted due to thread limit being reached
  if (state == ZOMBIE) {
      thread->set_osthread(NULL);
      delete osthread;
      return false;
  }

  // The thread is returned suspended (in state INITIALIZED),
  // and is started higher up in the call chain
  assert(state == INITIALIZED, "race condition");
  return true;
}

/////////////////////////////////////////////////////////////////////////////
// attach existing thread

// bootstrap the main thread
bool os::create_main_thread(JavaThread* thread) {
  assert(os::Linux::_main_thread == pthread_self(), "should be called inside main thread");
  return create_attached_thread(thread);
}

bool os::create_attached_thread(JavaThread* thread) {
#ifdef ASSERT
    thread->verify_not_published();
#endif

  // Allocate the OSThread object
  OSThread* osthread = new OSThread(NULL, NULL);

  if (osthread == NULL) {
    return false;
  }

  // Store pthread info into the OSThread
  osthread->set_thread_id(os::Linux::gettid());
  osthread->set_pthread_id(::pthread_self());

  // initialize floating point control register
  os::Linux::init_thread_fpu_state();

  // Initial thread state is RUNNABLE
  osthread->set_state(RUNNABLE);

  thread->set_osthread(osthread);

  if (UseNUMA) {
    int lgrp_id = os::numa_get_group_id();
    if (lgrp_id != -1) {
      thread->set_lgrp_id(lgrp_id);
    }
  }

  if (os::Linux::is_initial_thread()) {
    // If current thread is initial thread, its stack is mapped on demand,
    // see notes about MAP_GROWSDOWN. Here we try to force kernel to map
    // the entire stack region to avoid SEGV in stack banging.
    // It is also useful to get around the heap-stack-gap problem on SuSE
    // kernel (see 4821821 for details). We first expand stack to the top
    // of yellow zone, then enable stack yellow zone (order is significant,
    // enabling yellow zone first will crash JVM on SuSE Linux), so there
    // is no gap between the last two virtual memory regions.

    JavaThread *jt = (JavaThread *)thread;
    address addr = jt->stack_yellow_zone_base();
    assert(addr != NULL, "initialization problem?");
    assert(jt->stack_available(addr) > 0, "stack guard should not be enabled");

    osthread->set_expanding_stack();
    os::Linux::manually_expand_stack(jt, addr);
    osthread->clear_expanding_stack();
  }

  // initialize signal mask for this thread
  // and save the caller's signal mask
  os::Linux::hotspot_sigmask(thread);

  return true;
}

void os::pd_start_thread(Thread* thread) {
  OSThread * osthread = thread->osthread();
  assert(osthread->get_state() != INITIALIZED, "just checking");
  Monitor* sync_with_child = osthread->startThread_lock();
  MutexLockerEx ml(sync_with_child, Mutex::_no_safepoint_check_flag);
  sync_with_child->notify();
}

// Free Linux resources related to the OSThread
void os::free_thread(OSThread* osthread) {
  assert(osthread != NULL, "osthread not set");

  if (Thread::current()->osthread() == osthread) {
    // Restore caller's signal mask
    sigset_t sigmask = osthread->caller_sigmask();
    pthread_sigmask(SIG_SETMASK, &sigmask, NULL);
   }

  delete osthread;
}

//////////////////////////////////////////////////////////////////////////////
// thread local storage

// Restore the thread pointer if the destructor is called. This is in case
// someone from JNI code sets up a destructor with pthread_key_create to run
// detachCurrentThread on thread death. Unless we restore the thread pointer we
// will hang or crash. When detachCurrentThread is called the key will be set
// to null and we will not be called again. If detachCurrentThread is never
// called we could loop forever depending on the pthread implementation.
static void restore_thread_pointer(void* p) {
  Thread* thread = (Thread*) p;
  os::thread_local_storage_at_put(ThreadLocalStorage::thread_index(), thread);
}

int os::allocate_thread_local_storage() {
  pthread_key_t key;
  int rslt = pthread_key_create(&key, restore_thread_pointer);
  assert(rslt == 0, "cannot allocate thread local storage");
  return (int)key;
}

// Note: This is currently not used by VM, as we don't destroy TLS key
// on VM exit.
void os::free_thread_local_storage(int index) {
  int rslt = pthread_key_delete((pthread_key_t)index);
  assert(rslt == 0, "invalid index");
}

void os::thread_local_storage_at_put(int index, void* value) {
  int rslt = pthread_setspecific((pthread_key_t)index, value);
  assert(rslt == 0, "pthread_setspecific failed");
}

extern "C" Thread* get_thread() {
  return ThreadLocalStorage::thread();
}

//////////////////////////////////////////////////////////////////////////////
// initial thread

// Check if current thread is the initial thread, similar to Solaris thr_main.
bool os::Linux::is_initial_thread(void) {
  char dummy;
  // If called before init complete, thread stack bottom will be null.
  // Can be called if fatal error occurs before initialization.
  if (initial_thread_stack_bottom() == NULL) return false;
  assert(initial_thread_stack_bottom() != NULL &&
         initial_thread_stack_size()   != 0,
         "os::init did not locate initial thread's stack region");
  if ((address)&dummy >= initial_thread_stack_bottom() &&
      (address)&dummy < initial_thread_stack_bottom() + initial_thread_stack_size())
       return true;
  else return false;
}

// Find the virtual memory area that contains addr
static bool find_vma(address addr, address* vma_low, address* vma_high) {
  FILE *fp = fopen("/proc/self/maps", "r");
  if (fp) {
    address low, high;
    while (!feof(fp)) {
      if (fscanf(fp, "%p-%p", &low, &high) == 2) {
        if (low <= addr && addr < high) {
           if (vma_low)  *vma_low  = low;
           if (vma_high) *vma_high = high;
           fclose (fp);
           return true;
        }
      }
      for (;;) {
        int ch = fgetc(fp);
        if (ch == EOF || ch == (int)'\n') break;
      }
    }
    fclose(fp);
  }
  return false;
}

// Locate initial thread stack. This special handling of initial thread stack
// is needed because pthread_getattr_np() on most (all?) Linux distros returns
// bogus value for initial thread.
void os::Linux::capture_initial_stack(size_t max_size) {
  // stack size is the easy part, get it from RLIMIT_STACK
  size_t stack_size;
  struct rlimit rlim;
  getrlimit(RLIMIT_STACK, &rlim);
  stack_size = rlim.rlim_cur;

  // 6308388: a bug in ld.so will relocate its own .data section to the
  //   lower end of primordial stack; reduce ulimit -s value a little bit
  //   so we won't install guard page on ld.so's data section.
  stack_size -= 2 * page_size();

  // 4441425: avoid crash with "unlimited" stack size on SuSE 7.1 or Redhat
  //   7.1, in both cases we will get 2G in return value.
  // 4466587: glibc 2.2.x compiled w/o "--enable-kernel=2.4.0" (RH 7.0,
  //   SuSE 7.2, Debian) can not handle alternate signal stack correctly
  //   for initial thread if its stack size exceeds 6M. Cap it at 2M,
  //   in case other parts in glibc still assumes 2M max stack size.
  // FIXME: alt signal stack is gone, maybe we can relax this constraint?
#ifndef IA64
  if (stack_size > 2 * K * K) stack_size = 2 * K * K;
#else
  // Problem still exists RH7.2 (IA64 anyway) but 2MB is a little small
  if (stack_size > 4 * K * K) stack_size = 4 * K * K;
#endif

  // Try to figure out where the stack base (top) is. This is harder.
  //
  // When an application is started, glibc saves the initial stack pointer in
  // a global variable "__libc_stack_end", which is then used by system
  // libraries. __libc_stack_end should be pretty close to stack top. The
  // variable is available since the very early days. However, because it is
  // a private interface, it could disappear in the future.
  //
  // Linux kernel saves start_stack information in /proc/<pid>/stat. Similar
  // to __libc_stack_end, it is very close to stack top, but isn't the real
  // stack top. Note that /proc may not exist if VM is running as a chroot
  // program, so reading /proc/<pid>/stat could fail. Also the contents of
  // /proc/<pid>/stat could change in the future (though unlikely).
  //
  // We try __libc_stack_end first. If that doesn't work, look for
  // /proc/<pid>/stat. If neither of them works, we use current stack pointer
  // as a hint, which should work well in most cases.

  uintptr_t stack_start;

  // try __libc_stack_end first
  uintptr_t *p = (uintptr_t *)dlsym(RTLD_DEFAULT, "__libc_stack_end");
  if (p && *p) {
    stack_start = *p;
  } else {
    // see if we can get the start_stack field from /proc/self/stat
    FILE *fp;
    int pid;
    char state;
    int ppid;
    int pgrp;
    int session;
    int nr;
    int tpgrp;
    unsigned long flags;
    unsigned long minflt;
    unsigned long cminflt;
    unsigned long majflt;
    unsigned long cmajflt;
    unsigned long utime;
    unsigned long stime;
    long cutime;
    long cstime;
    long prio;
    long nice;
    long junk;
    long it_real;
    uintptr_t start;
    uintptr_t vsize;
    intptr_t rss;
    uintptr_t rsslim;
    uintptr_t scodes;
    uintptr_t ecode;
    int i;

    // Figure what the primordial thread stack base is. Code is inspired
    // by email from Hans Boehm. /proc/self/stat begins with current pid,
    // followed by command name surrounded by parentheses, state, etc.
    char stat[2048];
    int statlen;

    fp = fopen("/proc/self/stat", "r");
    if (fp) {
      statlen = fread(stat, 1, 2047, fp);
      stat[statlen] = '\0';
      fclose(fp);

      // Skip pid and the command string. Note that we could be dealing with
      // weird command names, e.g. user could decide to rename java launcher
      // to "java 1.4.2 :)", then the stat file would look like
      //                1234 (java 1.4.2 :)) R ... ...
      // We don't really need to know the command string, just find the last
      // occurrence of ")" and then start parsing from there. See bug 4726580.
      char * s = strrchr(stat, ')');

      i = 0;
      if (s) {
        // Skip blank chars
        do s++; while (isspace(*s));

#define _UFM UINTX_FORMAT
#define _DFM INTX_FORMAT

        /*                                     1   1   1   1   1   1   1   1   1   1   2   2    2    2    2    2    2    2    2 */
        /*              3  4  5  6  7  8   9   0   1   2   3   4   5   6   7   8   9   0   1    2    3    4    5    6    7    8 */
        i = sscanf(s, "%c %d %d %d %d %d %lu %lu %lu %lu %lu %lu %lu %ld %ld %ld %ld %ld %ld " _UFM _UFM _DFM _UFM _UFM _UFM _UFM,
             &state,          /* 3  %c  */
             &ppid,           /* 4  %d  */
             &pgrp,           /* 5  %d  */
             &session,        /* 6  %d  */
             &nr,             /* 7  %d  */
             &tpgrp,          /* 8  %d  */
             &flags,          /* 9  %lu  */
             &minflt,         /* 10 %lu  */
             &cminflt,        /* 11 %lu  */
             &majflt,         /* 12 %lu  */
             &cmajflt,        /* 13 %lu  */
             &utime,          /* 14 %lu  */
             &stime,          /* 15 %lu  */
             &cutime,         /* 16 %ld  */
             &cstime,         /* 17 %ld  */
             &prio,           /* 18 %ld  */
             &nice,           /* 19 %ld  */
             &junk,           /* 20 %ld  */
             &it_real,        /* 21 %ld  */
             &start,          /* 22 UINTX_FORMAT */
             &vsize,          /* 23 UINTX_FORMAT */
             &rss,            /* 24 INTX_FORMAT  */
             &rsslim,         /* 25 UINTX_FORMAT */
             &scodes,         /* 26 UINTX_FORMAT */
             &ecode,          /* 27 UINTX_FORMAT */
             &stack_start);   /* 28 UINTX_FORMAT */
      }

#undef _UFM
#undef _DFM

      if (i != 28 - 2) {
         assert(false, "Bad conversion from /proc/self/stat");
         // product mode - assume we are the initial thread, good luck in the
         // embedded case.
         warning("Can't detect initial thread stack location - bad conversion");
         stack_start = (uintptr_t) &rlim;
      }
    } else {
      // For some reason we can't open /proc/self/stat (for example, running on
      // FreeBSD with a Linux emulator, or inside chroot), this should work for
      // most cases, so don't abort:
      warning("Can't detect initial thread stack location - no /proc/self/stat");
      stack_start = (uintptr_t) &rlim;
    }
  }

  // Now we have a pointer (stack_start) very close to the stack top, the
  // next thing to do is to figure out the exact location of stack top. We
  // can find out the virtual memory area that contains stack_start by
  // reading /proc/self/maps, it should be the last vma in /proc/self/maps,
  // and its upper limit is the real stack top. (again, this would fail if
  // running inside chroot, because /proc may not exist.)

  uintptr_t stack_top;
  address low, high;
  if (find_vma((address)stack_start, &low, &high)) {
    // success, "high" is the true stack top. (ignore "low", because initial
    // thread stack grows on demand, its real bottom is high - RLIMIT_STACK.)
    stack_top = (uintptr_t)high;
  } else {
    // failed, likely because /proc/self/maps does not exist
    warning("Can't detect initial thread stack location - find_vma failed");
    // best effort: stack_start is normally within a few pages below the real
    // stack top, use it as stack top, and reduce stack size so we won't put
    // guard page outside stack.
    stack_top = stack_start;
    stack_size -= 16 * page_size();
  }

  // stack_top could be partially down the page so align it
  stack_top = align_size_up(stack_top, page_size());

  if (max_size && stack_size > max_size) {
     _initial_thread_stack_size = max_size;
  } else {
     _initial_thread_stack_size = stack_size;
  }

  _initial_thread_stack_size = align_size_down(_initial_thread_stack_size, page_size());
  _initial_thread_stack_bottom = (address)stack_top - _initial_thread_stack_size;
}

////////////////////////////////////////////////////////////////////////////////
// time support

// Time since start-up in seconds to a fine granularity.
// Used by VMSelfDestructTimer and the MemProfiler.
double os::elapsedTime() {

  return (double)(os::elapsed_counter()) * 0.000001;
}

jlong os::elapsed_counter() {
  timeval time;
  int status = gettimeofday(&time, NULL);
  return jlong(time.tv_sec) * 1000 * 1000 + jlong(time.tv_usec) - initial_time_count;
}

jlong os::elapsed_frequency() {
  return (1000 * 1000);
}

bool os::supports_vtime() { return true; }
bool os::enable_vtime()   { return false; }
bool os::vtime_enabled()  { return false; }

double os::elapsedVTime() {
  struct rusage usage;
  int retval = getrusage(RUSAGE_THREAD, &usage);
  if (retval == 0) {
    return (double) (usage.ru_utime.tv_sec + usage.ru_stime.tv_sec) + (double) (usage.ru_utime.tv_usec + usage.ru_stime.tv_usec) / (1000 * 1000);
  } else {
    // better than nothing, but not much
    return elapsedTime();
  }
}

jlong os::javaTimeMillis() {
  timeval time;
  int status = gettimeofday(&time, NULL);
  assert(status != -1, "linux error");
  return jlong(time.tv_sec) * 1000  +  jlong(time.tv_usec / 1000);
}

#ifndef CLOCK_MONOTONIC
#define CLOCK_MONOTONIC (1)
#endif

void os::Linux::clock_init() {
  // we do dlopen's in this particular order due to bug in linux
  // dynamical loader (see 6348968) leading to crash on exit
  void* handle = dlopen("librt.so.1", RTLD_LAZY);
  if (handle == NULL) {
    handle = dlopen("librt.so", RTLD_LAZY);
  }

  if (handle) {
    int (*clock_getres_func)(clockid_t, struct timespec*) =
           (int(*)(clockid_t, struct timespec*))dlsym(handle, "clock_getres");
    int (*clock_gettime_func)(clockid_t, struct timespec*) =
           (int(*)(clockid_t, struct timespec*))dlsym(handle, "clock_gettime");
    if (clock_getres_func && clock_gettime_func) {
      // See if monotonic clock is supported by the kernel. Note that some
      // early implementations simply return kernel jiffies (updated every
      // 1/100 or 1/1000 second). It would be bad to use such a low res clock
      // for nano time (though the monotonic property is still nice to have).
      // It's fixed in newer kernels, however clock_getres() still returns
      // 1/HZ. We check if clock_getres() works, but will ignore its reported
      // resolution for now. Hopefully as people move to new kernels, this
      // won't be a problem.
      struct timespec res;
      struct timespec tp;
      if (clock_getres_func (CLOCK_MONOTONIC, &res) == 0 &&
          clock_gettime_func(CLOCK_MONOTONIC, &tp)  == 0) {
        // yes, monotonic clock is supported
        _clock_gettime = clock_gettime_func;
        return;
      } else {
        // close librt if there is no monotonic clock
        dlclose(handle);
      }
    }
  }
  warning("No monotonic clock was available - timed services may " \
          "be adversely affected if the time-of-day clock changes");
}

#ifndef SYS_clock_getres

#if defined(IA32) || defined(AMD64)
#define SYS_clock_getres IA32_ONLY(266)  AMD64_ONLY(229)
#define sys_clock_getres(x,y)  ::syscall(SYS_clock_getres, x, y)
#else
#warning "SYS_clock_getres not defined for this platform, disabling fast_thread_cpu_time"
#define sys_clock_getres(x,y)  -1
#endif

#else
#define sys_clock_getres(x,y)  ::syscall(SYS_clock_getres, x, y)
#endif

void os::Linux::fast_thread_clock_init() {
  if (!UseLinuxPosixThreadCPUClocks) {
    return;
  }
  clockid_t clockid;
  struct timespec tp;
  int (*pthread_getcpuclockid_func)(pthread_t, clockid_t *) =
      (int(*)(pthread_t, clockid_t *)) dlsym(RTLD_DEFAULT, "pthread_getcpuclockid");

  // Switch to using fast clocks for thread cpu time if
  // the sys_clock_getres() returns 0 error code.
  // Note, that some kernels may support the current thread
  // clock (CLOCK_THREAD_CPUTIME_ID) but not the clocks
  // returned by the pthread_getcpuclockid().
  // If the fast Posix clocks are supported then the sys_clock_getres()
  // must return at least tp.tv_sec == 0 which means a resolution
  // better than 1 sec. This is extra check for reliability.

  if(pthread_getcpuclockid_func &&
     pthread_getcpuclockid_func(_main_thread, &clockid) == 0 &&
     sys_clock_getres(clockid, &tp) == 0 && tp.tv_sec == 0) {

    _supports_fast_thread_cpu_time = true;
    _pthread_getcpuclockid = pthread_getcpuclockid_func;
  }
}

jlong os::javaTimeNanos() {
  if (Linux::supports_monotonic_clock()) {
    struct timespec tp;
    int status = Linux::clock_gettime(CLOCK_MONOTONIC, &tp);
    assert(status == 0, "gettime error");
    jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) + jlong(tp.tv_nsec);
    return result;
  } else {
    timeval time;
    int status = gettimeofday(&time, NULL);
    assert(status != -1, "linux error");
    jlong usecs = jlong(time.tv_sec) * (1000 * 1000) + jlong(time.tv_usec);
    return 1000 * usecs;
  }
}

void os::javaTimeNanos_info(jvmtiTimerInfo *info_ptr) {
  if (Linux::supports_monotonic_clock()) {
    info_ptr->max_value = ALL_64_BITS;

    // CLOCK_MONOTONIC - amount of time since some arbitrary point in the past
    info_ptr->may_skip_backward = false;      // not subject to resetting or drifting
    info_ptr->may_skip_forward = false;       // not subject to resetting or drifting
  } else {
    // gettimeofday - based on time in seconds since the Epoch thus does not wrap
    info_ptr->max_value = ALL_64_BITS;

    // gettimeofday is a real time clock so it skips
    info_ptr->may_skip_backward = true;
    info_ptr->may_skip_forward = true;
  }

  info_ptr->kind = JVMTI_TIMER_ELAPSED;                // elapsed not CPU time
}

// Return the real, user, and system times in seconds from an
// arbitrary fixed point in the past.
bool os::getTimesSecs(double* process_real_time,
                      double* process_user_time,
                      double* process_system_time) {
  struct tms ticks;
  clock_t real_ticks = times(&ticks);

  if (real_ticks == (clock_t) (-1)) {
    return false;
  } else {
    double ticks_per_second = (double) clock_tics_per_sec;
    *process_user_time = ((double) ticks.tms_utime) / ticks_per_second;
    *process_system_time = ((double) ticks.tms_stime) / ticks_per_second;
    *process_real_time = ((double) real_ticks) / ticks_per_second;

    return true;
  }
}


char * os::local_time_string(char *buf, size_t buflen) {
  struct tm t;
  time_t long_time;
  time(&long_time);
  localtime_r(&long_time, &t);
  jio_snprintf(buf, buflen, "%d-%02d-%02d %02d:%02d:%02d",
               t.tm_year + 1900, t.tm_mon + 1, t.tm_mday,
               t.tm_hour, t.tm_min, t.tm_sec);
  return buf;
}

struct tm* os::localtime_pd(const time_t* clock, struct tm*  res) {
  return localtime_r(clock, res);
}

////////////////////////////////////////////////////////////////////////////////
// runtime exit support

// Note: os::shutdown() might be called very early during initialization, or
// called from signal handler. Before adding something to os::shutdown(), make
// sure it is async-safe and can handle partially initialized VM.
void os::shutdown() {

  // allow PerfMemory to attempt cleanup of any persistent resources
  perfMemory_exit();

  // needs to remove object in file system
  AttachListener::abort();

  // flush buffered output, finish log files
  ostream_abort();

  // Check for abort hook
  abort_hook_t abort_hook = Arguments::abort_hook();
  if (abort_hook != NULL) {
    abort_hook();
  }

}

// Note: os::abort() might be called very early during initialization, or
// called from signal handler. Before adding something to os::abort(), make
// sure it is async-safe and can handle partially initialized VM.
void os::abort(bool dump_core) {
  os::shutdown();
  if (dump_core) {
#ifndef PRODUCT
    fdStream out(defaultStream::output_fd());
    out.print_raw("Current thread is ");
    char buf[16];
    jio_snprintf(buf, sizeof(buf), UINTX_FORMAT, os::current_thread_id());
    out.print_raw_cr(buf);
    out.print_raw_cr("Dumping core ...");
#endif
    ::abort(); // dump core
  }

  ::exit(1);
}

// Die immediately, no exit hook, no abort hook, no cleanup.
void os::die() {
  // _exit() on LinuxThreads only kills current thread
  ::abort();
}


// This method is a copy of JDK's sysGetLastErrorString
// from src/solaris/hpi/src/system_md.c

size_t os::lasterror(char *buf, size_t len) {

  if (errno == 0)  return 0;

  const char *s = ::strerror(errno);
  size_t n = ::strlen(s);
  if (n >= len) {
    n = len - 1;
  }
  ::strncpy(buf, s, n);
  buf[n] = '\0';
  return n;
}

intx os::current_thread_id() { return (intx)pthread_self(); }
int os::current_process_id() {

  // Under the old linux thread library, linux gives each thread
  // its own process id. Because of this each thread will return
  // a different pid if this method were to return the result
  // of getpid(2). Linux provides no api that returns the pid
  // of the launcher thread for the vm. This implementation
  // returns a unique pid, the pid of the launcher thread
  // that starts the vm 'process'.

  // Under the NPTL, getpid() returns the same pid as the
  // launcher thread rather than a unique pid per thread.
  // Use gettid() if you want the old pre NPTL behaviour.

  // if you are looking for the result of a call to getpid() that
  // returns a unique pid for the calling thread, then look at the
  // OSThread::thread_id() method in osThread_linux.hpp file

  return (int)(_initial_pid ? _initial_pid : getpid());
}

// DLL functions

const char* os::dll_file_extension() { return ".so"; }

// This must be hard coded because it's the system's temporary
// directory not the java application's temp directory, ala java.io.tmpdir.
const char* os::get_temp_directory() { return "/tmp"; }

static bool file_exists(const char* filename) {
  struct stat statbuf;
  if (filename == NULL || strlen(filename) == 0) {
    return false;
  }
  return os::stat(filename, &statbuf) == 0;
}

void os::dll_build_name(char* buffer, size_t buflen,
                        const char* pname, const char* fname) {
  // Copied from libhpi
  const size_t pnamelen = pname ? strlen(pname) : 0;

  // Quietly truncate on buffer overflow.  Should be an error.
  if (pnamelen + strlen(fname) + 10 > (size_t) buflen) {
      *buffer = '\0';
      return;
  }

  if (pnamelen == 0) {
    snprintf(buffer, buflen, "lib%s.so", fname);
  } else if (strchr(pname, *os::path_separator()) != NULL) {
    int n;
    char** pelements = split_path(pname, &n);
    for (int i = 0 ; i < n ; i++) {
      // Really shouldn't be NULL, but check can't hurt
      if (pelements[i] == NULL || strlen(pelements[i]) == 0) {
        continue; // skip the empty path values
      }
      snprintf(buffer, buflen, "%s/lib%s.so", pelements[i], fname);
      if (file_exists(buffer)) {
        break;
      }
    }
    // release the storage
    for (int i = 0 ; i < n ; i++) {
      if (pelements[i] != NULL) {
        FREE_C_HEAP_ARRAY(char, pelements[i], mtInternal);
      }
    }
    if (pelements != NULL) {
      FREE_C_HEAP_ARRAY(char*, pelements, mtInternal);
    }
  } else {
    snprintf(buffer, buflen, "%s/lib%s.so", pname, fname);
  }
}

const char* os::get_current_directory(char *buf, int buflen) {
  return getcwd(buf, buflen);
}

// check if addr is inside libjvm[_g].so
bool os::address_is_in_vm(address addr) {
  static address libjvm_base_addr;
  Dl_info dlinfo;

  if (libjvm_base_addr == NULL) {
    if (dladdr(CAST_FROM_FN_PTR(void *, os::address_is_in_vm), &dlinfo) != 0) {
      libjvm_base_addr = (address)dlinfo.dli_fbase;
    }
    assert(libjvm_base_addr !=NULL, "Cannot obtain base address for libjvm");
  }

  if (dladdr((void *)addr, &dlinfo) != 0) {
    if (libjvm_base_addr == (address)dlinfo.dli_fbase) return true;
  }

  return false;
}

bool os::dll_address_to_function_name(address addr, char *buf,
                                      int buflen, int *offset) {
  // buf is not optional, but offset is optional
  assert(buf != NULL, "sanity check");

  Dl_info dlinfo;

  if (dladdr((void*)addr, &dlinfo) != 0) {
    // see if we have a matching symbol
    if (dlinfo.dli_saddr != NULL && dlinfo.dli_sname != NULL) {
      if (!Decoder::demangle(dlinfo.dli_sname, buf, buflen)) {
        jio_snprintf(buf, buflen, "%s", dlinfo.dli_sname);
      }
      if (offset != NULL) *offset = addr - (address)dlinfo.dli_saddr;
      return true;
    }
    // no matching symbol so try for just file info
    if (dlinfo.dli_fname != NULL && dlinfo.dli_fbase != NULL) {
      if (Decoder::decode((address)(addr - (address)dlinfo.dli_fbase),
                          buf, buflen, offset, dlinfo.dli_fname)) {
        return true;
      }
    }
  }

  buf[0] = '\0';
  if (offset != NULL) *offset = -1;
  return false;
}

struct _address_to_library_name {
  address addr;          // input : memory address
  size_t  buflen;        //         size of fname
  char*   fname;         // output: library name
  address base;          //         library base addr
};

static int address_to_library_name_callback(struct dl_phdr_info *info,
                                            size_t size, void *data) {
  int i;
  bool found = false;
  address libbase = NULL;
  struct _address_to_library_name * d = (struct _address_to_library_name *)data;

  // iterate through all loadable segments
  for (i = 0; i < info->dlpi_phnum; i++) {
    address segbase = (address)(info->dlpi_addr + info->dlpi_phdr[i].p_vaddr);
    if (info->dlpi_phdr[i].p_type == PT_LOAD) {
      // base address of a library is the lowest address of its loaded
      // segments.
      if (libbase == NULL || libbase > segbase) {
        libbase = segbase;
      }
      // see if 'addr' is within current segment
      if (segbase <= d->addr &&
          d->addr < segbase + info->dlpi_phdr[i].p_memsz) {
        found = true;
      }
    }
  }

  // dlpi_name is NULL or empty if the ELF file is executable, return 0
  // so dll_address_to_library_name() can fall through to use dladdr() which
  // can figure out executable name from argv[0].
  if (found && info->dlpi_name && info->dlpi_name[0]) {
    d->base = libbase;
    if (d->fname) {
      jio_snprintf(d->fname, d->buflen, "%s", info->dlpi_name);
    }
    return 1;
  }
  return 0;
}

bool os::dll_address_to_library_name(address addr, char* buf,
                                     int buflen, int* offset) {
  // buf is not optional, but offset is optional
  assert(buf != NULL, "sanity check");

  Dl_info dlinfo;
  struct _address_to_library_name data;

  // There is a bug in old glibc dladdr() implementation that it could resolve
  // to wrong library name if the .so file has a base address != NULL. Here
  // we iterate through the program headers of all loaded libraries to find
  // out which library 'addr' really belongs to. This workaround can be
  // removed once the minimum requirement for glibc is moved to 2.3.x.
  data.addr = addr;
  data.fname = buf;
  data.buflen = buflen;
  data.base = NULL;
  int rslt = dl_iterate_phdr(address_to_library_name_callback, (void *)&data);

  if (rslt) {
     // buf already contains library name
     if (offset) *offset = addr - data.base;
     return true;
  }
  if (dladdr((void*)addr, &dlinfo) != 0) {
    if (dlinfo.dli_fname != NULL) {
      jio_snprintf(buf, buflen, "%s", dlinfo.dli_fname);
    }
    if (dlinfo.dli_fbase != NULL && offset != NULL) {
      *offset = addr - (address)dlinfo.dli_fbase;
    }
    return true;
  }

  buf[0] = '\0';
  if (offset) *offset = -1;
  return false;
}

  // Loads .dll/.so and
  // in case of error it checks if .dll/.so was built for the
  // same architecture as Hotspot is running on


// Remember the stack's state. The Linux dynamic linker will change
// the stack to 'executable' at most once, so we must safepoint only once.
bool os::Linux::_stack_is_executable = false;

// VM operation that loads a library.  This is necessary if stack protection
// of the Java stacks can be lost during loading the library.  If we
// do not stop the Java threads, they can stack overflow before the stacks
// are protected again.
class VM_LinuxDllLoad: public VM_Operation {
 private:
  const char *_filename;
  char *_ebuf;
  int _ebuflen;
  void *_lib;
 public:
  VM_LinuxDllLoad(const char *fn, char *ebuf, int ebuflen) :
    _filename(fn), _ebuf(ebuf), _ebuflen(ebuflen), _lib(NULL) {}
  VMOp_Type type() const { return VMOp_LinuxDllLoad; }
  void doit() {
    _lib = os::Linux::dll_load_in_vmthread(_filename, _ebuf, _ebuflen);
    os::Linux::_stack_is_executable = true;
  }
  void* loaded_library() { return _lib; }
};

void * os::dll_load(const char *filename, char *ebuf, int ebuflen)
{
  void * result = NULL;
  bool load_attempted = false;

  // Check whether the library to load might change execution rights
  // of the stack. If they are changed, the protection of the stack
  // guard pages will be lost. We need a safepoint to fix this.
  //
  // See Linux man page execstack(8) for more info.
  if (os::uses_stack_guard_pages() && !os::Linux::_stack_is_executable) {
    ElfFile ef(filename);
    if (!ef.specifies_noexecstack()) {
      if (!is_init_completed()) {
        os::Linux::_stack_is_executable = true;
        // This is OK - No Java threads have been created yet, and hence no
        // stack guard pages to fix.
        //
        // This should happen only when you are building JDK7 using a very
        // old version of JDK6 (e.g., with JPRT) and running test_gamma.
        //
        // Dynamic loader will make all stacks executable after
        // this function returns, and will not do that again.
        assert(Threads::first() == NULL, "no Java threads should exist yet.");
      } else {
        warning("You have loaded library %s which might have disabled stack guard. "
                "The VM will try to fix the stack guard now.\n"
                "It's highly recommended that you fix the library with "
                "'execstack -c <libfile>', or link it with '-z noexecstack'.",
                filename);

        assert(Thread::current()->is_Java_thread(), "must be Java thread");
        JavaThread *jt = JavaThread::current();
        if (jt->thread_state() != _thread_in_native) {
          // This happens when a compiler thread tries to load a hsdis-<arch>.so file
          // that requires ExecStack. Cannot enter safe point. Let's give up.
          warning("Unable to fix stack guard. Giving up.");
        } else {
          if (!LoadExecStackDllInVMThread) {
            // This is for the case where the DLL has an static
            // constructor function that executes JNI code. We cannot
            // load such DLLs in the VMThread.
            result = os::Linux::dlopen_helper(filename, ebuf, ebuflen);
          }

          ThreadInVMfromNative tiv(jt);
          debug_only(VMNativeEntryWrapper vew;)

          VM_LinuxDllLoad op(filename, ebuf, ebuflen);
          VMThread::execute(&op);
          if (LoadExecStackDllInVMThread) {
            result = op.loaded_library();
          }
          load_attempted = true;
        }
      }
    }
  }

  if (!load_attempted) {
    result = os::Linux::dlopen_helper(filename, ebuf, ebuflen);
  }

  if (result != NULL) {
    // Successful loading
    return result;
  }

  Elf32_Ehdr elf_head;
  int diag_msg_max_length=ebuflen-strlen(ebuf);
  char* diag_msg_buf=ebuf+strlen(ebuf);

  if (diag_msg_max_length==0) {
    // No more space in ebuf for additional diagnostics message
    return NULL;
  }


  int file_descriptor= ::open(filename, O_RDONLY | O_NONBLOCK);

  if (file_descriptor < 0) {
    // Can't open library, report dlerror() message
    return NULL;
  }

  bool failed_to_read_elf_head=
    (sizeof(elf_head)!=
        (::read(file_descriptor, &elf_head,sizeof(elf_head)))) ;

  ::close(file_descriptor);
  if (failed_to_read_elf_head) {
    // file i/o error - report dlerror() msg
    return NULL;
  }

  typedef struct {
    Elf32_Half  code;         // Actual value as defined in elf.h
    Elf32_Half  compat_class; // Compatibility of archs at VM's sense
    char        elf_class;    // 32 or 64 bit
    char        endianess;    // MSB or LSB
    char*       name;         // String representation
  } arch_t;

  #ifndef EM_486
  #define EM_486          6               /* Intel 80486 */
  #endif

  static const arch_t arch_array[]={
    {EM_386,         EM_386,     ELFCLASS32, ELFDATA2LSB, (char*)"IA 32"},
    {EM_486,         EM_386,     ELFCLASS32, ELFDATA2LSB, (char*)"IA 32"},
    {EM_IA_64,       EM_IA_64,   ELFCLASS64, ELFDATA2LSB, (char*)"IA 64"},
    {EM_X86_64,      EM_X86_64,  ELFCLASS64, ELFDATA2LSB, (char*)"AMD 64"},
    {EM_SPARC,       EM_SPARC,   ELFCLASS32, ELFDATA2MSB, (char*)"Sparc 32"},
    {EM_SPARC32PLUS, EM_SPARC,   ELFCLASS32, ELFDATA2MSB, (char*)"Sparc 32"},
    {EM_SPARCV9,     EM_SPARCV9, ELFCLASS64, ELFDATA2MSB, (char*)"Sparc v9 64"},
    {EM_PPC,         EM_PPC,     ELFCLASS32, ELFDATA2MSB, (char*)"Power PC 32"},
#if defined(VM_LITTLE_ENDIAN)
    {EM_PPC64,       EM_PPC64,   ELFCLASS64, ELFDATA2LSB, (char*)"Power PC 64"},
#else
    {EM_PPC64,       EM_PPC64,   ELFCLASS64, ELFDATA2MSB, (char*)"Power PC 64"},
#endif
    {EM_ARM,         EM_ARM,     ELFCLASS32,   ELFDATA2LSB, (char*)"ARM"},
    {EM_S390,        EM_S390,    ELFCLASSNONE, ELFDATA2MSB, (char*)"IBM System/390"},
    {EM_ALPHA,       EM_ALPHA,   ELFCLASS64, ELFDATA2LSB, (char*)"Alpha"},
    {EM_MIPS_RS3_LE, EM_MIPS_RS3_LE, ELFCLASS32, ELFDATA2LSB, (char*)"MIPSel"},
    {EM_MIPS,        EM_MIPS,    ELFCLASS32, ELFDATA2MSB, (char*)"MIPS"},
    {EM_PARISC,      EM_PARISC,  ELFCLASS32, ELFDATA2MSB, (char*)"PARISC"},
    {EM_68K,         EM_68K,     ELFCLASS32, ELFDATA2MSB, (char*)"M68k"}
  };

  #if  (defined IA32)
    static  Elf32_Half running_arch_code=EM_386;
  #elif   (defined AMD64)
    static  Elf32_Half running_arch_code=EM_X86_64;
  #elif  (defined IA64)
    static  Elf32_Half running_arch_code=EM_IA_64;
  #elif  (defined __sparc) && (defined _LP64)
    static  Elf32_Half running_arch_code=EM_SPARCV9;
  #elif  (defined __sparc) && (!defined _LP64)
    static  Elf32_Half running_arch_code=EM_SPARC;
  #elif  (defined __powerpc64__)
    static  Elf32_Half running_arch_code=EM_PPC64;
  #elif  (defined __powerpc__)
    static  Elf32_Half running_arch_code=EM_PPC;
  #elif  (defined ARM)
    static  Elf32_Half running_arch_code=EM_ARM;
  #elif  (defined S390)
    static  Elf32_Half running_arch_code=EM_S390;
  #elif  (defined ALPHA)
    static  Elf32_Half running_arch_code=EM_ALPHA;
  #elif  (defined MIPSEL)
    static  Elf32_Half running_arch_code=EM_MIPS_RS3_LE;
  #elif  (defined PARISC)
    static  Elf32_Half running_arch_code=EM_PARISC;
  #elif  (defined MIPS)
    static  Elf32_Half running_arch_code=EM_MIPS;
  #elif  (defined M68K)
    static  Elf32_Half running_arch_code=EM_68K;
  #else
    #error Method os::dll_load requires that one of following is defined:\
         IA32, AMD64, IA64, __sparc, __powerpc__, ARM, S390, ALPHA, MIPS, MIPSEL, PARISC, M68K
  #endif

  // Identify compatability class for VM's architecture and library's architecture
  // Obtain string descriptions for architectures

  arch_t lib_arch={elf_head.e_machine,0,elf_head.e_ident[EI_CLASS], elf_head.e_ident[EI_DATA], NULL};
  int running_arch_index=-1;

  for (unsigned int i=0 ; i < ARRAY_SIZE(arch_array) ; i++ ) {
    if (running_arch_code == arch_array[i].code) {
      running_arch_index    = i;
    }
    if (lib_arch.code == arch_array[i].code) {
      lib_arch.compat_class = arch_array[i].compat_class;
      lib_arch.name         = arch_array[i].name;
    }
  }

  assert(running_arch_index != -1,
    "Didn't find running architecture code (running_arch_code) in arch_array");
  if (running_arch_index == -1) {
    // Even though running architecture detection failed
    // we may still continue with reporting dlerror() message
    return NULL;
  }

  if (lib_arch.endianess != arch_array[running_arch_index].endianess) {
    ::snprintf(diag_msg_buf, diag_msg_max_length-1," (Possible cause: endianness mismatch)");
    return NULL;
  }

#ifndef S390
  if (lib_arch.elf_class != arch_array[running_arch_index].elf_class) {
    ::snprintf(diag_msg_buf, diag_msg_max_length-1," (Possible cause: architecture word width mismatch)");
    return NULL;
  }
#endif // !S390

  if (lib_arch.compat_class != arch_array[running_arch_index].compat_class) {
    if ( lib_arch.name!=NULL ) {
      ::snprintf(diag_msg_buf, diag_msg_max_length-1,
        " (Possible cause: can't load %s-bit .so on a %s-bit platform)",
        lib_arch.name, arch_array[running_arch_index].name);
    } else {
      ::snprintf(diag_msg_buf, diag_msg_max_length-1,
      " (Possible cause: can't load this .so (machine code=0x%x) on a %s-bit platform)",
        lib_arch.code,
        arch_array[running_arch_index].name);
    }
  }

  return NULL;
}

void * os::Linux::dlopen_helper(const char *filename, char *ebuf, int ebuflen) {
  void * result = ::dlopen(filename, RTLD_LAZY);
  if (result == NULL) {
    ::strncpy(ebuf, ::dlerror(), ebuflen - 1);
    ebuf[ebuflen-1] = '\0';
  }
  return result;
}

void * os::Linux::dll_load_in_vmthread(const char *filename, char *ebuf, int ebuflen) {
  void * result = NULL;
  if (LoadExecStackDllInVMThread) {
    result = dlopen_helper(filename, ebuf, ebuflen);
  }

  // Since 7019808, libjvm.so is linked with -noexecstack. If the VM loads a
  // library that requires an executable stack, or which does not have this
  // stack attribute set, dlopen changes the stack attribute to executable. The
  // read protection of the guard pages gets lost.
  //
  // Need to check _stack_is_executable again as multiple VM_LinuxDllLoad
  // may have been queued at the same time.

  if (!_stack_is_executable) {
    JavaThread *jt = Threads::first();

    while (jt) {
      if (!jt->stack_guard_zone_unused() &&        // Stack not yet fully initialized
          jt->stack_yellow_zone_enabled()) {       // No pending stack overflow exceptions
        if (!os::guard_memory((char *) jt->stack_red_zone_base() - jt->stack_red_zone_size(),
                              jt->stack_yellow_zone_size() + jt->stack_red_zone_size())) {
          warning("Attempt to reguard stack yellow zone failed.");
        }
      }
      jt = jt->next();
    }
  }

  return result;
}

/*
 * glibc-2.0 libdl is not MT safe.  If you are building with any glibc,
 * chances are you might want to run the generated bits against glibc-2.0
 * libdl.so, so always use locking for any version of glibc.
 */
void* os::dll_lookup(void* handle, const char* name) {
  pthread_mutex_lock(&dl_mutex);
  void* res = dlsym(handle, name);
  pthread_mutex_unlock(&dl_mutex);
  return res;
}


static bool _print_ascii_file(const char* filename, outputStream* st) {
  int fd = ::open(filename, O_RDONLY);
  if (fd == -1) {
     return false;
  }

  char buf[32];
  int bytes;
  while ((bytes = ::read(fd, buf, sizeof(buf))) > 0) {
    st->print_raw(buf, bytes);
  }

  ::close(fd);

  return true;
}

void os::print_dll_info(outputStream *st) {
   st->print_cr("Dynamic libraries:");

   char fname[32];
   pid_t pid = os::Linux::gettid();

   jio_snprintf(fname, sizeof(fname), "/proc/%d/maps", pid);

   if (!_print_ascii_file(fname, st)) {
     st->print("Can not get library information for pid = %d\n", pid);
   }
}

void os::print_os_info_brief(outputStream* st) {
  os::Linux::print_distro_info(st);

  os::Posix::print_uname_info(st);

  os::Linux::print_libversion_info(st);

}

void os::print_os_info(outputStream* st) {
  st->print("OS:");

  os::Linux::print_distro_info(st);

  os::Posix::print_uname_info(st);

  // Print warning if unsafe chroot environment detected
  if (unsafe_chroot_detected) {
    st->print("WARNING!! ");
    st->print_cr(unstable_chroot_error);
  }

  os::Linux::print_libversion_info(st);

  os::Posix::print_rlimit_info(st);

  os::Posix::print_load_average(st);

  os::Linux::print_full_memory_info(st);
}

// Try to identify popular distros.
// Most Linux distributions have /etc/XXX-release file, which contains
// the OS version string. Some have more than one /etc/XXX-release file
// (e.g. Mandrake has both /etc/mandrake-release and /etc/redhat-release.),
// so the order is important.
void os::Linux::print_distro_info(outputStream* st) {
  if (!_print_ascii_file("/etc/mandrake-release", st) &&
      !_print_ascii_file("/etc/sun-release", st) &&
      !_print_ascii_file("/etc/redhat-release", st) &&
      !_print_ascii_file("/etc/SuSE-release", st) &&
      !_print_ascii_file("/etc/turbolinux-release", st) &&
      !_print_ascii_file("/etc/gentoo-release", st) &&
      !_print_ascii_file("/etc/debian_version", st) &&
      !_print_ascii_file("/etc/ltib-release", st) &&
      !_print_ascii_file("/etc/angstrom-version", st)) {
      st->print("Linux");
  }
  st->cr();
}

void os::Linux::print_libversion_info(outputStream* st) {
  // libc, pthread
  st->print("libc:");
  st->print(os::Linux::glibc_version()); st->print(" ");
  st->print(os::Linux::libpthread_version()); st->print(" ");
  if (os::Linux::is_LinuxThreads()) {
     st->print("(%s stack)", os::Linux::is_floating_stack() ? "floating" : "fixed");
  }
  st->cr();
}

void os::Linux::print_full_memory_info(outputStream* st) {
   st->print("\n/proc/meminfo:\n");
   _print_ascii_file("/proc/meminfo", st);
   st->cr();
}

void os::print_memory_info(outputStream* st) {

  st->print("Memory:");
  st->print(" %dk page", os::vm_page_size()>>10);

  // values in struct sysinfo are "unsigned long"
  struct sysinfo si;
  sysinfo(&si);

  st->print(", physical " UINT64_FORMAT "k",
            os::physical_memory() >> 10);
  st->print("(" UINT64_FORMAT "k free)",
            os::available_memory() >> 10);
  st->print(", swap " UINT64_FORMAT "k",
            ((jlong)si.totalswap * si.mem_unit) >> 10);
  st->print("(" UINT64_FORMAT "k free)",
            ((jlong)si.freeswap * si.mem_unit) >> 10);
  st->cr();
}

void os::pd_print_cpu_info(outputStream* st) {
  st->print("\n/proc/cpuinfo:\n");
  if (!_print_ascii_file("/proc/cpuinfo", st)) {
    st->print("  <Not Available>");
  }
  st->cr();
}

// Taken from /usr/include/bits/siginfo.h  Supposed to be architecture specific
// but they're the same for all the linux arch that we support
// and they're the same for solaris but there's no common place to put this.
const char *ill_names[] = { "ILL0", "ILL_ILLOPC", "ILL_ILLOPN", "ILL_ILLADR",
                          "ILL_ILLTRP", "ILL_PRVOPC", "ILL_PRVREG",
                          "ILL_COPROC", "ILL_BADSTK" };

const char *fpe_names[] = { "FPE0", "FPE_INTDIV", "FPE_INTOVF", "FPE_FLTDIV",
                          "FPE_FLTOVF", "FPE_FLTUND", "FPE_FLTRES",
                          "FPE_FLTINV", "FPE_FLTSUB", "FPE_FLTDEN" };

const char *segv_names[] = { "SEGV0", "SEGV_MAPERR", "SEGV_ACCERR" };

const char *bus_names[] = { "BUS0", "BUS_ADRALN", "BUS_ADRERR", "BUS_OBJERR" };

void os::print_siginfo(outputStream* st, void* siginfo) {
  st->print("siginfo:");

  const int buflen = 100;
  char buf[buflen];
  siginfo_t *si = (siginfo_t*)siginfo;
  st->print("si_signo=%s: ", os::exception_name(si->si_signo, buf, buflen));
  if (si->si_errno != 0 && strerror_r(si->si_errno, buf, buflen) == 0) {
    st->print("si_errno=%s", buf);
  } else {
    st->print("si_errno=%d", si->si_errno);
  }
  const int c = si->si_code;
  assert(c > 0, "unexpected si_code");
  switch (si->si_signo) {
  case SIGILL:
    st->print(", si_code=%d (%s)", c, c > 8 ? "" : ill_names[c]);
    st->print(", si_addr=" PTR_FORMAT, si->si_addr);
    break;
  case SIGFPE:
    st->print(", si_code=%d (%s)", c, c > 9 ? "" : fpe_names[c]);
    st->print(", si_addr=" PTR_FORMAT, si->si_addr);
    break;
  case SIGSEGV:
    st->print(", si_code=%d (%s)", c, c > 2 ? "" : segv_names[c]);
    st->print(", si_addr=" PTR_FORMAT, si->si_addr);
    break;
  case SIGBUS:
    st->print(", si_code=%d (%s)", c, c > 3 ? "" : bus_names[c]);
    st->print(", si_addr=" PTR_FORMAT, si->si_addr);
    break;
  default:
    st->print(", si_code=%d", si->si_code);
    // no si_addr
  }

  if ((si->si_signo == SIGBUS || si->si_signo == SIGSEGV) &&
      UseSharedSpaces) {
    FileMapInfo* mapinfo = FileMapInfo::current_info();
    if (mapinfo->is_in_shared_space(si->si_addr)) {
      st->print("\n\nError accessing class data sharing archive."   \
                " Mapped file inaccessible during execution, "      \
                " possible disk/network problem.");
    }
  }
  st->cr();
}


static void print_signal_handler(outputStream* st, int sig,
                                 char* buf, size_t buflen);

void os::print_signal_handlers(outputStream* st, char* buf, size_t buflen) {
  st->print_cr("Signal Handlers:");
  print_signal_handler(st, SIGSEGV, buf, buflen);
  print_signal_handler(st, SIGBUS , buf, buflen);
  print_signal_handler(st, SIGFPE , buf, buflen);
  print_signal_handler(st, SIGPIPE, buf, buflen);
  print_signal_handler(st, SIGXFSZ, buf, buflen);
  print_signal_handler(st, SIGILL , buf, buflen);
  print_signal_handler(st, INTERRUPT_SIGNAL, buf, buflen);
  print_signal_handler(st, SR_signum, buf, buflen);
  print_signal_handler(st, SHUTDOWN1_SIGNAL, buf, buflen);
  print_signal_handler(st, SHUTDOWN2_SIGNAL , buf, buflen);
  print_signal_handler(st, SHUTDOWN3_SIGNAL , buf, buflen);
  print_signal_handler(st, BREAK_SIGNAL, buf, buflen);
  print_signal_handler(st, SIGTRAP, buf, buflen);
}

static char saved_jvm_path[MAXPATHLEN] = {0};

// Find the full path to the current module, libjvm.so or libjvm_g.so
void os::jvm_path(char *buf, jint buflen) {
  // Error checking.
  if (buflen < MAXPATHLEN) {
    assert(false, "must use a large-enough buffer");
    buf[0] = '\0';
    return;
  }
  // Lazy resolve the path to current module.
  if (saved_jvm_path[0] != 0) {
    strcpy(buf, saved_jvm_path);
    return;
  }

  char dli_fname[MAXPATHLEN];
  bool ret = dll_address_to_library_name(
                CAST_FROM_FN_PTR(address, os::jvm_path),
                dli_fname, sizeof(dli_fname), NULL);
  assert(ret, "cannot locate libjvm");
  char *rp = NULL;
  if (ret && dli_fname[0] != '\0') {
    rp = realpath(dli_fname, buf);
  }
  if (rp == NULL)
    return;

  if (Arguments::created_by_gamma_launcher()) {
    // Support for the gamma launcher.  Typical value for buf is
    // "<JAVA_HOME>/jre/lib/<arch>/<vmtype>/libjvm.so".  If "/jre/lib/" appears at
    // the right place in the string, then assume we are installed in a JDK and
    // we're done.  Otherwise, check for a JAVA_HOME environment variable and fix
    // up the path so it looks like libjvm.so is installed there (append a
    // fake suffix hotspot/libjvm.so).
    const char *p = buf + strlen(buf) - 1;
    for (int count = 0; p > buf && count < 5; ++count) {
      for (--p; p > buf && *p != '/'; --p)
        /* empty */ ;
    }

    if (strncmp(p, "/jre/lib/", 9) != 0) {
      // Look for JAVA_HOME in the environment.
      char* java_home_var = ::getenv("JAVA_HOME");
      if (java_home_var != NULL && java_home_var[0] != 0) {
        char* jrelib_p;
        int len;

        // Check the current module name "libjvm.so" or "libjvm_g.so".
        p = strrchr(buf, '/');
        assert(strstr(p, "/libjvm") == p, "invalid library name");
        p = strstr(p, "_g") ? "_g" : "";

        rp = realpath(java_home_var, buf);
        if (rp == NULL)
          return;

        // determine if this is a legacy image or modules image
        // modules image doesn't have "jre" subdirectory
        len = strlen(buf);
        assert(len < buflen, "Ran out of buffer room");
        jrelib_p = buf + len;
        snprintf(jrelib_p, buflen-len, "/jre/lib/%s", cpu_arch);
        if (0 != access(buf, F_OK)) {
          snprintf(jrelib_p, buflen-len, "/lib/%s", cpu_arch);
        }

        if (0 == access(buf, F_OK)) {
          // Use current module name "libjvm[_g].so" instead of
          // "libjvm"debug_only("_g")".so" since for fastdebug version
          // we should have "libjvm.so" but debug_only("_g") adds "_g"!
          len = strlen(buf);
          snprintf(buf + len, buflen-len, "/hotspot/libjvm%s.so", p);
        } else {
          // Go back to path of .so
          rp = realpath(dli_fname, buf);
          if (rp == NULL)
            return;
        }
      }
    }
  }

  strncpy(saved_jvm_path, buf, MAXPATHLEN);
}

void os::print_jni_name_prefix_on(outputStream* st, int args_size) {
  // no prefix required, not even "_"
}

void os::print_jni_name_suffix_on(outputStream* st, int args_size) {
  // no suffix required
}

////////////////////////////////////////////////////////////////////////////////
// sun.misc.Signal support

static volatile jint sigint_count = 0;

static void
UserHandler(int sig, void *siginfo, void *context) {
  // 4511530 - sem_post is serialized and handled by the manager thread. When
  // the program is interrupted by Ctrl-C, SIGINT is sent to every thread. We
  // don't want to flood the manager thread with sem_post requests.
  if (sig == SIGINT && Atomic::add(1, &sigint_count) > 1)
      return;

  // Ctrl-C is pressed during error reporting, likely because the error
  // handler fails to abort. Let VM die immediately.
  if (sig == SIGINT && is_error_reported()) {
     os::die();
  }

  os::signal_notify(sig);
}

void* os::user_handler() {
  return CAST_FROM_FN_PTR(void*, UserHandler);
}

class Semaphore : public StackObj {
  public:
    Semaphore();
    ~Semaphore();
    void signal();
    void wait();
    bool trywait();
    bool timedwait(unsigned int sec, int nsec);
  private:
    sem_t _semaphore;
};

Semaphore::Semaphore() {
  sem_init(&_semaphore, 0, 0);
}

Semaphore::~Semaphore() {
  sem_destroy(&_semaphore);
}

void Semaphore::signal() {
  sem_post(&_semaphore);
}

void Semaphore::wait() {
  sem_wait(&_semaphore);
}

bool Semaphore::trywait() {
  return sem_trywait(&_semaphore) == 0;
}

bool Semaphore::timedwait(unsigned int sec, int nsec) {

  struct timespec ts;
  // Semaphore's are always associated with CLOCK_REALTIME
  os::Linux::clock_gettime(CLOCK_REALTIME, &ts);
  // see unpackTime for discussion on overflow checking
  if (sec >= MAX_SECS) {
    ts.tv_sec += MAX_SECS;
    ts.tv_nsec = 0;
  } else {
    ts.tv_sec += sec;
    ts.tv_nsec += nsec;
    if (ts.tv_nsec >= NANOSECS_PER_SEC) {
      ts.tv_nsec -= NANOSECS_PER_SEC;
      ++ts.tv_sec; // note: this must be <= max_secs
    }
  }

  while (1) {
    int result = sem_timedwait(&_semaphore, &ts);
    if (result == 0) {
      return true;
    } else if (errno == EINTR) {
      continue;
    } else if (errno == ETIMEDOUT) {
      return false;
    } else {
      return false;
    }
  }
}

extern "C" {
  typedef void (*sa_handler_t)(int);
  typedef void (*sa_sigaction_t)(int, siginfo_t *, void *);
}

void* os::signal(int signal_number, void* handler) {
  struct sigaction sigAct, oldSigAct;

  sigfillset(&(sigAct.sa_mask));
  sigAct.sa_flags   = SA_RESTART|SA_SIGINFO;
  sigAct.sa_handler = CAST_TO_FN_PTR(sa_handler_t, handler);

  if (sigaction(signal_number, &sigAct, &oldSigAct)) {
    // -1 means registration failed
    return (void *)-1;
  }

  return CAST_FROM_FN_PTR(void*, oldSigAct.sa_handler);
}

void os::signal_raise(int signal_number) {
  ::raise(signal_number);
}

/*
 * The following code is moved from os.cpp for making this
 * code platform specific, which it is by its very nature.
 */

// Will be modified when max signal is changed to be dynamic
int os::sigexitnum_pd() {
  return NSIG;
}

// a counter for each possible signal value
static volatile jint pending_signals[NSIG+1] = { 0 };

// Linux(POSIX) specific hand shaking semaphore.
static sem_t sig_sem;
static Semaphore sr_semaphore;

void os::signal_init_pd() {
  // Initialize signal structures
  ::memset((void*)pending_signals, 0, sizeof(pending_signals));

  // Initialize signal semaphore
  ::sem_init(&sig_sem, 0, 0);
}

void os::signal_notify(int sig) {
  Atomic::inc(&pending_signals[sig]);
  ::sem_post(&sig_sem);
}

static int check_pending_signals(bool wait) {
  Atomic::store(0, &sigint_count);
  for (;;) {
    for (int i = 0; i < NSIG + 1; i++) {
      jint n = pending_signals[i];
      if (n > 0 && n == Atomic::cmpxchg(n - 1, &pending_signals[i], n)) {
        return i;
      }
    }
    if (!wait) {
      return -1;
    }
    JavaThread *thread = JavaThread::current();
    ThreadBlockInVM tbivm(thread);

    bool threadIsSuspended;
    do {
      thread->set_suspend_equivalent();
      // cleared by handle_special_suspend_equivalent_condition() or java_suspend_self()
      ::sem_wait(&sig_sem);

      // were we externally suspended while we were waiting?
      threadIsSuspended = thread->handle_special_suspend_equivalent_condition();
      if (threadIsSuspended) {
        //
        // The semaphore has been incremented, but while we were waiting
        // another thread suspended us. We don't want to continue running
        // while suspended because that would surprise the thread that
        // suspended us.
        //
        ::sem_post(&sig_sem);

        thread->java_suspend_self();
      }
    } while (threadIsSuspended);
  }
}

int os::signal_lookup() {
  return check_pending_signals(false);
}

int os::signal_wait() {
  return check_pending_signals(true);
}

////////////////////////////////////////////////////////////////////////////////
// Virtual Memory

int os::vm_page_size() {
  // Seems redundant as all get out
  assert(os::Linux::page_size() != -1, "must call os::init");
  return os::Linux::page_size();
}

// Solaris allocates memory by pages.
int os::vm_allocation_granularity() {
  assert(os::Linux::page_size() != -1, "must call os::init");
  return os::Linux::page_size();
}

// Rationale behind this function:
//  current (Mon Apr 25 20:12:18 MSD 2005) oprofile drops samples without executable
//  mapping for address (see lookup_dcookie() in the kernel module), thus we cannot get
//  samples for JITted code. Here we create private executable mapping over the code cache
//  and then we can use standard (well, almost, as mapping can change) way to provide
//  info for the reporting script by storing timestamp and location of symbol
void linux_wrap_code(char* base, size_t size) {
  static volatile jint cnt = 0;

  if (!UseOprofile) {
    return;
  }

  char buf[PATH_MAX+1];
  int num = Atomic::add(1, &cnt);

  snprintf(buf, sizeof(buf), "%s/hs-vm-%d-%d",
           os::get_temp_directory(), os::current_process_id(), num);
  unlink(buf);

  int fd = ::open(buf, O_CREAT | O_RDWR, S_IRWXU);

  if (fd != -1) {
    off_t rv = ::lseek(fd, size-2, SEEK_SET);
    if (rv != (off_t)-1) {
      if (::write(fd, "", 1) == 1) {
        mmap(base, size,
             PROT_READ|PROT_WRITE|PROT_EXEC,
             MAP_PRIVATE|MAP_FIXED|MAP_NORESERVE, fd, 0);
      }
    }
    ::close(fd);
    unlink(buf);
  }
}

static bool recoverable_mmap_error(int err) {
  // See if the error is one we can let the caller handle. This
  // list of errno values comes from JBS-6843484. I can't find a
  // Linux man page that documents this specific set of errno
  // values so while this list currently matches Solaris, it may
  // change as we gain experience with this failure mode.
  switch (err) {
  case EBADF:
  case EINVAL:
  case ENOTSUP:
    // let the caller deal with these errors
    return true;

  default:
    // Any remaining errors on this OS can cause our reserved mapping
    // to be lost. That can cause confusion where different data
    // structures think they have the same memory mapped. The worst
    // scenario is if both the VM and a library think they have the
    // same memory mapped.
    return false;
  }
}

static void warn_fail_commit_memory(char* addr, size_t size, bool exec,
                                    int err) {
  warning("INFO: os::commit_memory(" PTR_FORMAT ", " SIZE_FORMAT
          ", %d) failed; error='%s' (errno=%d)", addr, size, exec,
          strerror(err), err);
}

static void warn_fail_commit_memory(char* addr, size_t size,
                                    size_t alignment_hint, bool exec,
                                    int err) {
  warning("INFO: os::commit_memory(" PTR_FORMAT ", " SIZE_FORMAT
          ", " SIZE_FORMAT ", %d) failed; error='%s' (errno=%d)", addr, size,
          alignment_hint, exec, strerror(err), err);
}

// NOTE: Linux kernel does not really reserve the pages for us.
//       All it does is to check if there are enough free pages
//       left at the time of mmap(). This could be a potential
//       problem.
int os::Linux::commit_memory_impl(char* addr, size_t size, bool exec) {
  int prot = exec ? PROT_READ|PROT_WRITE|PROT_EXEC : PROT_READ|PROT_WRITE;
  uintptr_t res = (uintptr_t) ::mmap(addr, size, prot,
                                   MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0);
  if (res != (uintptr_t) MAP_FAILED) {
    if (UseNUMAInterleaving) {
      numa_make_global(addr, size);
    }
    return 0;
  }

  int err = errno;  // save errno from mmap() call above

  if (!recoverable_mmap_error(err)) {
    warn_fail_commit_memory(addr, size, exec, err);
    vm_exit_out_of_memory(size, "committing reserved memory.");
  }

  return err;
}

bool os::pd_commit_memory(char* addr, size_t size, bool exec) {
  return os::Linux::commit_memory_impl(addr, size, exec) == 0;
}

void os::pd_commit_memory_or_exit(char* addr, size_t size, bool exec,
                                  const char* mesg) {
  assert(mesg != NULL, "mesg must be specified");
  int err = os::Linux::commit_memory_impl(addr, size, exec);
  if (err != 0) {
    // the caller wants all commit errors to exit with the specified mesg:
    warn_fail_commit_memory(addr, size, exec, err);
    vm_exit_out_of_memory(size, mesg);
  }
}

// Define MAP_HUGETLB here so we can build HotSpot on old systems.
#ifndef MAP_HUGETLB
#define MAP_HUGETLB 0x40000
#endif

// Define MADV_HUGEPAGE here so we can build HotSpot on old systems.
#ifndef MADV_HUGEPAGE
#define MADV_HUGEPAGE 14
#endif

int os::Linux::commit_memory_impl(char* addr, size_t size,
                                  size_t alignment_hint, bool exec) {
  int err = os::Linux::commit_memory_impl(addr, size, exec);
  if (err == 0) {
    realign_memory(addr, size, alignment_hint);
  }
  return err;
}

bool os::pd_commit_memory(char* addr, size_t size, size_t alignment_hint,
                          bool exec) {
  return os::Linux::commit_memory_impl(addr, size, alignment_hint, exec) == 0;
}

void os::pd_commit_memory_or_exit(char* addr, size_t size,
                                  size_t alignment_hint, bool exec,
                                  const char* mesg) {
  assert(mesg != NULL, "mesg must be specified");
  int err = os::Linux::commit_memory_impl(addr, size, alignment_hint, exec);
  if (err != 0) {
    // the caller wants all commit errors to exit with the specified mesg:
    warn_fail_commit_memory(addr, size, alignment_hint, exec, err);
    vm_exit_out_of_memory(size, mesg);
  }
}

void os::pd_realign_memory(char *addr, size_t bytes, size_t alignment_hint) {
  if (UseTransparentHugePages && alignment_hint > (size_t)vm_page_size()) {
    // We don't check the return value: madvise(MADV_HUGEPAGE) may not
    // be supported or the memory may already be backed by huge pages.
    ::madvise(addr, bytes, MADV_HUGEPAGE);
  }
}

void os::pd_free_memory(char *addr, size_t bytes, size_t alignment_hint) {
  // This method works by doing an mmap over an existing mmaping and effectively discarding
  // the existing pages. However it won't work for SHM-based large pages that cannot be
  // uncommitted at all. We don't do anything in this case to avoid creating a segment with
  // small pages on top of the SHM segment. This method always works for small pages, so we
  // allow that in any case.
  if (alignment_hint <= (size_t)os::vm_page_size() || can_commit_large_page_memory()) {
    commit_memory(addr, bytes, alignment_hint, !ExecMem);
  }
}

void os::numa_make_global(char *addr, size_t bytes) {
  Linux::numa_interleave_memory(addr, bytes);
}

void os::numa_make_local(char *addr, size_t bytes, int lgrp_hint) {
  Linux::numa_tonode_memory(addr, bytes, lgrp_hint);
}

bool os::numa_topology_changed()   { return false; }

size_t os::numa_get_groups_num() {
  int max_node = Linux::numa_max_node();
  return max_node > 0 ? max_node + 1 : 1;
}

int os::numa_get_group_id() {
  int cpu_id = Linux::sched_getcpu();
  if (cpu_id != -1) {
    int lgrp_id = Linux::get_node_by_cpu(cpu_id);
    if (lgrp_id != -1) {
      return lgrp_id;
    }
  }
  return 0;
}

size_t os::numa_get_leaf_groups(int *ids, size_t size) {
  for (size_t i = 0; i < size; i++) {
    ids[i] = i;
  }
  return size;
}

bool os::get_page_info(char *start, page_info* info) {
  return false;
}

char *os::scan_pages(char *start, char* end, page_info* page_expected, page_info* page_found) {
  return end;
}


int os::Linux::sched_getcpu_syscall(void) {
  unsigned int cpu;
  int retval = -1;

#if defined(IA32)
# ifndef SYS_getcpu
# define SYS_getcpu 318
# endif
  retval = syscall(SYS_getcpu, &cpu, NULL, NULL);
#elif defined(AMD64)
// Unfortunately we have to bring all these macros here from vsyscall.h
// to be able to compile on old linuxes.
# define __NR_vgetcpu 2
# define VSYSCALL_START (-10UL << 20)
# define VSYSCALL_SIZE 1024
# define VSYSCALL_ADDR(vsyscall_nr) (VSYSCALL_START+VSYSCALL_SIZE*(vsyscall_nr))
  typedef long (*vgetcpu_t)(unsigned int *cpu, unsigned int *node, unsigned long *tcache);
  vgetcpu_t vgetcpu = (vgetcpu_t)VSYSCALL_ADDR(__NR_vgetcpu);
  retval = vgetcpu(&cpu, NULL, NULL);
#endif

  return (retval == -1) ? retval : cpu;
}

// Something to do with the numa-aware allocator needs these symbols
extern "C" JNIEXPORT void numa_warn(int number, char *where, ...) { }
extern "C" JNIEXPORT void numa_error(char *where) { }
extern "C" JNIEXPORT int fork1() { return fork(); }


// If we are running with libnuma version > 2, then we should
// be trying to use symbols with versions 1.1
// If we are running with earlier version, which did not have symbol versions,
// we should use the base version.
void* os::Linux::libnuma_dlsym(void* handle, const char *name) {
  void *f = dlvsym(handle, name, "libnuma_1.1");
  if (f == NULL) {
    f = dlsym(handle, name);
  }
  return f;
}

bool os::Linux::libnuma_init() {
  // sched_getcpu() should be in libc.
  set_sched_getcpu(CAST_TO_FN_PTR(sched_getcpu_func_t,
                                  dlsym(RTLD_DEFAULT, "sched_getcpu")));

  // If it's not, try a direct syscall.
  if (sched_getcpu() == -1)
    set_sched_getcpu(CAST_TO_FN_PTR(sched_getcpu_func_t, (void*)&sched_getcpu_syscall));

  if (sched_getcpu() != -1) { // Does it work?
    void *handle = dlopen("libnuma.so.1", RTLD_LAZY);
    if (handle != NULL) {
      set_numa_node_to_cpus(CAST_TO_FN_PTR(numa_node_to_cpus_func_t,
                                           libnuma_dlsym(handle, "numa_node_to_cpus")));
      set_numa_max_node(CAST_TO_FN_PTR(numa_max_node_func_t,
                                       libnuma_dlsym(handle, "numa_max_node")));
      set_numa_available(CAST_TO_FN_PTR(numa_available_func_t,
                                        libnuma_dlsym(handle, "numa_available")));
      set_numa_tonode_memory(CAST_TO_FN_PTR(numa_tonode_memory_func_t,
                                            libnuma_dlsym(handle, "numa_tonode_memory")));
      set_numa_interleave_memory(CAST_TO_FN_PTR(numa_interleave_memory_func_t,
                                            libnuma_dlsym(handle, "numa_interleave_memory")));


      if (numa_available() != -1) {
        set_numa_all_nodes((unsigned long*)libnuma_dlsym(handle, "numa_all_nodes"));
        // Create a cpu -> node mapping
        _cpu_to_node = new (ResourceObj::C_HEAP, mtInternal) GrowableArray<int>(0, true);
        rebuild_cpu_to_node_map();
        return true;
      }
    }
  }
  return false;
}

// rebuild_cpu_to_node_map() constructs a table mapping cpud id to node id.
// The table is later used in get_node_by_cpu().
void os::Linux::rebuild_cpu_to_node_map() {
  const size_t NCPUS = 32768; // Since the buffer size computation is very obscure
                              // in libnuma (possible values are starting from 16,
                              // and continuing up with every other power of 2, but less
                              // than the maximum number of CPUs supported by kernel), and
                              // is a subject to change (in libnuma version 2 the requirements
                              // are more reasonable) we'll just hardcode the number they use
                              // in the library.
  const size_t BitsPerCLong = sizeof(long) * CHAR_BIT;

  size_t cpu_num = os::active_processor_count();
  size_t cpu_map_size = NCPUS / BitsPerCLong;
  size_t cpu_map_valid_size =
    MIN2((cpu_num + BitsPerCLong - 1) / BitsPerCLong, cpu_map_size);

  cpu_to_node()->clear();
  cpu_to_node()->at_grow(cpu_num - 1);
  size_t node_num = numa_get_groups_num();

  unsigned long *cpu_map = NEW_C_HEAP_ARRAY(unsigned long, cpu_map_size, mtInternal);
  for (size_t i = 0; i < node_num; i++) {
    if (numa_node_to_cpus(i, cpu_map, cpu_map_size * sizeof(unsigned long)) != -1) {
      for (size_t j = 0; j < cpu_map_valid_size; j++) {
        if (cpu_map[j] != 0) {
          for (size_t k = 0; k < BitsPerCLong; k++) {
            if (cpu_map[j] & (1UL << k)) {
              cpu_to_node()->at_put(j * BitsPerCLong + k, i);
            }
          }
        }
      }
    }
  }
  FREE_C_HEAP_ARRAY(unsigned long, cpu_map, mtInternal);
}

int os::Linux::get_node_by_cpu(int cpu_id) {
  if (cpu_to_node() != NULL && cpu_id >= 0 && cpu_id < cpu_to_node()->length()) {
    return cpu_to_node()->at(cpu_id);
  }
  return -1;
}

GrowableArray<int>* os::Linux::_cpu_to_node;
os::Linux::sched_getcpu_func_t os::Linux::_sched_getcpu;
os::Linux::numa_node_to_cpus_func_t os::Linux::_numa_node_to_cpus;
os::Linux::numa_max_node_func_t os::Linux::_numa_max_node;
os::Linux::numa_available_func_t os::Linux::_numa_available;
os::Linux::numa_tonode_memory_func_t os::Linux::_numa_tonode_memory;
os::Linux::numa_interleave_memory_func_t os::Linux::_numa_interleave_memory;
unsigned long* os::Linux::_numa_all_nodes;

bool os::pd_uncommit_memory(char* addr, size_t size) {
  uintptr_t res = (uintptr_t) ::mmap(addr, size, PROT_NONE,
                MAP_PRIVATE|MAP_FIXED|MAP_NORESERVE|MAP_ANONYMOUS, -1, 0);
  return res  != (uintptr_t) MAP_FAILED;
}

// Linux uses a growable mapping for the stack, and if the mapping for
// the stack guard pages is not removed when we detach a thread the
// stack cannot grow beyond the pages where the stack guard was
// mapped.  If at some point later in the process the stack expands to
// that point, the Linux kernel cannot expand the stack any further
// because the guard pages are in the way, and a segfault occurs.
//
// However, it's essential not to split the stack region by unmapping
// a region (leaving a hole) that's already part of the stack mapping,
// so if the stack mapping has already grown beyond the guard pages at
// the time we create them, we have to truncate the stack mapping.
// So, we need to know the extent of the stack mapping when
// create_stack_guard_pages() is called.

// Find the bounds of the stack mapping.  Return true for success.
//
// We only need this for stacks that are growable: at the time of
// writing thread stacks don't use growable mappings (i.e. those
// creeated with MAP_GROWSDOWN), and aren't marked "[stack]", so this
// only applies to the main thread.

static
bool get_stack_bounds(uintptr_t *bottom, uintptr_t *top) {

  char buf[128];
  int fd, sz;

  if ((fd = ::open("/proc/self/maps", O_RDONLY)) < 0) {
    return false;
  }

  const char kw[] = "[stack]";
  const int kwlen = sizeof(kw)-1;

  // Address part of /proc/self/maps couldn't be more than 128 bytes
  while ((sz = os::get_line_chars(fd, buf, sizeof(buf))) > 0) {
     if (sz > kwlen && ::memcmp(buf+sz-kwlen, kw, kwlen) == 0) {
        // Extract addresses
        if (sscanf(buf, "%" SCNxPTR "-%" SCNxPTR, bottom, top) == 2) {
           uintptr_t sp = (uintptr_t) __builtin_frame_address(0);
           if (sp >= *bottom && sp <= *top) {
              ::close(fd);
              return true;
           }
        }
     }
  }

 ::close(fd);
  return false;
}


// If the (growable) stack mapping already extends beyond the point
// where we're going to put our guard pages, truncate the mapping at
// that point by munmap()ping it.  This ensures that when we later
// munmap() the guard pages we don't leave a hole in the stack
// mapping. This only affects the main/initial thread, but guard
// against future OS changes
bool os::pd_create_stack_guard_pages(char* addr, size_t size) {
  uintptr_t stack_extent, stack_base;
  bool chk_bounds = NOT_DEBUG(os::Linux::is_initial_thread()) DEBUG_ONLY(true);
  if (chk_bounds && get_stack_bounds(&stack_extent, &stack_base)) {
      assert(os::Linux::is_initial_thread(),
           "growable stack in non-initial thread");
    if (stack_extent < (uintptr_t)addr)
      ::munmap((void*)stack_extent, (uintptr_t)addr - stack_extent);
  }

  return os::commit_memory(addr, size, !ExecMem);
}

// If this is a growable mapping, remove the guard pages entirely by
// munmap()ping them.  If not, just call uncommit_memory(). This only
// affects the main/initial thread, but guard against future OS changes
bool os::remove_stack_guard_pages(char* addr, size_t size) {
  uintptr_t stack_extent, stack_base;
  bool chk_bounds = NOT_DEBUG(os::Linux::is_initial_thread()) DEBUG_ONLY(true);
  if (chk_bounds && get_stack_bounds(&stack_extent, &stack_base)) {
      assert(os::Linux::is_initial_thread(),
           "growable stack in non-initial thread");

    return ::munmap(addr, size) == 0;
  }

  return os::uncommit_memory(addr, size);
}

static address _highest_vm_reserved_address = NULL;

// If 'fixed' is true, anon_mmap() will attempt to reserve anonymous memory
// at 'requested_addr'. If there are existing memory mappings at the same
// location, however, they will be overwritten. If 'fixed' is false,
// 'requested_addr' is only treated as a hint, the return value may or
// may not start from the requested address. Unlike Linux mmap(), this
// function returns NULL to indicate failure.
static char* anon_mmap(char* requested_addr, size_t bytes, bool fixed) {
  char * addr;
  int flags;

  flags = MAP_PRIVATE | MAP_NORESERVE | MAP_ANONYMOUS;
  if (fixed) {
    assert((uintptr_t)requested_addr % os::Linux::page_size() == 0, "unaligned address");
    flags |= MAP_FIXED;
  }

  // Map uncommitted pages PROT_READ and PROT_WRITE, change access
  // to PROT_EXEC if executable when we commit the page.
  addr = (char*)::mmap(requested_addr, bytes, PROT_READ|PROT_WRITE,
                       flags, -1, 0);

  if (addr != MAP_FAILED) {
    // anon_mmap() should only get called during VM initialization,
    // don't need lock (actually we can skip locking even it can be called
    // from multiple threads, because _highest_vm_reserved_address is just a
    // hint about the upper limit of non-stack memory regions.)
    if ((address)addr + bytes > _highest_vm_reserved_address) {
      _highest_vm_reserved_address = (address)addr + bytes;
    }
  }

  return addr == MAP_FAILED ? NULL : addr;
}

// Don't update _highest_vm_reserved_address, because there might be memory
// regions above addr + size. If so, releasing a memory region only creates
// a hole in the address space, it doesn't help prevent heap-stack collision.
//
static int anon_munmap(char * addr, size_t size) {
  return ::munmap(addr, size) == 0;
}

char* os::pd_reserve_memory(size_t bytes, char* requested_addr,
                         size_t alignment_hint) {
  return anon_mmap(requested_addr, bytes, (requested_addr != NULL));
}

bool os::pd_release_memory(char* addr, size_t size) {
  return anon_munmap(addr, size);
}

static address highest_vm_reserved_address() {
  return _highest_vm_reserved_address;
}

static bool linux_mprotect(char* addr, size_t size, int prot) {
  // Linux wants the mprotect address argument to be page aligned.
  char* bottom = (char*)align_size_down((intptr_t)addr, os::Linux::page_size());

  // According to SUSv3, mprotect() should only be used with mappings
  // established by mmap(), and mmap() always maps whole pages. Unaligned
  // 'addr' likely indicates problem in the VM (e.g. trying to change
  // protection of malloc'ed or statically allocated memory). Check the
  // caller if you hit this assert.
  assert(addr == bottom, "sanity check");

  size = align_size_up(pointer_delta(addr, bottom, 1) + size, os::Linux::page_size());
  return ::mprotect(bottom, size, prot) == 0;
}

// Set protections specified
bool os::protect_memory(char* addr, size_t bytes, ProtType prot,
                        bool is_committed) {
  unsigned int p = 0;
  switch (prot) {
  case MEM_PROT_NONE: p = PROT_NONE; break;
  case MEM_PROT_READ: p = PROT_READ; break;
  case MEM_PROT_RW:   p = PROT_READ|PROT_WRITE; break;
  case MEM_PROT_RWX:  p = PROT_READ|PROT_WRITE|PROT_EXEC; break;
  default:
    ShouldNotReachHere();
  }
  // is_committed is unused.
  return linux_mprotect(addr, bytes, p);
}

bool os::guard_memory(char* addr, size_t size) {
  return linux_mprotect(addr, size, PROT_NONE);
}

bool os::unguard_memory(char* addr, size_t size) {
  return linux_mprotect(addr, size, PROT_READ|PROT_WRITE);
}

bool os::Linux::transparent_huge_pages_sanity_check(bool warn, size_t page_size) {
  bool result = false;
  void *p = mmap(NULL, page_size * 2, PROT_READ|PROT_WRITE,
                 MAP_ANONYMOUS|MAP_PRIVATE,
                 -1, 0);
  if (p != MAP_FAILED) {
    void *aligned_p = align_ptr_up(p, page_size);

    result = madvise(aligned_p, page_size, MADV_HUGEPAGE) == 0;

    munmap(p, page_size * 2);
  }

  if (warn && !result) {
    warning("TransparentHugePages is not supported by the operating system.");
  }

  return result;
}

bool os::Linux::hugetlbfs_sanity_check(bool warn, size_t page_size) {
  bool result = false;
  void *p = mmap(NULL, page_size, PROT_READ|PROT_WRITE,
                 MAP_ANONYMOUS|MAP_PRIVATE|MAP_HUGETLB,
                 -1, 0);

  if (p != MAP_FAILED) {
    // We don't know if this really is a huge page or not.
    FILE *fp = fopen("/proc/self/maps", "r");
    if (fp) {
      while (!feof(fp)) {
        char chars[257];
        long x = 0;
        if (fgets(chars, sizeof(chars), fp)) {
          if (sscanf(chars, "%lx-%*x", &x) == 1
              && x == (long)p) {
            if (strstr (chars, "hugepage")) {
              result = true;
              break;
            }
          }
        }
      }
      fclose(fp);
    }
    munmap(p, page_size);
  }

  if (warn && !result) {
    warning("HugeTLBFS is not supported by the operating system.");
  }

  return result;
}

/*
* Set the coredump_filter bits to include largepages in core dump (bit 6)
*
* From the coredump_filter documentation:
*
* - (bit 0) anonymous private memory
* - (bit 1) anonymous shared memory
* - (bit 2) file-backed private memory
* - (bit 3) file-backed shared memory
* - (bit 4) ELF header pages in file-backed private memory areas (it is
*           effective only if the bit 2 is cleared)
* - (bit 5) hugetlb private memory
* - (bit 6) hugetlb shared memory
*/
static void set_coredump_filter(void) {
  FILE *f;
  long cdm;

  if ((f = fopen("/proc/self/coredump_filter", "r+")) == NULL) {
    return;
  }

  if (fscanf(f, "%lx", &cdm) != 1) {
    fclose(f);
    return;
  }

  rewind(f);

  if ((cdm & LARGEPAGES_BIT) == 0) {
    cdm |= LARGEPAGES_BIT;
    fprintf(f, "%#lx", cdm);
  }

  fclose(f);
}

// Large page support

static size_t _large_page_size = 0;

size_t os::Linux::find_large_page_size() {
  size_t large_page_size = 0;

  // large_page_size on Linux is used to round up heap size. x86 uses either
  // 2M or 4M page, depending on whether PAE (Physical Address Extensions)
  // mode is enabled. AMD64/EM64T uses 2M page in 64bit mode. IA64 can use
  // page as large as 256M.
  //
  // Here we try to figure out page size by parsing /proc/meminfo and looking
  // for a line with the following format:
  //    Hugepagesize:     2048 kB
  //
  // If we can't determine the value (e.g. /proc is not mounted, or the text
  // format has been changed), we'll use the largest page size supported by
  // the processor.

#ifndef ZERO
  large_page_size = IA32_ONLY(4 * M) AMD64_ONLY(2 * M) IA64_ONLY(256 * M) SPARC_ONLY(4 * M)
                     ARM_ONLY(2 * M) PPC_ONLY(4 * M);
#endif // ZERO

  FILE *fp = fopen("/proc/meminfo", "r");
  if (fp) {
    while (!feof(fp)) {
      int x = 0;
      char buf[16];
      if (fscanf(fp, "Hugepagesize: %d", &x) == 1) {
        if (x && fgets(buf, sizeof(buf), fp) && strcmp(buf, " kB\n") == 0) {
          large_page_size = x * K;
          break;
        }
      } else {
        // skip to next line
        for (;;) {
          int ch = fgetc(fp);
          if (ch == EOF || ch == (int)'\n') break;
        }
      }
    }
    fclose(fp);
  }

  if (!FLAG_IS_DEFAULT(LargePageSizeInBytes) && LargePageSizeInBytes != large_page_size) {
    warning("Setting LargePageSizeInBytes has no effect on this OS. Large page size is "
        SIZE_FORMAT "%s.", byte_size_in_proper_unit(large_page_size),
        proper_unit_for_byte_size(large_page_size));
  }

  return large_page_size;
}

size_t os::Linux::setup_large_page_size() {
  _large_page_size = Linux::find_large_page_size();
  const size_t default_page_size = (size_t)Linux::page_size();
  if (_large_page_size > default_page_size) {
    _page_sizes[0] = _large_page_size;
    _page_sizes[1] = default_page_size;
    _page_sizes[2] = 0;
  }

  return _large_page_size;
}

bool os::Linux::setup_large_page_type(size_t page_size) {
  if (FLAG_IS_DEFAULT(UseHugeTLBFS) &&
      FLAG_IS_DEFAULT(UseSHM) &&
      FLAG_IS_DEFAULT(UseTransparentHugePages)) {

    // The type of large pages has not been specified by the user.

    // Try UseHugeTLBFS and then UseSHM.
    UseHugeTLBFS = UseSHM = true;

    // Don't try UseTransparentHugePages since there are known
    // performance issues with it turned on. This might change in the future.
    UseTransparentHugePages = false;
  }

  if (UseTransparentHugePages) {
    bool warn_on_failure = !FLAG_IS_DEFAULT(UseTransparentHugePages);
    if (transparent_huge_pages_sanity_check(warn_on_failure, page_size)) {
      UseHugeTLBFS = false;
      UseSHM = false;
      return true;
    }
    UseTransparentHugePages = false;
  }

  if (UseHugeTLBFS) {
    bool warn_on_failure = !FLAG_IS_DEFAULT(UseHugeTLBFS);
    if (hugetlbfs_sanity_check(warn_on_failure, page_size)) {
      UseSHM = false;
      return true;
    }
    UseHugeTLBFS = false;
  }

  return UseSHM;
}

void os::large_page_init() {
  if (!UseLargePages &&
      !UseTransparentHugePages &&
      !UseHugeTLBFS &&
      !UseSHM) {
    // Not using large pages.
    return;
  }

  if (!FLAG_IS_DEFAULT(UseLargePages) && !UseLargePages) {
    // The user explicitly turned off large pages.
    // Ignore the rest of the large pages flags.
    UseTransparentHugePages = false;
    UseHugeTLBFS = false;
    UseSHM = false;
    return;
  }

  size_t large_page_size = Linux::setup_large_page_size();
  UseLargePages          = Linux::setup_large_page_type(large_page_size);

  set_coredump_filter();
}

#ifndef SHM_HUGETLB
#define SHM_HUGETLB 04000
#endif

char* os::Linux::reserve_memory_special_shm(size_t bytes, size_t alignment, char* req_addr, bool exec) {
  // "exec" is passed in but not used.  Creating the shared image for
  // the code cache doesn't have an SHM_X executable permission to check.
  assert(UseLargePages && UseSHM, "only for SHM large pages");
  assert(is_ptr_aligned(req_addr, os::large_page_size()), "Unaligned address");

  if (!is_size_aligned(bytes, os::large_page_size()) || alignment > os::large_page_size()) {
    return NULL; // Fallback to small pages.
  }

  key_t key = IPC_PRIVATE;
  char *addr;

  bool warn_on_failure = UseLargePages &&
                        (!FLAG_IS_DEFAULT(UseLargePages) ||
                         !FLAG_IS_DEFAULT(UseSHM) ||
                         !FLAG_IS_DEFAULT(LargePageSizeInBytes)
                        );
  char msg[128];

  // Create a large shared memory region to attach to based on size.
  // Currently, size is the total size of the heap
  int shmid = shmget(key, bytes, SHM_HUGETLB|IPC_CREAT|SHM_R|SHM_W);
  if (shmid == -1) {
     // Possible reasons for shmget failure:
     // 1. shmmax is too small for Java heap.
     //    > check shmmax value: cat /proc/sys/kernel/shmmax
     //    > increase shmmax value: echo "0xffffffff" > /proc/sys/kernel/shmmax
     // 2. not enough large page memory.
     //    > check available large pages: cat /proc/meminfo
     //    > increase amount of large pages:
     //          echo new_value > /proc/sys/vm/nr_hugepages
     //      Note 1: different Linux may use different name for this property,
     //            e.g. on Redhat AS-3 it is "hugetlb_pool".
     //      Note 2: it's possible there's enough physical memory available but
     //            they are so fragmented after a long run that they can't
     //            coalesce into large pages. Try to reserve large pages when
     //            the system is still "fresh".
     if (warn_on_failure) {
       jio_snprintf(msg, sizeof(msg), "Failed to reserve shared memory (errno = %d).", errno);
       warning(msg);
     }
     return NULL;
  }

  // attach to the region
  addr = (char*)shmat(shmid, req_addr, 0);
  int err = errno;

  // Remove shmid. If shmat() is successful, the actual shared memory segment
  // will be deleted when it's detached by shmdt() or when the process
  // terminates. If shmat() is not successful this will remove the shared
  // segment immediately.
  shmctl(shmid, IPC_RMID, NULL);

  if ((intptr_t)addr == -1) {
     if (warn_on_failure) {
       jio_snprintf(msg, sizeof(msg), "Failed to attach shared memory (errno = %d).", err);
       warning(msg);
     }
     return NULL;
  }

  return addr;
}

static void warn_on_large_pages_failure(char* req_addr, size_t bytes, int error) {
  assert(error == ENOMEM, "Only expect to fail if no memory is available");

  bool warn_on_failure = UseLargePages &&
      (!FLAG_IS_DEFAULT(UseLargePages) ||
       !FLAG_IS_DEFAULT(UseHugeTLBFS) ||
       !FLAG_IS_DEFAULT(LargePageSizeInBytes));

  if (warn_on_failure) {
    char msg[128];
    jio_snprintf(msg, sizeof(msg), "Failed to reserve large pages memory req_addr: "
        PTR_FORMAT " bytes: " SIZE_FORMAT " (errno = %d).", req_addr, bytes, error);
    warning(msg);
  }
}

char* os::Linux::reserve_memory_special_huge_tlbfs_only(size_t bytes, char* req_addr, bool exec) {
  assert(UseLargePages && UseHugeTLBFS, "only for Huge TLBFS large pages");
  assert(is_size_aligned(bytes, os::large_page_size()), "Unaligned size");
  assert(is_ptr_aligned(req_addr, os::large_page_size()), "Unaligned address");

  int prot = exec ? PROT_READ|PROT_WRITE|PROT_EXEC : PROT_READ|PROT_WRITE;
  char* addr = (char*)::mmap(req_addr, bytes, prot,
                             MAP_PRIVATE|MAP_ANONYMOUS|MAP_HUGETLB,
                             -1, 0);

  if (addr == MAP_FAILED) {
    warn_on_large_pages_failure(req_addr, bytes, errno);
    return NULL;
  }

  assert(is_ptr_aligned(addr, os::large_page_size()), "Must be");

  return addr;
}

char* os::Linux::reserve_memory_special_huge_tlbfs_mixed(size_t bytes, size_t alignment, char* req_addr, bool exec) {
  size_t large_page_size = os::large_page_size();

  assert(bytes >= large_page_size, "Shouldn't allocate large pages for small sizes");

  // Allocate small pages.

  char* start;
  if (req_addr != NULL) {
    assert(is_ptr_aligned(req_addr, alignment), "Must be");
    assert(is_size_aligned(bytes, alignment), "Must be");
    start = os::reserve_memory(bytes, req_addr);
    assert(start == NULL || start == req_addr, "Must be");
  } else {
    start = os::reserve_memory_aligned(bytes, alignment);
  }

  if (start == NULL) {
    return NULL;
  }

  assert(is_ptr_aligned(start, alignment), "Must be");

  // os::reserve_memory_special will record this memory area.
  // Need to release it here to prevent overlapping reservations.
  MemTracker::record_virtual_memory_release((address)start, bytes);

  char* end = start + bytes;

  // Find the regions of the allocated chunk that can be promoted to large pages.
  char* lp_start = (char*)align_ptr_up(start, large_page_size);
  char* lp_end   = (char*)align_ptr_down(end, large_page_size);

  size_t lp_bytes = lp_end - lp_start;

  assert(is_size_aligned(lp_bytes, large_page_size), "Must be");

  if (lp_bytes == 0) {
    // The mapped region doesn't even span the start and the end of a large page.
    // Fall back to allocate a non-special area.
    ::munmap(start, end - start);
    return NULL;
  }

  int prot = exec ? PROT_READ|PROT_WRITE|PROT_EXEC : PROT_READ|PROT_WRITE;


  void* result;

  if (start != lp_start) {
    result = ::mmap(start, lp_start - start, prot,
                    MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED,
                    -1, 0);
    if (result == MAP_FAILED) {
      ::munmap(lp_start, end - lp_start);
      return NULL;
    }
  }

  result = ::mmap(lp_start, lp_bytes, prot,
                  MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED|MAP_HUGETLB,
                  -1, 0);
  if (result == MAP_FAILED) {
    warn_on_large_pages_failure(req_addr, bytes, errno);
    // If the mmap above fails, the large pages region will be unmapped and we
    // have regions before and after with small pages. Release these regions.
    //
    // |  mapped  |  unmapped  |  mapped  |
    // ^          ^            ^          ^
    // start      lp_start     lp_end     end
    //
    ::munmap(start, lp_start - start);
    ::munmap(lp_end, end - lp_end);
    return NULL;
  }

  if (lp_end != end) {
      result = ::mmap(lp_end, end - lp_end, prot,
                      MAP_PRIVATE|MAP_ANONYMOUS|MAP_FIXED,
                      -1, 0);
    if (result == MAP_FAILED) {
      ::munmap(start, lp_end - start);
      return NULL;
    }
  }

  return start;
}

char* os::Linux::reserve_memory_special_huge_tlbfs(size_t bytes, size_t alignment, char* req_addr, bool exec) {
  assert(UseLargePages && UseHugeTLBFS, "only for Huge TLBFS large pages");
  assert(is_ptr_aligned(req_addr, alignment), "Must be");
  assert(is_power_of_2(alignment), "Must be");
  assert(is_power_of_2(os::large_page_size()), "Must be");
  assert(bytes >= os::large_page_size(), "Shouldn't allocate large pages for small sizes");

  if (is_size_aligned(bytes, os::large_page_size()) && alignment <= os::large_page_size()) {
    return reserve_memory_special_huge_tlbfs_only(bytes, req_addr, exec);
  } else {
    return reserve_memory_special_huge_tlbfs_mixed(bytes, alignment, req_addr, exec);
  }
}

char* os::reserve_memory_special(size_t bytes, size_t alignment, char* req_addr, bool exec) {
  assert(UseLargePages, "only for large pages");

  char* addr;
  if (UseSHM) {
    addr = os::Linux::reserve_memory_special_shm(bytes, alignment, req_addr, exec);
  } else {
    assert(UseHugeTLBFS, "must be");
    addr = os::Linux::reserve_memory_special_huge_tlbfs(bytes, alignment, req_addr, exec);
  }

  if (addr != NULL) {
    if (UseNUMAInterleaving) {
      numa_make_global(addr, bytes);
    }

    // The memory is committed
    MemTracker::record_virtual_memory_reserve_and_commit((address)addr, bytes, mtNone, CALLER_PC);
  }

  return addr;
}

bool os::Linux::release_memory_special_shm(char* base, size_t bytes) {
  // detaching the SHM segment will also delete it, see reserve_memory_special_shm()
  return shmdt(base) == 0;
}

bool os::Linux::release_memory_special_huge_tlbfs(char* base, size_t bytes) {
  return pd_release_memory(base, bytes);
}

bool os::release_memory_special(char* base, size_t bytes) {
  assert(UseLargePages, "only for large pages");

  MemTracker::Tracker tkr = MemTracker::get_virtual_memory_release_tracker();

  bool res;
  if (UseSHM) {
    res = os::Linux::release_memory_special_shm(base, bytes);
  } else {
    assert(UseHugeTLBFS, "must be");
    res = os::Linux::release_memory_special_huge_tlbfs(base, bytes);
  }

  if (res) {
    tkr.record((address)base, bytes);
  } else {
    tkr.discard();
  }

  return res;
}


size_t os::large_page_size() {
  return _large_page_size;
}

// With SysV SHM the entire memory region must be allocated as shared
// memory.
// HugeTLBFS allows application to commit large page memory on demand.
// However, when committing memory with HugeTLBFS fails, the region
// that was supposed to be committed will lose the old reservation
// and allow other threads to steal that memory region. Because of this
// behavior we can't commit HugeTLBFS memory.
bool os::can_commit_large_page_memory() {
  return UseTransparentHugePages;
}

bool os::can_execute_large_page_memory() {
  return UseTransparentHugePages || UseHugeTLBFS;
}

// Reserve memory at an arbitrary address, only if that area is
// available (and not reserved for something else).

char* os::pd_attempt_reserve_memory_at(size_t bytes, char* requested_addr) {
  const int max_tries = 10;
  char* base[max_tries];
  size_t size[max_tries];
  const size_t gap = 0x000000;

  // Assert only that the size is a multiple of the page size, since
  // that's all that mmap requires, and since that's all we really know
  // about at this low abstraction level.  If we need higher alignment,
  // we can either pass an alignment to this method or verify alignment
  // in one of the methods further up the call chain.  See bug 5044738.
  assert(bytes % os::vm_page_size() == 0, "reserving unexpected size block");

  // Repeatedly allocate blocks until the block is allocated at the
  // right spot. Give up after max_tries. Note that reserve_memory() will
  // automatically update _highest_vm_reserved_address if the call is
  // successful. The variable tracks the highest memory address every reserved
  // by JVM. It is used to detect heap-stack collision if running with
  // fixed-stack LinuxThreads. Because here we may attempt to reserve more
  // space than needed, it could confuse the collision detecting code. To
  // solve the problem, save current _highest_vm_reserved_address and
  // calculate the correct value before return.
  address old_highest = _highest_vm_reserved_address;

  // Linux mmap allows caller to pass an address as hint; give it a try first,
  // if kernel honors the hint then we can return immediately.
  char * addr = anon_mmap(requested_addr, bytes, false);
  if (addr == requested_addr) {
     return requested_addr;
  }

  if (addr != NULL) {
     // mmap() is successful but it fails to reserve at the requested address
     anon_munmap(addr, bytes);
  }

  int i;
  for (i = 0; i < max_tries; ++i) {
    base[i] = reserve_memory(bytes);

    if (base[i] != NULL) {
      // Is this the block we wanted?
      if (base[i] == requested_addr) {
        size[i] = bytes;
        break;
      }

      // Does this overlap the block we wanted? Give back the overlapped
      // parts and try again.

      size_t top_overlap = requested_addr + (bytes + gap) - base[i];
      if (top_overlap >= 0 && top_overlap < bytes) {
        unmap_memory(base[i], top_overlap);
        base[i] += top_overlap;
        size[i] = bytes - top_overlap;
      } else {
        size_t bottom_overlap = base[i] + bytes - requested_addr;
        if (bottom_overlap >= 0 && bottom_overlap < bytes) {
          unmap_memory(requested_addr, bottom_overlap);
          size[i] = bytes - bottom_overlap;
        } else {
          size[i] = bytes;
        }
      }
    }
  }

  // Give back the unused reserved pieces.

  for (int j = 0; j < i; ++j) {
    if (base[j] != NULL) {
      unmap_memory(base[j], size[j]);
    }
  }

  if (i < max_tries) {
    _highest_vm_reserved_address = MAX2(old_highest, (address)requested_addr + bytes);
    return requested_addr;
  } else {
    _highest_vm_reserved_address = old_highest;
    return NULL;
  }
}

size_t os::read(int fd, void *buf, unsigned int nBytes) {
  return ::read(fd, buf, nBytes);
}

// TODO-FIXME: reconcile Solaris' os::sleep with the linux variation.
// Solaris uses poll(), linux uses park().
// Poll() is likely a better choice, assuming that Thread.interrupt()
// generates a SIGUSRx signal. Note that SIGUSR1 can interfere with
// SIGSEGV, see 4355769.

int os::sleep(Thread* thread, jlong millis, bool interruptible) {
  assert(thread == Thread::current(),  "thread consistency check");

  ParkEvent * const slp = thread->_SleepEvent ;
  slp->reset() ;
  OrderAccess::fence() ;

  if (interruptible) {
    jlong prevtime = javaTimeNanos();

    for (;;) {
      if (os::is_interrupted(thread, true)) {
        return OS_INTRPT;
      }

      jlong newtime = javaTimeNanos();

      if (newtime - prevtime < 0) {
        // time moving backwards, should only happen if no monotonic clock
        // not a guarantee() because JVM should not abort on kernel/glibc bugs
        assert(!Linux::supports_monotonic_clock(), "time moving backwards");
      } else {
        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
      }

      if(millis <= 0) {
        return OS_OK;
      }

      prevtime = newtime;

      {
        assert(thread->is_Java_thread(), "sanity check");
        JavaThread *jt = (JavaThread *) thread;
        ThreadBlockInVM tbivm(jt);
        OSThreadWaitState osts(jt->osthread(), false /* not Object.wait() */);

        jt->set_suspend_equivalent();
        // cleared by handle_special_suspend_equivalent_condition() or
        // java_suspend_self() via check_and_wait_while_suspended()

        slp->park(millis);

        // were we externally suspended while we were waiting?
        jt->check_and_wait_while_suspended();
      }
    }
  } else {
    OSThreadWaitState osts(thread->osthread(), false /* not Object.wait() */);
    jlong prevtime = javaTimeNanos();

    for (;;) {
      // It'd be nice to avoid the back-to-back javaTimeNanos() calls on
      // the 1st iteration ...
      jlong newtime = javaTimeNanos();

      if (newtime - prevtime < 0) {
        // time moving backwards, should only happen if no monotonic clock
        // not a guarantee() because JVM should not abort on kernel/glibc bugs
        assert(!Linux::supports_monotonic_clock(), "time moving backwards");
      } else {
        millis -= (newtime - prevtime) / NANOSECS_PER_MILLISEC;
      }

      if(millis <= 0) break ;

      prevtime = newtime;
      slp->park(millis);
    }
    return OS_OK ;
  }
}

//
// Short sleep, direct OS call.
//
// Note: certain versions of Linux CFS scheduler (since 2.6.23) do not guarantee
// sched_yield(2) will actually give up the CPU:
//
//   * Alone on this pariticular CPU, keeps running.
//   * Before the introduction of "skip_buddy" with "compat_yield" disabled
//     (pre 2.6.39).
//
// So calling this with 0 is an alternative.
//
void os::naked_short_sleep(jlong ms) {
  struct timespec req;

  assert(ms < 1000, "Un-interruptable sleep, short time use only");
  req.tv_sec = 0;
  if (ms > 0) {
    req.tv_nsec = (ms % 1000) * 1000000;
  }
  else {
    req.tv_nsec = 1;
  }

  nanosleep(&req, NULL);

  return;
}

// Sleep forever; naked call to OS-specific sleep; use with CAUTION
void os::infinite_sleep() {
  while (true) {    // sleep forever ...
    ::sleep(100);   // ... 100 seconds at a time
  }
}

// Used to convert frequent JVM_Yield() to nops
bool os::dont_yield() {
  return DontYieldALot;
}

void os::yield() {
  sched_yield();
}

os::YieldResult os::NakedYield() { sched_yield(); return os::YIELD_UNKNOWN ;}

void os::yield_all(int attempts) {
  // Yields to all threads, including threads with lower priorities
  // Threads on Linux are all with same priority. The Solaris style
  // os::yield_all() with nanosleep(1ms) is not necessary.
  sched_yield();
}

// Called from the tight loops to possibly influence time-sharing heuristics
void os::loop_breaker(int attempts) {
  os::yield_all(attempts);
}

////////////////////////////////////////////////////////////////////////////////
// thread priority support

// Note: Normal Linux applications are run with SCHED_OTHER policy. SCHED_OTHER
// only supports dynamic priority, static priority must be zero. For real-time
// applications, Linux supports SCHED_RR which allows static priority (1-99).
// However, for large multi-threaded applications, SCHED_RR is not only slower
// than SCHED_OTHER, but also very unstable (my volano tests hang hard 4 out
// of 5 runs - Sep 2005).
//
// The following code actually changes the niceness of kernel-thread/LWP. It
// has an assumption that setpriority() only modifies one kernel-thread/LWP,
// not the entire user process, and user level threads are 1:1 mapped to kernel
// threads. It has always been the case, but could change in the future. For
// this reason, the code should not be used as default (ThreadPriorityPolicy=0).
// It is only used when ThreadPriorityPolicy=1 and requires root privilege.

int os::java_to_os_priority[CriticalPriority + 1] = {
  19,              // 0 Entry should never be used

   4,              // 1 MinPriority
   3,              // 2
   2,              // 3

   1,              // 4
   0,              // 5 NormPriority
  -1,              // 6

  -2,              // 7
  -3,              // 8
  -4,              // 9 NearMaxPriority

  -5,              // 10 MaxPriority

  -5               // 11 CriticalPriority
};

static int prio_init() {
  if (ThreadPriorityPolicy == 1) {
    // Only root can raise thread priority. Don't allow ThreadPriorityPolicy=1
    // if effective uid is not root. Perhaps, a more elegant way of doing
    // this is to test CAP_SYS_NICE capability, but that will require libcap.so
    if (geteuid() != 0) {
      if (!FLAG_IS_DEFAULT(ThreadPriorityPolicy)) {
        warning("-XX:ThreadPriorityPolicy requires root privilege on Linux");
      }
      ThreadPriorityPolicy = 0;
    }
  }
  if (UseCriticalJavaThreadPriority) {
    os::java_to_os_priority[MaxPriority] = os::java_to_os_priority[CriticalPriority];
  }
  return 0;
}

OSReturn os::set_native_priority(Thread* thread, int newpri) {
  if ( !UseThreadPriorities || ThreadPriorityPolicy == 0 ) return OS_OK;

  int ret = setpriority(PRIO_PROCESS, thread->osthread()->thread_id(), newpri);
  return (ret == 0) ? OS_OK : OS_ERR;
}

OSReturn os::get_native_priority(const Thread* const thread, int *priority_ptr) {
  if ( !UseThreadPriorities || ThreadPriorityPolicy == 0 ) {
    *priority_ptr = java_to_os_priority[NormPriority];
    return OS_OK;
  }

  errno = 0;
  *priority_ptr = getpriority(PRIO_PROCESS, thread->osthread()->thread_id());
  return (*priority_ptr != -1 || errno == 0 ? OS_OK : OS_ERR);
}

// Hint to the underlying OS that a task switch would not be good.
// Void return because it's a hint and can fail.
void os::hint_no_preempt() {}

////////////////////////////////////////////////////////////////////////////////
// suspend/resume support

//  the low-level signal-based suspend/resume support is a remnant from the
//  old VM-suspension that used to be for java-suspension, safepoints etc,
//  within hotspot. Now there is a single use-case for this:
//    - calling get_thread_pc() on the VMThread by the flat-profiler task
//      that runs in the watcher thread.
//  The remaining code is greatly simplified from the more general suspension
//  code that used to be used.
//
//  The protocol is quite simple:
//  - suspend:
//      - sends a signal to the target thread
//      - polls the suspend state of the osthread using a yield loop
//      - target thread signal handler (SR_handler) sets suspend state
//        and blocks in sigsuspend until continued
//  - resume:
//      - sets target osthread state to continue
//      - sends signal to end the sigsuspend loop in the SR_handler
//
//  Note that the SR_lock plays no role in this suspend/resume protocol.
//

static void resume_clear_context(OSThread *osthread) {
  osthread->set_ucontext(NULL);
  osthread->set_siginfo(NULL);
}

static void suspend_save_context(OSThread *osthread, siginfo_t* siginfo, ucontext_t* context) {
  osthread->set_ucontext(context);
  osthread->set_siginfo(siginfo);
}

//
// Handler function invoked when a thread's execution is suspended or
// resumed. We have to be careful that only async-safe functions are
// called here (Note: most pthread functions are not async safe and
// should be avoided.)
//
// Note: sigwait() is a more natural fit than sigsuspend() from an
// interface point of view, but sigwait() prevents the signal hander
// from being run. libpthread would get very confused by not having
// its signal handlers run and prevents sigwait()'s use with the
// mutex granting granting signal.
//
// Currently only ever called on the VMThread and JavaThreads (PC sampling)
//
static void SR_handler(int sig, siginfo_t* siginfo, ucontext_t* context) {
  // Save and restore errno to avoid confusing native code with EINTR
  // after sigsuspend.
  int old_errno = errno;

  Thread* thread = Thread::current();
  OSThread* osthread = thread->osthread();
  assert(thread->is_VM_thread() || thread->is_Java_thread(), "Must be VMThread or JavaThread");

  os::SuspendResume::State current = osthread->sr.state();
  if (current == os::SuspendResume::SR_SUSPEND_REQUEST) {
    suspend_save_context(osthread, siginfo, context);

    // attempt to switch the state, we assume we had a SUSPEND_REQUEST
    os::SuspendResume::State state = osthread->sr.suspended();
    if (state == os::SuspendResume::SR_SUSPENDED) {
      sigset_t suspend_set;  // signals for sigsuspend()

      // get current set of blocked signals and unblock resume signal
      pthread_sigmask(SIG_BLOCK, NULL, &suspend_set);
      sigdelset(&suspend_set, SR_signum);

      sr_semaphore.signal();
      // wait here until we are resumed
      while (1) {
        sigsuspend(&suspend_set);

        os::SuspendResume::State result = osthread->sr.running();
        if (result == os::SuspendResume::SR_RUNNING) {
          sr_semaphore.signal();
          break;
        }
      }

    } else if (state == os::SuspendResume::SR_RUNNING) {
      // request was cancelled, continue
    } else {
      ShouldNotReachHere();
    }

    resume_clear_context(osthread);
  } else if (current == os::SuspendResume::SR_RUNNING) {
    // request was cancelled, continue
  } else if (current == os::SuspendResume::SR_WAKEUP_REQUEST) {
    // ignore
  } else {
    // ignore
  }

  errno = old_errno;
}


static int SR_initialize() {
  struct sigaction act;
  char *s;
  /* Get signal number to use for suspend/resume */
  if ((s = ::getenv("_JAVA_SR_SIGNUM")) != 0) {
    int sig = ::strtol(s, 0, 10);
    if (sig > 0 || sig < _NSIG) {
        SR_signum = sig;
    }
  }

  assert(SR_signum > SIGSEGV && SR_signum > SIGBUS,
        "SR_signum must be greater than max(SIGSEGV, SIGBUS), see 4355769");

  sigemptyset(&SR_sigset);
  sigaddset(&SR_sigset, SR_signum);

  /* Set up signal handler for suspend/resume */
  act.sa_flags = SA_RESTART|SA_SIGINFO;
  act.sa_handler = (void (*)(int)) SR_handler;

  // SR_signum is blocked by default.
  // 4528190 - We also need to block pthread restart signal (32 on all
  // supported Linux platforms). Note that LinuxThreads need to block
  // this signal for all threads to work properly. So we don't have
  // to use hard-coded signal number when setting up the mask.
  pthread_sigmask(SIG_BLOCK, NULL, &act.sa_mask);

  if (sigaction(SR_signum, &act, 0) == -1) {
    return -1;
  }

  // Save signal flag
  os::Linux::set_our_sigflags(SR_signum, act.sa_flags);
  return 0;
}

static int SR_finalize() {
  return 0;
}

static int sr_notify(OSThread* osthread) {
  int status = pthread_kill(osthread->pthread_id(), SR_signum);
  assert_status(status == 0, status, "pthread_kill");
  return status;
}

// "Randomly" selected value for how long we want to spin
// before bailing out on suspending a thread, also how often
// we send a signal to a thread we want to resume
static const int RANDOMLY_LARGE_INTEGER = 1000000;
static const int RANDOMLY_LARGE_INTEGER2 = 100;

// returns true on success and false on error - really an error is fatal
// but this seems the normal response to library errors
static bool do_suspend(OSThread* osthread) {
  assert(osthread->sr.is_running(), "thread should be running");
  assert(!sr_semaphore.trywait(), "semaphore has invalid state");

  // mark as suspended and send signal
  if (osthread->sr.request_suspend() != os::SuspendResume::SR_SUSPEND_REQUEST) {
    // failed to switch, state wasn't running?
    ShouldNotReachHere();
    return false;
  }

  if (sr_notify(osthread) != 0) {
    ShouldNotReachHere();
  }

  // managed to send the signal and switch to SUSPEND_REQUEST, now wait for SUSPENDED
  while (true) {
    if (sr_semaphore.timedwait(0, 2 * NANOSECS_PER_MILLISEC)) {
      break;
    } else {
      // timeout
      os::SuspendResume::State cancelled = osthread->sr.cancel_suspend();
      if (cancelled == os::SuspendResume::SR_RUNNING) {
        return false;
      } else if (cancelled == os::SuspendResume::SR_SUSPENDED) {
        // make sure that we consume the signal on the semaphore as well
        sr_semaphore.wait();
        break;
      } else {
        ShouldNotReachHere();
        return false;
      }
    }
  }

  guarantee(osthread->sr.is_suspended(), "Must be suspended");
  return true;
}

static void do_resume(OSThread* osthread) {
  assert(osthread->sr.is_suspended(), "thread should be suspended");
  assert(!sr_semaphore.trywait(), "invalid semaphore state");

  if (osthread->sr.request_wakeup() != os::SuspendResume::SR_WAKEUP_REQUEST) {
    // failed to switch to WAKEUP_REQUEST
    ShouldNotReachHere();
    return;
  }

  while (true) {
    if (sr_notify(osthread) == 0) {
      if (sr_semaphore.timedwait(0, 2 * NANOSECS_PER_MILLISEC)) {
        if (osthread->sr.is_running()) {
          return;
        }
      }
    } else {
      ShouldNotReachHere();
    }
  }

  guarantee(osthread->sr.is_running(), "Must be running!");
}

////////////////////////////////////////////////////////////////////////////////
// interrupt support

void os::interrupt(Thread* thread) {
  assert(Thread::current() == thread || Threads_lock->owned_by_self(),
    "possibility of dangling Thread pointer");

  OSThread* osthread = thread->osthread();

  if (!osthread->interrupted()) {
    osthread->set_interrupted(true);
    // More than one thread can get here with the same value of osthread,
    // resulting in multiple notifications.  We do, however, want the store
    // to interrupted() to be visible to other threads before we execute unpark().
    OrderAccess::fence();
    ParkEvent * const slp = thread->_SleepEvent ;
    if (slp != NULL) slp->unpark() ;
  }

  // For JSR166. Unpark even if interrupt status already was set
  if (thread->is_Java_thread())
    ((JavaThread*)thread)->parker()->unpark();

  ParkEvent * ev = thread->_ParkEvent ;
  if (ev != NULL) ev->unpark() ;

}

bool os::is_interrupted(Thread* thread, bool clear_interrupted) {
  assert(Thread::current() == thread || Threads_lock->owned_by_self(),
    "possibility of dangling Thread pointer");

  OSThread* osthread = thread->osthread();

  bool interrupted = osthread->interrupted();

  if (interrupted && clear_interrupted) {
    osthread->set_interrupted(false);
    // consider thread->_SleepEvent->reset() ... optional optimization
  }

  return interrupted;
}

///////////////////////////////////////////////////////////////////////////////////
// signal handling (except suspend/resume)

// This routine may be used by user applications as a "hook" to catch signals.
// The user-defined signal handler must pass unrecognized signals to this
// routine, and if it returns true (non-zero), then the signal handler must
// return immediately.  If the flag "abort_if_unrecognized" is true, then this
// routine will never retun false (zero), but instead will execute a VM panic
// routine kill the process.
//
// If this routine returns false, it is OK to call it again.  This allows
// the user-defined signal handler to perform checks either before or after
// the VM performs its own checks.  Naturally, the user code would be making
// a serious error if it tried to handle an exception (such as a null check
// or breakpoint) that the VM was generating for its own correct operation.
//
// This routine may recognize any of the following kinds of signals:
//    SIGBUS, SIGSEGV, SIGILL, SIGFPE, SIGQUIT, SIGPIPE, SIGXFSZ, SIGUSR1.
// It should be consulted by handlers for any of those signals.
//
// The caller of this routine must pass in the three arguments supplied
// to the function referred to in the "sa_sigaction" (not the "sa_handler")
// field of the structure passed to sigaction().  This routine assumes that
// the sa_flags field passed to sigaction() includes SA_SIGINFO and SA_RESTART.
//
// Note that the VM will print warnings if it detects conflicting signal
// handlers, unless invoked with the option "-XX:+AllowUserSignalHandlers".
//
extern "C" JNIEXPORT int
JVM_handle_linux_signal(int signo, siginfo_t* siginfo,
                        void* ucontext, int abort_if_unrecognized);

void signalHandler(int sig, siginfo_t* info, void* uc) {
  assert(info != NULL && uc != NULL, "it must be old kernel");
  JVM_handle_linux_signal(sig, info, uc, true);
}


// This boolean allows users to forward their own non-matching signals
// to JVM_handle_linux_signal, harmlessly.
bool os::Linux::signal_handlers_are_installed = false;

// For signal-chaining
struct sigaction os::Linux::sigact[MAXSIGNUM];
unsigned int os::Linux::sigs = 0;
bool os::Linux::libjsig_is_loaded = false;
typedef struct sigaction *(*get_signal_t)(int);
get_signal_t os::Linux::get_signal_action = NULL;

struct sigaction* os::Linux::get_chained_signal_action(int sig) {
  struct sigaction *actp = NULL;

  if (libjsig_is_loaded) {
    // Retrieve the old signal handler from libjsig
    actp = (*get_signal_action)(sig);
  }
  if (actp == NULL) {
    // Retrieve the preinstalled signal handler from jvm
    actp = get_preinstalled_handler(sig);
  }

  return actp;
}

static bool call_chained_handler(struct sigaction *actp, int sig,
                                 siginfo_t *siginfo, void *context) {
  // Call the old signal handler
  if (actp->sa_handler == SIG_DFL) {
    // It's more reasonable to let jvm treat it as an unexpected exception
    // instead of taking the default action.
    return false;
  } else if (actp->sa_handler != SIG_IGN) {
    if ((actp->sa_flags & SA_NODEFER) == 0) {
      // automaticlly block the signal
      sigaddset(&(actp->sa_mask), sig);
    }

    sa_handler_t hand;
    sa_sigaction_t sa;
    bool siginfo_flag_set = (actp->sa_flags & SA_SIGINFO) != 0;
    // retrieve the chained handler
    if (siginfo_flag_set) {
      sa = actp->sa_sigaction;
    } else {
      hand = actp->sa_handler;
    }

    if ((actp->sa_flags & SA_RESETHAND) != 0) {
      actp->sa_handler = SIG_DFL;
    }

    // try to honor the signal mask
    sigset_t oset;
    pthread_sigmask(SIG_SETMASK, &(actp->sa_mask), &oset);

    // call into the chained handler
    if (siginfo_flag_set) {
      (*sa)(sig, siginfo, context);
    } else {
      (*hand)(sig);
    }

    // restore the signal mask
    pthread_sigmask(SIG_SETMASK, &oset, 0);
  }
  // Tell jvm's signal handler the signal is taken care of.
  return true;
}

bool os::Linux::chained_handler(int sig, siginfo_t* siginfo, void* context) {
  bool chained = false;
  // signal-chaining
  if (UseSignalChaining) {
    struct sigaction *actp = get_chained_signal_action(sig);
    if (actp != NULL) {
      chained = call_chained_handler(actp, sig, siginfo, context);
    }
  }
  return chained;
}

struct sigaction* os::Linux::get_preinstalled_handler(int sig) {
  if ((( (unsigned int)1 << sig ) & sigs) != 0) {
    return &sigact[sig];
  }
  return NULL;
}

void os::Linux::save_preinstalled_handler(int sig, struct sigaction& oldAct) {
  assert(sig > 0 && sig < MAXSIGNUM, "vm signal out of expected range");
  sigact[sig] = oldAct;
  sigs |= (unsigned int)1 << sig;
}

// for diagnostic
int os::Linux::sigflags[MAXSIGNUM];

int os::Linux::get_our_sigflags(int sig) {
  assert(sig > 0 && sig < MAXSIGNUM, "vm signal out of expected range");
  return sigflags[sig];
}

void os::Linux::set_our_sigflags(int sig, int flags) {
  assert(sig > 0 && sig < MAXSIGNUM, "vm signal out of expected range");
  sigflags[sig] = flags;
}

void os::Linux::set_signal_handler(int sig, bool set_installed) {
  // Check for overwrite.
  struct sigaction oldAct;
  sigaction(sig, (struct sigaction*)NULL, &oldAct);

  void* oldhand = oldAct.sa_sigaction
                ? CAST_FROM_FN_PTR(void*,  oldAct.sa_sigaction)
                : CAST_FROM_FN_PTR(void*,  oldAct.sa_handler);
  if (oldhand != CAST_FROM_FN_PTR(void*, SIG_DFL) &&
      oldhand != CAST_FROM_FN_PTR(void*, SIG_IGN) &&
      oldhand != CAST_FROM_FN_PTR(void*, (sa_sigaction_t)signalHandler)) {
    if (AllowUserSignalHandlers || !set_installed) {
      // Do not overwrite; user takes responsibility to forward to us.
      return;
    } else if (UseSignalChaining) {
      // save the old handler in jvm
      save_preinstalled_handler(sig, oldAct);
      // libjsig also interposes the sigaction() call below and saves the
      // old sigaction on it own.
    } else {
      fatal(err_msg("Encountered unexpected pre-existing sigaction handler "
                    "%#lx for signal %d.", (long)oldhand, sig));
    }
  }

  struct sigaction sigAct;
  sigfillset(&(sigAct.sa_mask));
  sigAct.sa_handler = SIG_DFL;
  if (!set_installed) {
    sigAct.sa_flags = SA_SIGINFO|SA_RESTART;
  } else {
    sigAct.sa_sigaction = signalHandler;
    sigAct.sa_flags = SA_SIGINFO|SA_RESTART;
  }
  // Save flags, which are set by ours
  assert(sig > 0 && sig < MAXSIGNUM, "vm signal out of expected range");
  sigflags[sig] = sigAct.sa_flags;

  int ret = sigaction(sig, &sigAct, &oldAct);
  assert(ret == 0, "check");

  void* oldhand2  = oldAct.sa_sigaction
                  ? CAST_FROM_FN_PTR(void*, oldAct.sa_sigaction)
                  : CAST_FROM_FN_PTR(void*, oldAct.sa_handler);
  assert(oldhand2 == oldhand, "no concurrent signal handler installation");
}

// install signal handlers for signals that HotSpot needs to
// handle in order to support Java-level exception handling.

void os::Linux::install_signal_handlers() {
  if (!signal_handlers_are_installed) {
    signal_handlers_are_installed = true;

    // signal-chaining
    typedef void (*signal_setting_t)();
    signal_setting_t begin_signal_setting = NULL;
    signal_setting_t end_signal_setting = NULL;
    begin_signal_setting = CAST_TO_FN_PTR(signal_setting_t,
                             dlsym(RTLD_DEFAULT, "JVM_begin_signal_setting"));
    if (begin_signal_setting != NULL) {
      end_signal_setting = CAST_TO_FN_PTR(signal_setting_t,
                             dlsym(RTLD_DEFAULT, "JVM_end_signal_setting"));
      get_signal_action = CAST_TO_FN_PTR(get_signal_t,
                            dlsym(RTLD_DEFAULT, "JVM_get_signal_action"));
      libjsig_is_loaded = true;
      assert(UseSignalChaining, "should enable signal-chaining");
    }
    if (libjsig_is_loaded) {
      // Tell libjsig jvm is setting signal handlers
      (*begin_signal_setting)();
    }

    set_signal_handler(SIGSEGV, true);
    set_signal_handler(SIGPIPE, true);
    set_signal_handler(SIGBUS, true);
    set_signal_handler(SIGILL, true);
    set_signal_handler(SIGFPE, true);
#if defined(PPC64)
    set_signal_handler(SIGTRAP, true);
#endif
    set_signal_handler(SIGXFSZ, true);

    if (libjsig_is_loaded) {
      // Tell libjsig jvm finishes setting signal handlers
      (*end_signal_setting)();
    }

    // We don't activate signal checker if libjsig is in place, we trust ourselves
    // and if UserSignalHandler is installed all bets are off.
    // Log that signal checking is off only if -verbose:jni is specified.
    if (CheckJNICalls) {
      if (libjsig_is_loaded) {
        if (PrintJNIResolving) {
          tty->print_cr("Info: libjsig is activated, all active signal checking is disabled");
        }
        check_signals = false;
      }
      if (AllowUserSignalHandlers) {
        if (PrintJNIResolving) {
          tty->print_cr("Info: AllowUserSignalHandlers is activated, all active signal checking is disabled");
        }
        check_signals = false;
      }
    }
  }
}

// This is the fastest way to get thread cpu time on Linux.
// Returns cpu time (user+sys) for any thread, not only for current.
// POSIX compliant clocks are implemented in the kernels 2.6.16+.
// It might work on 2.6.10+ with a special kernel/glibc patch.
// For reference, please, see IEEE Std 1003.1-2004:
//   http://www.unix.org/single_unix_specification

jlong os::Linux::fast_thread_cpu_time(clockid_t clockid) {
  struct timespec tp;
  int rc = os::Linux::clock_gettime(clockid, &tp);
  assert(rc == 0, "clock_gettime is expected to return 0 code");

  return (tp.tv_sec * NANOSECS_PER_SEC) + tp.tv_nsec;
}

/////
// glibc on Linux platform uses non-documented flag
// to indicate, that some special sort of signal
// trampoline is used.
// We will never set this flag, and we should
// ignore this flag in our diagnostic
#ifdef SIGNIFICANT_SIGNAL_MASK
#undef SIGNIFICANT_SIGNAL_MASK
#endif
#define SIGNIFICANT_SIGNAL_MASK (~0x04000000)

static const char* get_signal_handler_name(address handler,
                                           char* buf, int buflen) {
  int offset;
  bool found = os::dll_address_to_library_name(handler, buf, buflen, &offset);
  if (found) {
    // skip directory names
    const char *p1, *p2;
    p1 = buf;
    size_t len = strlen(os::file_separator());
    while ((p2 = strstr(p1, os::file_separator())) != NULL) p1 = p2 + len;
    jio_snprintf(buf, buflen, "%s+0x%x", p1, offset);
  } else {
    jio_snprintf(buf, buflen, PTR_FORMAT, handler);
  }
  return buf;
}

static void print_signal_handler(outputStream* st, int sig,
                                 char* buf, size_t buflen) {
  struct sigaction sa;

  sigaction(sig, NULL, &sa);

  // See comment for SIGNIFICANT_SIGNAL_MASK define
  sa.sa_flags &= SIGNIFICANT_SIGNAL_MASK;

  st->print("%s: ", os::exception_name(sig, buf, buflen));

  address handler = (sa.sa_flags & SA_SIGINFO)
    ? CAST_FROM_FN_PTR(address, sa.sa_sigaction)
    : CAST_FROM_FN_PTR(address, sa.sa_handler);

  if (handler == CAST_FROM_FN_PTR(address, SIG_DFL)) {
    st->print("SIG_DFL");
  } else if (handler == CAST_FROM_FN_PTR(address, SIG_IGN)) {
    st->print("SIG_IGN");
  } else {
    st->print("[%s]", get_signal_handler_name(handler, buf, buflen));
  }

  st->print(", sa_mask[0]=" PTR32_FORMAT, *(uint32_t*)&sa.sa_mask);

  address rh = VMError::get_resetted_sighandler(sig);
  // May be, handler was resetted by VMError?
  if(rh != NULL) {
    handler = rh;
    sa.sa_flags = VMError::get_resetted_sigflags(sig) & SIGNIFICANT_SIGNAL_MASK;
  }

  st->print(", sa_flags="   PTR32_FORMAT, sa.sa_flags);

  // Check: is it our handler?
  if(handler == CAST_FROM_FN_PTR(address, (sa_sigaction_t)signalHandler) ||
     handler == CAST_FROM_FN_PTR(address, (sa_sigaction_t)SR_handler)) {
    // It is our signal handler
    // check for flags, reset system-used one!
    if((int)sa.sa_flags != os::Linux::get_our_sigflags(sig)) {
      st->print(
                ", flags was changed from " PTR32_FORMAT ", consider using jsig library",
                os::Linux::get_our_sigflags(sig));
    }
  }
  st->cr();
}


#define DO_SIGNAL_CHECK(sig) \
  if (!sigismember(&check_signal_done, sig)) \
    os::Linux::check_signal_handler(sig)

// This method is a periodic task to check for misbehaving JNI applications
// under CheckJNI, we can add any periodic checks here

void os::run_periodic_checks() {

  if (check_signals == false) return;

  // SEGV and BUS if overridden could potentially prevent
  // generation of hs*.log in the event of a crash, debugging
  // such a case can be very challenging, so we absolutely
  // check the following for a good measure:
  DO_SIGNAL_CHECK(SIGSEGV);
  DO_SIGNAL_CHECK(SIGILL);
  DO_SIGNAL_CHECK(SIGFPE);
  DO_SIGNAL_CHECK(SIGBUS);
  DO_SIGNAL_CHECK(SIGPIPE);
  DO_SIGNAL_CHECK(SIGXFSZ);
#if defined(PPC64)
  DO_SIGNAL_CHECK(SIGTRAP);
#endif

  // ReduceSignalUsage allows the user to override these handlers
  // see comments at the very top and jvm_solaris.h
  if (!ReduceSignalUsage) {
    DO_SIGNAL_CHECK(SHUTDOWN1_SIGNAL);
    DO_SIGNAL_CHECK(SHUTDOWN2_SIGNAL);
    DO_SIGNAL_CHECK(SHUTDOWN3_SIGNAL);
    DO_SIGNAL_CHECK(BREAK_SIGNAL);
  }

  DO_SIGNAL_CHECK(SR_signum);
  DO_SIGNAL_CHECK(INTERRUPT_SIGNAL);
}

typedef int (*os_sigaction_t)(int, const struct sigaction *, struct sigaction *);

static os_sigaction_t os_sigaction = NULL;

void os::Linux::check_signal_handler(int sig) {
  char buf[O_BUFLEN];
  address jvmHandler = NULL;


  struct sigaction act;
  if (os_sigaction == NULL) {
    // only trust the default sigaction, in case it has been interposed
    os_sigaction = (os_sigaction_t)dlsym(RTLD_DEFAULT, "sigaction");
    if (os_sigaction == NULL) return;
  }

  os_sigaction(sig, (struct sigaction*)NULL, &act);


  act.sa_flags &= SIGNIFICANT_SIGNAL_MASK;

  address thisHandler = (act.sa_flags & SA_SIGINFO)
    ? CAST_FROM_FN_PTR(address, act.sa_sigaction)
    : CAST_FROM_FN_PTR(address, act.sa_handler) ;


  switch(sig) {
  case SIGSEGV:
  case SIGBUS:
  case SIGFPE:
  case SIGPIPE:
  case SIGILL:
  case SIGXFSZ:
    jvmHandler = CAST_FROM_FN_PTR(address, (sa_sigaction_t)signalHandler);
    break;

  case SHUTDOWN1_SIGNAL:
  case SHUTDOWN2_SIGNAL:
  case SHUTDOWN3_SIGNAL:
  case BREAK_SIGNAL:
    jvmHandler = (address)user_handler();
    break;

  case INTERRUPT_SIGNAL:
    jvmHandler = CAST_FROM_FN_PTR(address, SIG_DFL);
    break;

  default:
    if (sig == SR_signum) {
      jvmHandler = CAST_FROM_FN_PTR(address, (sa_sigaction_t)SR_handler);
    } else {
      return;
    }
    break;
  }

  if (thisHandler != jvmHandler) {
    tty->print("Warning: %s handler ", exception_name(sig, buf, O_BUFLEN));
    tty->print("expected:%s", get_signal_handler_name(jvmHandler, buf, O_BUFLEN));
    tty->print_cr("  found:%s", get_signal_handler_name(thisHandler, buf, O_BUFLEN));
    // No need to check this sig any longer
    sigaddset(&check_signal_done, sig);
  } else if(os::Linux::get_our_sigflags(sig) != 0 && (int)act.sa_flags != os::Linux::get_our_sigflags(sig)) {
    tty->print("Warning: %s handler flags ", exception_name(sig, buf, O_BUFLEN));
    tty->print("expected:" PTR32_FORMAT, os::Linux::get_our_sigflags(sig));
    tty->print_cr("  found:" PTR32_FORMAT, act.sa_flags);
    // No need to check this sig any longer
    sigaddset(&check_signal_done, sig);
  }

  // Dump all the signal
  if (sigismember(&check_signal_done, sig)) {
    print_signal_handlers(tty, buf, O_BUFLEN);
  }
}

extern void report_error(char* file_name, int line_no, char* title, char* format, ...);

extern bool signal_name(int signo, char* buf, size_t len);

const char* os::exception_name(int exception_code, char* buf, size_t size) {
  if (0 < exception_code && exception_code <= SIGRTMAX) {
    // signal
    if (!signal_name(exception_code, buf, size)) {
      jio_snprintf(buf, size, "SIG%d", exception_code);
    }
    return buf;
  } else {
    return NULL;
  }
}

// this is called _before_ the most of global arguments have been parsed
void os::init(void) {
  char dummy;   /* used to get a guess on initial stack address */
//  first_hrtime = gethrtime();

  // With LinuxThreads the JavaMain thread pid (primordial thread)
  // is different than the pid of the java launcher thread.
  // So, on Linux, the launcher thread pid is passed to the VM
  // via the sun.java.launcher.pid property.
  // Use this property instead of getpid() if it was correctly passed.
  // See bug 6351349.
  pid_t java_launcher_pid = (pid_t) Arguments::sun_java_launcher_pid();

  _initial_pid = (java_launcher_pid > 0) ? java_launcher_pid : getpid();

  clock_tics_per_sec = sysconf(_SC_CLK_TCK);

  init_random(1234567);

  ThreadCritical::initialize();

  Linux::set_page_size(sysconf(_SC_PAGESIZE));
  if (Linux::page_size() == -1) {
    fatal(err_msg("os_linux.cpp: os::init: sysconf failed (%s)",
                  strerror(errno)));
  }
  init_page_sizes((size_t) Linux::page_size());

  Linux::initialize_system_info();

  // main_thread points to the aboriginal thread
  Linux::_main_thread = pthread_self();

  Linux::clock_init();
  initial_time_count = os::elapsed_counter();

  // pthread_condattr initialization for monotonic clock
  int status;
  pthread_condattr_t* _condattr = os::Linux::condAttr();
  if ((status = pthread_condattr_init(_condattr)) != 0) {
    fatal(err_msg("pthread_condattr_init: %s", strerror(status)));
  }
  // Only set the clock if CLOCK_MONOTONIC is available
  if (Linux::supports_monotonic_clock()) {
    if ((status = pthread_condattr_setclock(_condattr, CLOCK_MONOTONIC)) != 0) {
      if (status == EINVAL) {
        warning("Unable to use monotonic clock with relative timed-waits" \
                " - changes to the time-of-day clock may have adverse affects");
      } else {
        fatal(err_msg("pthread_condattr_setclock: %s", strerror(status)));
      }
    }
  }
  // else it defaults to CLOCK_REALTIME

  pthread_mutex_init(&dl_mutex, NULL);

  // If the pagesize of the VM is greater than 8K determine the appropriate
  // number of initial guard pages.  The user can change this with the
  // command line arguments, if needed.
  if (vm_page_size() > (int)Linux::vm_default_page_size()) {
    StackYellowPages = 1;
    StackRedPages = 1;
    StackShadowPages = round_to((StackShadowPages*Linux::vm_default_page_size()), vm_page_size()) / vm_page_size();
  }
}

// To install functions for atexit system call
extern "C" {
  static void perfMemory_exit_helper() {
    perfMemory_exit();
  }
}

// this is called _after_ the global arguments have been parsed
jint os::init_2(void)
{
  Linux::fast_thread_clock_init();

  // Allocate a single page and mark it as readable for safepoint polling
  address polling_page = (address) ::mmap(NULL, Linux::page_size(), PROT_READ, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
  guarantee( polling_page != MAP_FAILED, "os::init_2: failed to allocate polling page" );

  os::set_polling_page( polling_page );

#ifndef PRODUCT
  if(Verbose && PrintMiscellaneous)
    tty->print("[SafePoint Polling address: " INTPTR_FORMAT "]\n", (intptr_t)polling_page);
#endif

  if (!UseMembar) {
    address mem_serialize_page = (address) ::mmap(NULL, Linux::page_size(), PROT_READ | PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
    guarantee( mem_serialize_page != MAP_FAILED, "mmap Failed for memory serialize page");
    os::set_memory_serialize_page( mem_serialize_page );

#ifndef PRODUCT
    if(Verbose && PrintMiscellaneous)
      tty->print("[Memory Serialize  Page address: " INTPTR_FORMAT "]\n", (intptr_t)mem_serialize_page);
#endif
  }

  // initialize suspend/resume support - must do this before signal_sets_init()
  if (SR_initialize() != 0) {
    perror("SR_initialize failed");
    return JNI_ERR;
  }

  Linux::signal_sets_init();
  Linux::install_signal_handlers();

  // Check minimum allowable stack size for thread creation and to initialize
  // the java system classes, including StackOverflowError - depends on page
  // size.  Add a page for compiler2 recursion in main thread.
  // Add in 2*BytesPerWord times page size to account for VM stack during
  // class initialization depending on 32 or 64 bit VM.
  os::Linux::min_stack_allowed = MAX2(os::Linux::min_stack_allowed,
            (size_t)(StackYellowPages+StackRedPages+StackShadowPages) * Linux::page_size() +
                    (2*BytesPerWord COMPILER2_PRESENT(+1)) * Linux::vm_default_page_size());

  size_t threadStackSizeInBytes = ThreadStackSize * K;
  if (threadStackSizeInBytes != 0 &&
      threadStackSizeInBytes < os::Linux::min_stack_allowed) {
        tty->print_cr("\nThe stack size specified is too small, "
                      "Specify at least %dk",
                      os::Linux::min_stack_allowed/ K);
        return JNI_ERR;
  }

  // Make the stack size a multiple of the page size so that
  // the yellow/red zones can be guarded.
  JavaThread::set_stack_size_at_create(round_to(threadStackSizeInBytes,
        vm_page_size()));

  Linux::capture_initial_stack(JavaThread::stack_size_at_create());

#if defined(IA32)
  workaround_expand_exec_shield_cs_limit();
#endif

  Linux::libpthread_init();
  if (PrintMiscellaneous && (Verbose || WizardMode)) {
     tty->print_cr("[HotSpot is running with %s, %s(%s)]\n",
          Linux::glibc_version(), Linux::libpthread_version(),
          Linux::is_floating_stack() ? "floating stack" : "fixed stack");
  }

  if (UseNUMA) {
    if (!Linux::libnuma_init()) {
      UseNUMA = false;
    } else {
      if ((Linux::numa_max_node() < 1)) {
        // There's only one node(they start from 0), disable NUMA.
        UseNUMA = false;
      }
    }
    // With SHM and HugeTLBFS large pages we cannot uncommit a page, so there's no way
    // we can make the adaptive lgrp chunk resizing work. If the user specified
    // both UseNUMA and UseLargePages (or UseSHM/UseHugeTLBFS) on the command line - warn and
    // disable adaptive resizing.
    if (UseNUMA && UseLargePages && !can_commit_large_page_memory()) {
      if (FLAG_IS_DEFAULT(UseNUMA)) {
        UseNUMA = false;
      } else {
        if (FLAG_IS_DEFAULT(UseLargePages) &&
            FLAG_IS_DEFAULT(UseSHM) &&
            FLAG_IS_DEFAULT(UseHugeTLBFS)) {
          UseLargePages = false;
        } else {
          warning("UseNUMA is not fully compatible with SHM/HugeTLBFS large pages, disabling adaptive resizing");
          UseAdaptiveSizePolicy = false;
          UseAdaptiveNUMAChunkSizing = false;
        }
      }
    }
    if (!UseNUMA && ForceNUMA) {
      UseNUMA = true;
    }
  }

  if (MaxFDLimit) {
    // set the number of file descriptors to max. print out error
    // if getrlimit/setrlimit fails but continue regardless.
    struct rlimit nbr_files;
    int status = getrlimit(RLIMIT_NOFILE, &nbr_files);
    if (status != 0) {
      if (PrintMiscellaneous && (Verbose || WizardMode))
        perror("os::init_2 getrlimit failed");
    } else {
      nbr_files.rlim_cur = nbr_files.rlim_max;
      status = setrlimit(RLIMIT_NOFILE, &nbr_files);
      if (status != 0) {
        if (PrintMiscellaneous && (Verbose || WizardMode))
          perror("os::init_2 setrlimit failed");
      }
    }
  }

  // Initialize lock used to serialize thread creation (see os::create_thread)
  Linux::set_createThread_lock(new Mutex(Mutex::leaf, "createThread_lock", false));

  // at-exit methods are called in the reverse order of their registration.
  // atexit functions are called on return from main or as a result of a
  // call to exit(3C). There can be only 32 of these functions registered
  // and atexit() does not set errno.

  if (PerfAllowAtExitRegistration) {
    // only register atexit functions if PerfAllowAtExitRegistration is set.
    // atexit functions can be delayed until process exit time, which
    // can be problematic for embedded VM situations. Embedded VMs should
    // call DestroyJavaVM() to assure that VM resources are released.

    // note: perfMemory_exit_helper atexit function may be removed in
    // the future if the appropriate cleanup code can be added to the
    // VM_Exit VMOperation's doit method.
    if (atexit(perfMemory_exit_helper) != 0) {
      warning("os::init_2 atexit(perfMemory_exit_helper) failed");
    }
  }

  // initialize thread priority policy
  prio_init();

  return JNI_OK;
}

// this is called at the end of vm_initialization
void os::init_3(void) {
#ifdef JAVASE_EMBEDDED
  // Start the MemNotifyThread
  if (LowMemoryProtection) {
    MemNotifyThread::start();
  }
  return;
#endif
}

// Mark the polling page as unreadable
void os::make_polling_page_unreadable(void) {
  if( !guard_memory((char*)_polling_page, Linux::page_size()) )
    fatal("Could not disable polling page");
};

// Mark the polling page as readable
void os::make_polling_page_readable(void) {
  if( !linux_mprotect((char *)_polling_page, Linux::page_size(), PROT_READ)) {
    fatal("Could not enable polling page");
  }
};

int os::active_processor_count() {
  // Linux doesn't yet have a (official) notion of processor sets,
  // so just return the number of online processors.
  int online_cpus = ::sysconf(_SC_NPROCESSORS_ONLN);
  assert(online_cpus > 0 && online_cpus <= processor_count(), "sanity check");
  return online_cpus;
}

void os::set_native_thread_name(const char *name) {
  // Not yet implemented.
  return;
}

bool os::distribute_processes(uint length, uint* distribution) {
  // Not yet implemented.
  return false;
}

bool os::bind_to_processor(uint processor_id) {
  // Not yet implemented.
  return false;
}

///

void os::SuspendedThreadTask::internal_do_task() {
  if (do_suspend(_thread->osthread())) {
    SuspendedThreadTaskContext context(_thread, _thread->osthread()->ucontext());
    do_task(context);
    do_resume(_thread->osthread());
  }
}

class PcFetcher : public os::SuspendedThreadTask {
public:
  PcFetcher(Thread* thread) : os::SuspendedThreadTask(thread) {}
  ExtendedPC result();
protected:
  void do_task(const os::SuspendedThreadTaskContext& context);
private:
  ExtendedPC _epc;
};

ExtendedPC PcFetcher::result() {
  guarantee(is_done(), "task is not done yet.");
  return _epc;
}

void PcFetcher::do_task(const os::SuspendedThreadTaskContext& context) {
  Thread* thread = context.thread();
  OSThread* osthread = thread->osthread();
  if (osthread->ucontext() != NULL) {
    _epc = os::Linux::ucontext_get_pc((ucontext_t *) context.ucontext());
  } else {
    // NULL context is unexpected, double-check this is the VMThread
    guarantee(thread->is_VM_thread(), "can only be called for VMThread");
  }
}

// Suspends the target using the signal mechanism and then grabs the PC before
// resuming the target. Used by the flat-profiler only
ExtendedPC os::get_thread_pc(Thread* thread) {
  // Make sure that it is called by the watcher for the VMThread
  assert(Thread::current()->is_Watcher_thread(), "Must be watcher");
  assert(thread->is_VM_thread(), "Can only be called for VMThread");

  PcFetcher fetcher(thread);
  fetcher.run();
  return fetcher.result();
}

int os::Linux::safe_cond_timedwait(pthread_cond_t *_cond, pthread_mutex_t *_mutex, const struct timespec *_abstime)
{
   if (is_NPTL()) {
      return pthread_cond_timedwait(_cond, _mutex, _abstime);
   } else {
#ifndef IA64
      // 6292965: LinuxThreads pthread_cond_timedwait() resets FPU control
      // word back to default 64bit precision if condvar is signaled. Java
      // wants 53bit precision.  Save and restore current value.
      int fpu = get_fpu_control_word();
#endif // IA64
      int status = pthread_cond_timedwait(_cond, _mutex, _abstime);
#ifndef IA64
      set_fpu_control_word(fpu);
#endif // IA64
      return status;
   }
}

////////////////////////////////////////////////////////////////////////////////
// debug support

static address same_page(address x, address y) {
  intptr_t page_bits = -os::vm_page_size();
  if ((intptr_t(x) & page_bits) == (intptr_t(y) & page_bits))
    return x;
  else if (x > y)
    return (address)(intptr_t(y) | ~page_bits) + 1;
  else
    return (address)(intptr_t(y) & page_bits);
}

bool os::find(address addr, outputStream* st) {
  Dl_info dlinfo;
  memset(&dlinfo, 0, sizeof(dlinfo));
  if (dladdr(addr, &dlinfo) != 0) {
    st->print(PTR_FORMAT ": ", addr);
    if (dlinfo.dli_sname != NULL && dlinfo.dli_saddr != NULL) {
      st->print("%s+%#x", dlinfo.dli_sname,
                 addr - (intptr_t)dlinfo.dli_saddr);
    } else if (dlinfo.dli_fbase != NULL) {
      st->print("<offset %#x>", addr - (intptr_t)dlinfo.dli_fbase);
    } else {
      st->print("<absolute address>");
    }
    if (dlinfo.dli_fname != NULL) {
      st->print(" in %s", dlinfo.dli_fname);
    }
    if (dlinfo.dli_fbase != NULL) {
      st->print(" at " PTR_FORMAT, dlinfo.dli_fbase);
    }
    st->cr();

    if (Verbose) {
      // decode some bytes around the PC
      address begin = same_page(addr-40, addr);
      address end   = same_page(addr+40, addr);
      address       lowest = (address) dlinfo.dli_sname;
      if (!lowest)  lowest = (address) dlinfo.dli_fbase;
      if (begin < lowest)  begin = lowest;
      Dl_info dlinfo2;
      if (dladdr(end, &dlinfo2) != 0 && dlinfo2.dli_saddr != dlinfo.dli_saddr
          && end > dlinfo2.dli_saddr && dlinfo2.dli_saddr > begin)
        end = (address) dlinfo2.dli_saddr;
      Disassembler::decode(begin, end, st);
    }
    return true;
  }
  return false;
}

////////////////////////////////////////////////////////////////////////////////
// misc

// This does not do anything on Linux. This is basically a hook for being
// able to use structured exception handling (thread-local exception filters)
// on, e.g., Win32.
void
os::os_exception_wrapper(java_call_t f, JavaValue* value, methodHandle* method,
                         JavaCallArguments* args, Thread* thread) {
  f(value, method, args, thread);
}

void os::print_statistics() {
}

int os::message_box(const char* title, const char* message) {
  int i;
  fdStream err(defaultStream::error_fd());
  for (i = 0; i < 78; i++) err.print_raw("=");
  err.cr();
  err.print_raw_cr(title);
  for (i = 0; i < 78; i++) err.print_raw("-");
  err.cr();
  err.print_raw_cr(message);
  for (i = 0; i < 78; i++) err.print_raw("=");
  err.cr();

  char buf[16];
  // Prevent process from exiting upon "read error" without consuming all CPU
  while (::read(0, buf, sizeof(buf)) <= 0) { ::sleep(100); }

  return buf[0] == 'y' || buf[0] == 'Y';
}

int os::stat(const char *path, struct stat *sbuf) {
  char pathbuf[MAX_PATH];
  if (strlen(path) > MAX_PATH - 1) {
    errno = ENAMETOOLONG;
    return -1;
  }
  os::native_path(strcpy(pathbuf, path));
  return ::stat(pathbuf, sbuf);
}

bool os::check_heap(bool force) {
  return true;
}

int local_vsnprintf(char* buf, size_t count, const char* format, va_list args) {
  return ::vsnprintf(buf, count, format, args);
}

// Is a (classpath) directory empty?
bool os::dir_is_empty(const char* path) {
  DIR *dir = NULL;
  struct dirent *ptr;

  dir = opendir(path);
  if (dir == NULL) return true;

  /* Scan the directory */
  bool result = true;
  char buf[sizeof(struct dirent) + MAX_PATH];
  while (result && (ptr = ::readdir(dir)) != NULL) {
    if (strcmp(ptr->d_name, ".") != 0 && strcmp(ptr->d_name, "..") != 0) {
      result = false;
    }
  }
  closedir(dir);
  return result;
}

// This code originates from JDK's sysOpen and open64_w
// from src/solaris/hpi/src/system_md.c

#ifndef O_DELETE
#define O_DELETE 0x10000
#endif

// Open a file. Unlink the file immediately after open returns
// if the specified oflag has the O_DELETE flag set.
// O_DELETE is used only in j2se/src/share/native/java/util/zip/ZipFile.c

int os::open(const char *path, int oflag, int mode) {

  if (strlen(path) > MAX_PATH - 1) {
    errno = ENAMETOOLONG;
    return -1;
  }
  int fd;
  int o_delete = (oflag & O_DELETE);
  oflag = oflag & ~O_DELETE;

  fd = ::open64(path, oflag, mode);
  if (fd == -1) return -1;

  //If the open succeeded, the file might still be a directory
  {
    struct stat64 buf64;
    int ret = ::fstat64(fd, &buf64);
    int st_mode = buf64.st_mode;

    if (ret != -1) {
      if ((st_mode & S_IFMT) == S_IFDIR) {
        errno = EISDIR;
        ::close(fd);
        return -1;
      }
    } else {
      ::close(fd);
      return -1;
    }
  }

    /*
     * All file descriptors that are opened in the JVM and not
     * specifically destined for a subprocess should have the
     * close-on-exec flag set.  If we don't set it, then careless 3rd
     * party native code might fork and exec without closing all
     * appropriate file descriptors (e.g. as we do in closeDescriptors in
     * UNIXProcess.c), and this in turn might:
     *
     * - cause end-of-file to fail to be detected on some file
     *   descriptors, resulting in mysterious hangs, or
     *
     * - might cause an fopen in the subprocess to fail on a system
     *   suffering from bug 1085341.
     *
     * (Yes, the default setting of the close-on-exec flag is a Unix
     * design flaw)
     *
     * See:
     * 1085341: 32-bit stdio routines should support file descriptors >255
     * 4843136: (process) pipe file descriptor from Runtime.exec not being closed
     * 6339493: (process) Runtime.exec does not close all file descriptors on Solaris 9
     */
#ifdef FD_CLOEXEC
    {
        int flags = ::fcntl(fd, F_GETFD);
        if (flags != -1)
            ::fcntl(fd, F_SETFD, flags | FD_CLOEXEC);
    }
#endif

  if (o_delete != 0) {
    ::unlink(path);
  }
  return fd;
}


// create binary file, rewriting existing file if required
int os::create_binary_file(const char* path, bool rewrite_existing) {
  int oflags = O_WRONLY | O_CREAT;
  if (!rewrite_existing) {
    oflags |= O_EXCL;
  }
  return ::open64(path, oflags, S_IREAD | S_IWRITE);
}

// return current position of file pointer
jlong os::current_file_offset(int fd) {
  return (jlong)::lseek64(fd, (off64_t)0, SEEK_CUR);
}

// move file pointer to the specified offset
jlong os::seek_to_file_offset(int fd, jlong offset) {
  return (jlong)::lseek64(fd, (off64_t)offset, SEEK_SET);
}

// This code originates from JDK's sysAvailable
// from src/solaris/hpi/src/native_threads/src/sys_api_td.c

int os::available(int fd, jlong *bytes) {
  jlong cur, end;
  int mode;
  struct stat64 buf64;

  if (::fstat64(fd, &buf64) >= 0) {
    mode = buf64.st_mode;
    if (S_ISCHR(mode) || S_ISFIFO(mode) || S_ISSOCK(mode)) {
      /*
      * XXX: is the following call interruptible? If so, this might
      * need to go through the INTERRUPT_IO() wrapper as for other
      * blocking, interruptible calls in this file.
      */
      int n;
      if (::ioctl(fd, FIONREAD, &n) >= 0) {
        *bytes = n;
        return 1;
      }
    }
  }
  if ((cur = ::lseek64(fd, 0L, SEEK_CUR)) == -1) {
    return 0;
  } else if ((end = ::lseek64(fd, 0L, SEEK_END)) == -1) {
    return 0;
  } else if (::lseek64(fd, cur, SEEK_SET) == -1) {
    return 0;
  }
  *bytes = end - cur;
  return 1;
}

int os::socket_available(int fd, jint *pbytes) {
  // Linux doc says EINTR not returned, unlike Solaris
  int ret = ::ioctl(fd, FIONREAD, pbytes);

  //%% note ioctl can return 0 when successful, JVM_SocketAvailable
  // is expected to return 0 on failure and 1 on success to the jdk.
  return (ret < 0) ? 0 : 1;
}

// Map a block of memory.
char* os::pd_map_memory(int fd, const char* file_name, size_t file_offset,
                     char *addr, size_t bytes, bool read_only,
                     bool allow_exec) {
  int prot;
  int flags = MAP_PRIVATE;

  if (read_only) {
    prot = PROT_READ;
  } else {
    prot = PROT_READ | PROT_WRITE;
  }

  if (allow_exec) {
    prot |= PROT_EXEC;
  }

  if (addr != NULL) {
    flags |= MAP_FIXED;
  }

  char* mapped_address = (char*)mmap(addr, (size_t)bytes, prot, flags,
                                     fd, file_offset);
  if (mapped_address == MAP_FAILED) {
    return NULL;
  }
  return mapped_address;
}


// Remap a block of memory.
char* os::pd_remap_memory(int fd, const char* file_name, size_t file_offset,
                       char *addr, size_t bytes, bool read_only,
                       bool allow_exec) {
  // same as map_memory() on this OS
  return os::map_memory(fd, file_name, file_offset, addr, bytes, read_only,
                        allow_exec);
}


// Unmap a block of memory.
bool os::pd_unmap_memory(char* addr, size_t bytes) {
  return munmap(addr, bytes) == 0;
}

static jlong slow_thread_cpu_time(Thread *thread, bool user_sys_cpu_time);

static clockid_t thread_cpu_clockid(Thread* thread) {
  pthread_t tid = thread->osthread()->pthread_id();
  clockid_t clockid;

  // Get thread clockid
  int rc = os::Linux::pthread_getcpuclockid(tid, &clockid);
  assert(rc == 0, "pthread_getcpuclockid is expected to return 0 code");
  return clockid;
}

// current_thread_cpu_time(bool) and thread_cpu_time(Thread*, bool)
// are used by JVM M&M and JVMTI to get user+sys or user CPU time
// of a thread.
//
// current_thread_cpu_time() and thread_cpu_time(Thread*) returns
// the fast estimate available on the platform.

jlong os::current_thread_cpu_time() {
  if (os::Linux::supports_fast_thread_cpu_time()) {
    return os::Linux::fast_thread_cpu_time(CLOCK_THREAD_CPUTIME_ID);
  } else {
    // return user + sys since the cost is the same
    return slow_thread_cpu_time(Thread::current(), true /* user + sys */);
  }
}

jlong os::thread_cpu_time(Thread* thread) {
  // consistent with what current_thread_cpu_time() returns
  if (os::Linux::supports_fast_thread_cpu_time()) {
    return os::Linux::fast_thread_cpu_time(thread_cpu_clockid(thread));
  } else {
    return slow_thread_cpu_time(thread, true /* user + sys */);
  }
}

jlong os::current_thread_cpu_time(bool user_sys_cpu_time) {
  if (user_sys_cpu_time && os::Linux::supports_fast_thread_cpu_time()) {
    return os::Linux::fast_thread_cpu_time(CLOCK_THREAD_CPUTIME_ID);
  } else {
    return slow_thread_cpu_time(Thread::current(), user_sys_cpu_time);
  }
}

jlong os::thread_cpu_time(Thread *thread, bool user_sys_cpu_time) {
  if (user_sys_cpu_time && os::Linux::supports_fast_thread_cpu_time()) {
    return os::Linux::fast_thread_cpu_time(thread_cpu_clockid(thread));
  } else {
    return slow_thread_cpu_time(thread, user_sys_cpu_time);
  }
}

//
//  -1 on error.
//

static jlong slow_thread_cpu_time(Thread *thread, bool user_sys_cpu_time) {
  static bool proc_pid_cpu_avail = true;
  static bool proc_task_unchecked = true;
  static const char *proc_stat_path = "/proc/%d/stat";
  pid_t  tid = thread->osthread()->thread_id();
  int i;
  char *s;
  char stat[2048];
  int statlen;
  char proc_name[64];
  int count;
  long sys_time, user_time;
  char string[64];
  char cdummy;
  int idummy;
  long ldummy;
  FILE *fp;

  // We first try accessing /proc/<pid>/cpu since this is faster to
  // process.  If this file is not present (linux kernels 2.5 and above)
  // then we open /proc/<pid>/stat.
  if ( proc_pid_cpu_avail ) {
    sprintf(proc_name, "/proc/%d/cpu", tid);
    fp =  fopen(proc_name, "r");
    if ( fp != NULL ) {
      count = fscanf( fp, "%s %lu %lu\n", string, &user_time, &sys_time);
      fclose(fp);
      if ( count != 3 ) return -1;

      if (user_sys_cpu_time) {
        return ((jlong)sys_time + (jlong)user_time) * (1000000000 / clock_tics_per_sec);
      } else {
        return (jlong)user_time * (1000000000 / clock_tics_per_sec);
      }
    }
    else proc_pid_cpu_avail = false;
  }

  // The /proc/<tid>/stat aggregates per-process usage on
  // new Linux kernels 2.6+ where NPTL is supported.
  // The /proc/self/task/<tid>/stat still has the per-thread usage.
  // See bug 6328462.
  // There can be no directory /proc/self/task on kernels 2.4 with NPTL
  // and possibly in some other cases, so we check its availability.
  if (proc_task_unchecked && os::Linux::is_NPTL()) {
    // This is executed only once
    proc_task_unchecked = false;
    fp = fopen("/proc/self/task", "r");
    if (fp != NULL) {
      proc_stat_path = "/proc/self/task/%d/stat";
      fclose(fp);
    }
  }

  sprintf(proc_name, proc_stat_path, tid);
  fp = fopen(proc_name, "r");
  if ( fp == NULL ) return -1;
  statlen = fread(stat, 1, 2047, fp);
  stat[statlen] = '\0';
  fclose(fp);

  // Skip pid and the command string. Note that we could be dealing with
  // weird command names, e.g. user could decide to rename java launcher
  // to "java 1.4.2 :)", then the stat file would look like
  //                1234 (java 1.4.2 :)) R ... ...
  // We don't really need to know the command string, just find the last
  // occurrence of ")" and then start parsing from there. See bug 4726580.
  s = strrchr(stat, ')');
  i = 0;
  if (s == NULL ) return -1;

  // Skip blank chars
  do s++; while (isspace(*s));

  count = sscanf(s,"%c %d %d %d %d %d %lu %lu %lu %lu %lu %lu %lu",
                 &cdummy, &idummy, &idummy, &idummy, &idummy, &idummy,
                 &ldummy, &ldummy, &ldummy, &ldummy, &ldummy,
                 &user_time, &sys_time);
  if ( count != 13 ) return -1;
  if (user_sys_cpu_time) {
    return ((jlong)sys_time + (jlong)user_time) * (1000000000 / clock_tics_per_sec);
  } else {
    return (jlong)user_time * (1000000000 / clock_tics_per_sec);
  }
}

void os::current_thread_cpu_time_info(jvmtiTimerInfo *info_ptr) {
  info_ptr->max_value = ALL_64_BITS;       // will not wrap in less than 64 bits
  info_ptr->may_skip_backward = false;     // elapsed time not wall time
  info_ptr->may_skip_forward = false;      // elapsed time not wall time
  info_ptr->kind = JVMTI_TIMER_TOTAL_CPU;  // user+system time is returned
}

void os::thread_cpu_time_info(jvmtiTimerInfo *info_ptr) {
  info_ptr->max_value = ALL_64_BITS;       // will not wrap in less than 64 bits
  info_ptr->may_skip_backward = false;     // elapsed time not wall time
  info_ptr->may_skip_forward = false;      // elapsed time not wall time
  info_ptr->kind = JVMTI_TIMER_TOTAL_CPU;  // user+system time is returned
}

bool os::is_thread_cpu_time_supported() {
  return true;
}

// System loadavg support.  Returns -1 if load average cannot be obtained.
// Linux doesn't yet have a (official) notion of processor sets,
// so just return the system wide load average.
int os::loadavg(double loadavg[], int nelem) {
  return ::getloadavg(loadavg, nelem);
}

void os::pause() {
  char filename[MAX_PATH];
  if (PauseAtStartupFile && PauseAtStartupFile[0]) {
    jio_snprintf(filename, MAX_PATH, PauseAtStartupFile);
  } else {
    jio_snprintf(filename, MAX_PATH, "./vm.paused.%d", current_process_id());
  }

  int fd = ::open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
  if (fd != -1) {
    struct stat buf;
    ::close(fd);
    while (::stat(filename, &buf) == 0) {
      (void)::poll(NULL, 0, 100);
    }
  } else {
    jio_fprintf(stderr,
      "Could not open pause file '%s', continuing immediately.\n", filename);
  }
}


// Refer to the comments in os_solaris.cpp park-unpark.
//
// Beware -- Some versions of NPTL embody a flaw where pthread_cond_timedwait() can
// hang indefinitely.  For instance NPTL 0.60 on 2.4.21-4ELsmp is vulnerable.
// For specifics regarding the bug see GLIBC BUGID 261237 :
//    http://www.mail-archive.com/debian-glibc@lists.debian.org/msg10837.html.
// Briefly, pthread_cond_timedwait() calls with an expiry time that's not in the future
// will either hang or corrupt the condvar, resulting in subsequent hangs if the condvar
// is used.  (The simple C test-case provided in the GLIBC bug report manifests the
// hang).  The JVM is vulernable via sleep(), Object.wait(timo), LockSupport.parkNanos()
// and monitorenter when we're using 1-0 locking.  All those operations may result in
// calls to pthread_cond_timedwait().  Using LD_ASSUME_KERNEL to use an older version
// of libpthread avoids the problem, but isn't practical.
//
// Possible remedies:
//
// 1.   Establish a minimum relative wait time.  50 to 100 msecs seems to work.
//      This is palliative and probabilistic, however.  If the thread is preempted
//      between the call to compute_abstime() and pthread_cond_timedwait(), more
//      than the minimum period may have passed, and the abstime may be stale (in the
//      past) resultin in a hang.   Using this technique reduces the odds of a hang
//      but the JVM is still vulnerable, particularly on heavily loaded systems.
//
// 2.   Modify park-unpark to use per-thread (per ParkEvent) pipe-pairs instead
//      of the usual flag-condvar-mutex idiom.  The write side of the pipe is set
//      NDELAY. unpark() reduces to write(), park() reduces to read() and park(timo)
//      reduces to poll()+read().  This works well, but consumes 2 FDs per extant
//      thread.
//
// 3.   Embargo pthread_cond_timedwait() and implement a native "chron" thread
//      that manages timeouts.  We'd emulate pthread_cond_timedwait() by enqueuing
//      a timeout request to the chron thread and then blocking via pthread_cond_wait().
//      This also works well.  In fact it avoids kernel-level scalability impediments
//      on certain platforms that don't handle lots of active pthread_cond_timedwait()
//      timers in a graceful fashion.
//
// 4.   When the abstime value is in the past it appears that control returns
//      correctly from pthread_cond_timedwait(), but the condvar is left corrupt.
//      Subsequent timedwait/wait calls may hang indefinitely.  Given that, we
//      can avoid the problem by reinitializing the condvar -- by cond_destroy()
//      followed by cond_init() -- after all calls to pthread_cond_timedwait().
//      It may be possible to avoid reinitialization by checking the return
//      value from pthread_cond_timedwait().  In addition to reinitializing the
//      condvar we must establish the invariant that cond_signal() is only called
//      within critical sections protected by the adjunct mutex.  This prevents
//      cond_signal() from "seeing" a condvar that's in the midst of being
//      reinitialized or that is corrupt.  Sadly, this invariant obviates the
//      desirable signal-after-unlock optimization that avoids futile context switching.
//
//      I'm also concerned that some versions of NTPL might allocate an auxilliary
//      structure when a condvar is used or initialized.  cond_destroy()  would
//      release the helper structure.  Our reinitialize-after-timedwait fix
//      put excessive stress on malloc/free and locks protecting the c-heap.
//
// We currently use (4).  See the WorkAroundNTPLTimedWaitHang flag.
// It may be possible to refine (4) by checking the kernel and NTPL verisons
// and only enabling the work-around for vulnerable environments.

// utility to compute the abstime argument to timedwait:
// millis is the relative timeout time
// abstime will be the absolute timeout time
// TODO: replace compute_abstime() with unpackTime()

static struct timespec* compute_abstime(timespec* abstime, jlong millis) {
  if (millis < 0)  millis = 0;

  jlong seconds = millis / 1000;
  millis %= 1000;
  if (seconds > 50000000) { // see man cond_timedwait(3T)
    seconds = 50000000;
  }

  if (os::Linux::supports_monotonic_clock()) {
    struct timespec now;
    int status = os::Linux::clock_gettime(CLOCK_MONOTONIC, &now);
    assert_status(status == 0, status, "clock_gettime");
    abstime->tv_sec = now.tv_sec  + seconds;
    long nanos = now.tv_nsec + millis * NANOSECS_PER_MILLISEC;
    if (nanos >= NANOSECS_PER_SEC) {
      abstime->tv_sec += 1;
      nanos -= NANOSECS_PER_SEC;
    }
    abstime->tv_nsec = nanos;
  } else {
    struct timeval now;
    int status = gettimeofday(&now, NULL);
    assert(status == 0, "gettimeofday");
    abstime->tv_sec = now.tv_sec  + seconds;
    long usec = now.tv_usec + millis * 1000;
    if (usec >= 1000000) {
      abstime->tv_sec += 1;
      usec -= 1000000;
    }
    abstime->tv_nsec = usec * 1000;
  }
  return abstime;
}


// Test-and-clear _Event, always leaves _Event set to 0, returns immediately.
// Conceptually TryPark() should be equivalent to park(0).

int os::PlatformEvent::TryPark() {
  for (;;) {
    const int v = _Event ;
    guarantee ((v == 0) || (v == 1), "invariant") ;
    if (Atomic::cmpxchg (0, &_Event, v) == v) return v  ;
  }
}

void os::PlatformEvent::park() {       // AKA "down()"
  // Invariant: Only the thread associated with the Event/PlatformEvent
  // may call park().
  // TODO: assert that _Assoc != NULL or _Assoc == Self
  int v ;
  for (;;) {
      v = _Event ;
      if (Atomic::cmpxchg (v-1, &_Event, v) == v) break ;
  }
  guarantee (v >= 0, "invariant") ;
  if (v == 0) {
     // Do this the hard way by blocking ...
     int status = pthread_mutex_lock(_mutex);
     assert_status(status == 0, status, "mutex_lock");
     guarantee (_nParked == 0, "invariant") ;
     ++ _nParked ;
     while (_Event < 0) {
        status = pthread_cond_wait(_cond, _mutex);
        // for some reason, under 2.7 lwp_cond_wait() may return ETIME ...
        // Treat this the same as if the wait was interrupted
        if (status == ETIME) { status = EINTR; }
        assert_status(status == 0 || status == EINTR, status, "cond_wait");
     }
     -- _nParked ;

    _Event = 0 ;
     status = pthread_mutex_unlock(_mutex);
     assert_status(status == 0, status, "mutex_unlock");
    // Paranoia to ensure our locked and lock-free paths interact
    // correctly with each other.
    OrderAccess::fence();
  }
  guarantee (_Event >= 0, "invariant") ;
}

int os::PlatformEvent::park(jlong millis) {
  guarantee (_nParked == 0, "invariant") ;

  int v ;
  for (;;) {
      v = _Event ;
      if (Atomic::cmpxchg (v-1, &_Event, v) == v) break ;
  }
  guarantee (v >= 0, "invariant") ;
  if (v != 0) return OS_OK ;

  // We do this the hard way, by blocking the thread.
  // Consider enforcing a minimum timeout value.
  struct timespec abst;
  compute_abstime(&abst, millis);

  int ret = OS_TIMEOUT;
  int status = pthread_mutex_lock(_mutex);
  assert_status(status == 0, status, "mutex_lock");
  guarantee (_nParked == 0, "invariant") ;
  ++_nParked ;

  // Object.wait(timo) will return because of
  // (a) notification
  // (b) timeout
  // (c) thread.interrupt
  //
  // Thread.interrupt and object.notify{All} both call Event::set.
  // That is, we treat thread.interrupt as a special case of notification.
  // The underlying Solaris implementation, cond_timedwait, admits
  // spurious/premature wakeups, but the JLS/JVM spec prevents the
  // JVM from making those visible to Java code.  As such, we must
  // filter out spurious wakeups.  We assume all ETIME returns are valid.
  //
  // TODO: properly differentiate simultaneous notify+interrupt.
  // In that case, we should propagate the notify to another waiter.

  while (_Event < 0) {
    status = os::Linux::safe_cond_timedwait(_cond, _mutex, &abst);
    if (status != 0 && WorkAroundNPTLTimedWaitHang) {
      pthread_cond_destroy (_cond);
      pthread_cond_init (_cond, os::Linux::condAttr()) ;
    }
    assert_status(status == 0 || status == EINTR ||
                  status == ETIME || status == ETIMEDOUT,
                  status, "cond_timedwait");
    if (!FilterSpuriousWakeups) break ;                 // previous semantics
    if (status == ETIME || status == ETIMEDOUT) break ;
    // We consume and ignore EINTR and spurious wakeups.
  }
  --_nParked ;
  if (_Event >= 0) {
     ret = OS_OK;
  }
  _Event = 0 ;
  status = pthread_mutex_unlock(_mutex);
  assert_status(status == 0, status, "mutex_unlock");
  assert (_nParked == 0, "invariant") ;
  // Paranoia to ensure our locked and lock-free paths interact
  // correctly with each other.
  OrderAccess::fence();
  return ret;
}

void os::PlatformEvent::unpark() {
  // Transitions for _Event:
  //    0 :=> 1
  //    1 :=> 1
  //   -1 :=> either 0 or 1; must signal target thread
  //          That is, we can safely transition _Event from -1 to either
  //          0 or 1. Forcing 1 is slightly more efficient for back-to-back
  //          unpark() calls.
  // See also: "Semaphores in Plan 9" by Mullender & Cox
  //
  // Note: Forcing a transition from "-1" to "1" on an unpark() means
  // that it will take two back-to-back park() calls for the owning
  // thread to block. This has the benefit of forcing a spurious return
  // from the first park() call after an unpark() call which will help
  // shake out uses of park() and unpark() without condition variables.

  if (Atomic::xchg(1, &_Event) >= 0) return;

  // Wait for the thread associated with the event to vacate
  int status = pthread_mutex_lock(_mutex);
  assert_status(status == 0, status, "mutex_lock");
  int AnyWaiters = _nParked;
  assert(AnyWaiters == 0 || AnyWaiters == 1, "invariant");
  if (AnyWaiters != 0 && WorkAroundNPTLTimedWaitHang) {
    AnyWaiters = 0;
    pthread_cond_signal(_cond);
  }
  status = pthread_mutex_unlock(_mutex);
  assert_status(status == 0, status, "mutex_unlock");
  if (AnyWaiters != 0) {
    status = pthread_cond_signal(_cond);
    assert_status(status == 0, status, "cond_signal");
  }

  // Note that we signal() _after dropping the lock for "immortal" Events.
  // This is safe and avoids a common class of  futile wakeups.  In rare
  // circumstances this can cause a thread to return prematurely from
  // cond_{timed}wait() but the spurious wakeup is benign and the victim will
  // simply re-test the condition and re-park itself.
}


// JSR166
// -------------------------------------------------------

/*
 * The solaris and linux implementations of park/unpark are fairly
 * conservative for now, but can be improved. They currently use a
 * mutex/condvar pair, plus a a count.
 * Park decrements count if > 0, else does a condvar wait.  Unpark
 * sets count to 1 and signals condvar.  Only one thread ever waits
 * on the condvar. Contention seen when trying to park implies that someone
 * is unparking you, so don't wait. And spurious returns are fine, so there
 * is no need to track notifications.
 */

/*
 * This code is common to linux and solaris and will be moved to a
 * common place in dolphin.
 *
 * The passed in time value is either a relative time in nanoseconds
 * or an absolute time in milliseconds. Either way it has to be unpacked
 * into suitable seconds and nanoseconds components and stored in the
 * given timespec structure.
 * Given time is a 64-bit value and the time_t used in the timespec is only
 * a signed-32-bit value (except on 64-bit Linux) we have to watch for
 * overflow if times way in the future are given. Further on Solaris versions
 * prior to 10 there is a restriction (see cond_timedwait) that the specified
 * number of seconds, in abstime, is less than current_time  + 100,000,000.
 * As it will be 28 years before "now + 100000000" will overflow we can
 * ignore overflow and just impose a hard-limit on seconds using the value
 * of "now + 100,000,000". This places a limit on the timeout of about 3.17
 * years from "now".
 */

static void unpackTime(timespec* absTime, bool isAbsolute, jlong time) {
  assert (time > 0, "convertTime");
  time_t max_secs = 0;

  if (!os::Linux::supports_monotonic_clock() || isAbsolute) {
    struct timeval now;
    int status = gettimeofday(&now, NULL);
    assert(status == 0, "gettimeofday");

    max_secs = now.tv_sec + MAX_SECS;

    if (isAbsolute) {
      jlong secs = time / 1000;
      if (secs > max_secs) {
        absTime->tv_sec = max_secs;
      } else {
        absTime->tv_sec = secs;
      }
      absTime->tv_nsec = (time % 1000) * NANOSECS_PER_MILLISEC;
    } else {
      jlong secs = time / NANOSECS_PER_SEC;
      if (secs >= MAX_SECS) {
        absTime->tv_sec = max_secs;
        absTime->tv_nsec = 0;
      } else {
        absTime->tv_sec = now.tv_sec + secs;
        absTime->tv_nsec = (time % NANOSECS_PER_SEC) + now.tv_usec*1000;
        if (absTime->tv_nsec >= NANOSECS_PER_SEC) {
          absTime->tv_nsec -= NANOSECS_PER_SEC;
          ++absTime->tv_sec; // note: this must be <= max_secs
        }
      }
    }
  } else {
    // must be relative using monotonic clock
    struct timespec now;
    int status = os::Linux::clock_gettime(CLOCK_MONOTONIC, &now);
    assert_status(status == 0, status, "clock_gettime");
    max_secs = now.tv_sec + MAX_SECS;
    jlong secs = time / NANOSECS_PER_SEC;
    if (secs >= MAX_SECS) {
      absTime->tv_sec = max_secs;
      absTime->tv_nsec = 0;
    } else {
      absTime->tv_sec = now.tv_sec + secs;
      absTime->tv_nsec = (time % NANOSECS_PER_SEC) + now.tv_nsec;
      if (absTime->tv_nsec >= NANOSECS_PER_SEC) {
        absTime->tv_nsec -= NANOSECS_PER_SEC;
        ++absTime->tv_sec; // note: this must be <= max_secs
      }
    }
  }
  assert(absTime->tv_sec >= 0, "tv_sec < 0");
  assert(absTime->tv_sec <= max_secs, "tv_sec > max_secs");
  assert(absTime->tv_nsec >= 0, "tv_nsec < 0");
  assert(absTime->tv_nsec < NANOSECS_PER_SEC, "tv_nsec >= nanos_per_sec");
}

void Parker::park(bool isAbsolute, jlong time) {
  // Ideally we'd do something useful while spinning, such
  // as calling unpackTime().

  // Optional fast-path check:
  // Return immediately if a permit is available.
  // We depend on Atomic::xchg() having full barrier semantics
  // since we are doing a lock-free update to _counter.
  if (Atomic::xchg(0, &_counter) > 0) return;

  Thread* thread = Thread::current();
  assert(thread->is_Java_thread(), "Must be JavaThread");
  JavaThread *jt = (JavaThread *)thread;

  // Optional optimization -- avoid state transitions if there's an interrupt pending.
  // Check interrupt before trying to wait
  if (Thread::is_interrupted(thread, false)) {
    return;
  }

  // Next, demultiplex/decode time arguments
  timespec absTime;
  if (time < 0 || (isAbsolute && time == 0) ) { // don't wait at all
    return;
  }
  if (time > 0) {
    unpackTime(&absTime, isAbsolute, time);
  }


  // Enter safepoint region
  // Beware of deadlocks such as 6317397.
  // The per-thread Parker:: mutex is a classic leaf-lock.
  // In particular a thread must never block on the Threads_lock while
  // holding the Parker:: mutex.  If safepoints are pending both the
  // the ThreadBlockInVM() CTOR and DTOR may grab Threads_lock.
  ThreadBlockInVM tbivm(jt);

  // Don't wait if cannot get lock since interference arises from
  // unblocking.  Also. check interrupt before trying wait
  if (Thread::is_interrupted(thread, false) || pthread_mutex_trylock(_mutex) != 0) {
    return;
  }

  int status ;
  if (_counter > 0)  { // no wait needed
    _counter = 0;
    status = pthread_mutex_unlock(_mutex);
    assert (status == 0, "invariant") ;
    // Paranoia to ensure our locked and lock-free paths interact
    // correctly with each other and Java-level accesses.
    OrderAccess::fence();
    return;
  }

#ifdef ASSERT
  // Don't catch signals while blocked; let the running threads have the signals.
  // (This allows a debugger to break into the running thread.)
  sigset_t oldsigs;
  sigset_t* allowdebug_blocked = os::Linux::allowdebug_blocked_signals();
  pthread_sigmask(SIG_BLOCK, allowdebug_blocked, &oldsigs);
#endif

  OSThreadWaitState osts(thread->osthread(), false /* not Object.wait() */);
  jt->set_suspend_equivalent();
  // cleared by handle_special_suspend_equivalent_condition() or java_suspend_self()
  assert(_cur_index == -1, "invariant");
  if (time == 0) {
    _cur_index = REL_INDEX; // arbitrary choice when not timed
    status = pthread_cond_wait (&_cond[_cur_index], _mutex) ;
  } else {
    _cur_index = isAbsolute ? ABS_INDEX : REL_INDEX;
    status = os::Linux::safe_cond_timedwait (&_cond[_cur_index], _mutex, &absTime) ;
    if (status != 0 && WorkAroundNPTLTimedWaitHang) {
      pthread_cond_destroy (&_cond[_cur_index]) ;
      pthread_cond_init    (&_cond[_cur_index], isAbsolute ? NULL : os::Linux::condAttr());
    }
  }
  _cur_index = -1;

  assert_status(status == 0 || status == EINTR ||
                status == ETIME || status == ETIMEDOUT,
                status, "cond_timedwait");

#ifdef ASSERT
  pthread_sigmask(SIG_SETMASK, &oldsigs, NULL);
#endif

  _counter = 0 ;
  status = pthread_mutex_unlock(_mutex) ;
  assert_status(status == 0, status, "invariant") ;
  // Paranoia to ensure our locked and lock-free paths interact
  // correctly with each other and Java-level accesses.
  OrderAccess::fence();

  // If externally suspended while waiting, re-suspend
  if (jt->handle_special_suspend_equivalent_condition()) {
    jt->java_suspend_self();
  }
}

void Parker::unpark() {
  int s, status ;
  status = pthread_mutex_lock(_mutex);
  assert (status == 0, "invariant") ;
  s = _counter;
  _counter = 1;
  if (s < 1) {
    // thread might be parked
    if (_cur_index != -1) {
      // thread is definitely parked
      if (WorkAroundNPTLTimedWaitHang) {
        status = pthread_cond_signal (&_cond[_cur_index]);
        assert (status == 0, "invariant");
        status = pthread_mutex_unlock(_mutex);
        assert (status == 0, "invariant");
      } else {
        status = pthread_mutex_unlock(_mutex);
        assert (status == 0, "invariant");
        status = pthread_cond_signal (&_cond[_cur_index]);
        assert (status == 0, "invariant");
      }
    } else {
      pthread_mutex_unlock(_mutex);
      assert (status == 0, "invariant") ;
    }
  } else {
    pthread_mutex_unlock(_mutex);
    assert (status == 0, "invariant") ;
  }
}


extern char** environ;

#ifndef __NR_fork
#define __NR_fork IA32_ONLY(2) IA64_ONLY(not defined) AMD64_ONLY(57)
#endif

#ifndef __NR_execve
#define __NR_execve IA32_ONLY(11) IA64_ONLY(1033) AMD64_ONLY(59)
#endif

#if defined(SPARC)
// This assembly code makes the call to "syscall(__NR_fork)" and then
// gets the values for "pid" and "is_child" from the correct registers.
// This was done to make sure the compiler does not change the order
// of the instructions while optimizing.
void sparc_fork(int nr_fork, pid_t *pid, int *ischild) {
  asm volatile (
    " mov %2, %%o0\n\t"
    " call syscall, 0\n\t"
    " nop\n\t"
    " mov %%o0, %0\n\t"
    " mov %%o1, %1\n\t"
    : "=r" (*pid), "=r" (*ischild)
    : "r" (nr_fork) :
  );
}
#endif

// Run the specified command in a separate process. Return its exit value,
// or -1 on failure (e.g. can't fork a new process).
// Unlike system(), this function can be called from signal handler. It
// doesn't block SIGINT et al.
int os::fork_and_exec(char* cmd) {
  const char * argv[4] = {"sh", "-c", cmd, NULL};
  int is_child;
  pid_t pid;

  // fork() in LinuxThreads/NPTL is not async-safe. It needs to run
  // pthread_atfork handlers and reset pthread library. All we need is a
  // separate process to execve. Make a direct syscall to fork process.
  // On IA64 there's no fork syscall, we have to use fork() and hope for
  // the best...
#if defined(SPARC)
  sparc_fork(__NR_fork, &pid, &is_child);
#else
  pid = NOT_IA64(syscall(__NR_fork);)
              IA64_ONLY(fork();)

  // set the is_child flag by checking the pid
  if (pid == 0) {
    is_child = 1;
  } else {
    is_child = 0;
  }
#endif

  if (pid < 0) {
    // fork failed
    return -1;

  } else if (is_child) {
    // child process

    // execve() in LinuxThreads will call pthread_kill_other_threads_np()
    // first to kill every thread on the thread list. Because this list is
    // not reset by fork() (see notes above), execve() will instead kill
    // every thread in the parent process. We know this is the only thread
    // in the new process, so make a system call directly.
    // IA64 should use normal execve() from glibc to match the glibc fork()
    // above.
    NOT_IA64(syscall(__NR_execve, "/bin/sh", argv, environ);)
    IA64_ONLY(execve("/bin/sh", (char* const*)argv, environ);)

    // execve failed
    _exit(-1);

  } else  {
    // copied from J2SE ..._waitForProcessExit() in UNIXProcess_md.c; we don't
    // care about the actual exit code, for now.

    int status;

    // Wait for the child process to exit.  This returns immediately if
    // the child has already exited. */
    while (waitpid(pid, &status, 0) < 0) {
        switch (errno) {
        case ECHILD: return 0;
        case EINTR: break;
        default: return -1;
        }
    }

    if (WIFEXITED(status)) {
       // The child exited normally; get its exit code.
       return WEXITSTATUS(status);
    } else if (WIFSIGNALED(status)) {
       // The child exited because of a signal
       // The best value to return is 0x80 + signal number,
       // because that is what all Unix shells do, and because
       // it allows callers to distinguish between process exit and
       // process death by signal.
       return 0x80 + WTERMSIG(status);
    } else {
       // Unknown exit code; pass it through
       return status;
    }
  }
}

// is_headless_jre()
//
// Test for the existence of xawt/libmawt.so or libawt_xawt.so
// in order to report if we are running in a headless jre
//
// Since JDK8 xawt/libmawt.so was moved into the same directory
// as libawt.so, and renamed libawt_xawt.so
//
bool os::is_headless_jre() {
    struct stat statbuf;
    char buf[MAXPATHLEN];
    char libmawtpath[MAXPATHLEN];
    const char *xawtstr  = "/xawt/libmawt.so";
    const char *new_xawtstr = "/libawt_xawt.so";
    char *p;

    // Get path to libjvm.so
    os::jvm_path(buf, sizeof(buf));

    // Get rid of libjvm.so
    p = strrchr(buf, '/');
    if (p == NULL) return false;
    else *p = '\0';

    // Get rid of client or server
    p = strrchr(buf, '/');
    if (p == NULL) return false;
    else *p = '\0';

    // check xawt/libmawt.so
    strcpy(libmawtpath, buf);
    strcat(libmawtpath, xawtstr);
    if (::stat(libmawtpath, &statbuf) == 0) return false;

    // check libawt_xawt.so
    strcpy(libmawtpath, buf);
    strcat(libmawtpath, new_xawtstr);
    if (::stat(libmawtpath, &statbuf) == 0) return false;

    return true;
}

// Get the default path to the core file
// Returns the length of the string
int os::get_core_path(char* buffer, size_t bufferSize) {
  const char* p = get_current_directory(buffer, bufferSize);

  if (p == NULL) {
    assert(p != NULL, "failed to get current directory");
    return 0;
  }

  return strlen(buffer);
}

#ifdef JAVASE_EMBEDDED
//
// A thread to watch the '/dev/mem_notify' device, which will tell us when the OS is running low on memory.
//
MemNotifyThread* MemNotifyThread::_memnotify_thread = NULL;

// ctor
//
MemNotifyThread::MemNotifyThread(int fd): Thread() {
  assert(memnotify_thread() == NULL, "we can only allocate one MemNotifyThread");
  _fd = fd;

  if (os::create_thread(this, os::os_thread)) {
    _memnotify_thread = this;
    os::set_priority(this, NearMaxPriority);
    os::start_thread(this);
  }
}

// Where all the work gets done
//
void MemNotifyThread::run() {
  assert(this == memnotify_thread(), "expected the singleton MemNotifyThread");

  // Set up the select arguments
  fd_set rfds;
  if (_fd != -1) {
    FD_ZERO(&rfds);
    FD_SET(_fd, &rfds);
  }

  // Now wait for the mem_notify device to wake up
  while (1) {
    // Wait for the mem_notify device to signal us..
    int rc = select(_fd+1, _fd != -1 ? &rfds : NULL, NULL, NULL, NULL);
    if (rc == -1) {
      perror("select!\n");
      break;
    } else if (rc) {
      //ssize_t free_before = os::available_memory();
      //tty->print ("Notified: Free: %dK \n",os::available_memory()/1024);

      // The kernel is telling us there is not much memory left...
      // try to do something about that

      // If we are not already in a GC, try one.
      if (!Universe::heap()->is_gc_active()) {
        Universe::heap()->collect(GCCause::_allocation_failure);

        //ssize_t free_after = os::available_memory();
        //tty->print ("Post-Notify: Free: %dK\n",free_after/1024);
        //tty->print ("GC freed: %dK\n", (free_after - free_before)/1024);
      }
      // We might want to do something like the following if we find the GC's are not helping...
      // Universe::heap()->size_policy()->set_gc_time_limit_exceeded(true);
    }
  }
}

//
// See if the /dev/mem_notify device exists, and if so, start a thread to monitor it.
//
void MemNotifyThread::start() {
  int    fd;
  fd = open ("/dev/mem_notify", O_RDONLY, 0);
  if (fd < 0) {
      return;
  }

  if (memnotify_thread() == NULL) {
    new MemNotifyThread(fd);
  }
}

#endif // JAVASE_EMBEDDED


/////////////// Unit tests ///////////////

#ifndef PRODUCT

#define test_log(...) \
  do {\
    if (VerboseInternalVMTests) { \
      tty->print_cr(__VA_ARGS__); \
      tty->flush(); \
    }\
  } while (false)

class TestReserveMemorySpecial : AllStatic {
 public:
  static void small_page_write(void* addr, size_t size) {
    size_t page_size = os::vm_page_size();

    char* end = (char*)addr + size;
    for (char* p = (char*)addr; p < end; p += page_size) {
      *p = 1;
    }
  }

  static void test_reserve_memory_special_huge_tlbfs_only(size_t size) {
    if (!UseHugeTLBFS) {
      return;
    }

    test_log("test_reserve_memory_special_huge_tlbfs_only(" SIZE_FORMAT ")", size);

    char* addr = os::Linux::reserve_memory_special_huge_tlbfs_only(size, NULL, false);

    if (addr != NULL) {
      small_page_write(addr, size);

      os::Linux::release_memory_special_huge_tlbfs(addr, size);
    }
  }

  static void test_reserve_memory_special_huge_tlbfs_only() {
    if (!UseHugeTLBFS) {
      return;
    }

    size_t lp = os::large_page_size();

    for (size_t size = lp; size <= lp * 10; size += lp) {
      test_reserve_memory_special_huge_tlbfs_only(size);
    }
  }

  static void test_reserve_memory_special_huge_tlbfs_mixed(size_t size, size_t alignment) {
    if (!UseHugeTLBFS) {
        return;
    }

    test_log("test_reserve_memory_special_huge_tlbfs_mixed(" SIZE_FORMAT ", " SIZE_FORMAT ")",
        size, alignment);

    assert(size >= os::large_page_size(), "Incorrect input to test");

    char* addr = os::Linux::reserve_memory_special_huge_tlbfs_mixed(size, alignment, NULL, false);

    if (addr != NULL) {
      small_page_write(addr, size);

      os::Linux::release_memory_special_huge_tlbfs(addr, size);
    }
  }

  static void test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(size_t size) {
    size_t lp = os::large_page_size();
    size_t ag = os::vm_allocation_granularity();

    for (size_t alignment = ag; is_size_aligned(size, alignment); alignment *= 2) {
      test_reserve_memory_special_huge_tlbfs_mixed(size, alignment);
    }
  }

  static void test_reserve_memory_special_huge_tlbfs_mixed() {
    size_t lp = os::large_page_size();
    size_t ag = os::vm_allocation_granularity();

    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp + ag);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp + lp / 2);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 2);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 2 + ag);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 2 - ag);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 2 + lp / 2);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 10);
    test_reserve_memory_special_huge_tlbfs_mixed_all_alignments(lp * 10 + lp / 2);
  }

  static void test_reserve_memory_special_huge_tlbfs() {
    if (!UseHugeTLBFS) {
      return;
    }

    test_reserve_memory_special_huge_tlbfs_only();
    test_reserve_memory_special_huge_tlbfs_mixed();
  }

  static void test_reserve_memory_special_shm(size_t size, size_t alignment) {
    if (!UseSHM) {
      return;
    }

    test_log("test_reserve_memory_special_shm(" SIZE_FORMAT ", " SIZE_FORMAT ")", size, alignment);

    char* addr = os::Linux::reserve_memory_special_shm(size, alignment, NULL, false);

    if (addr != NULL) {
      assert(is_ptr_aligned(addr, alignment), "Check");
      assert(is_ptr_aligned(addr, os::large_page_size()), "Check");

      small_page_write(addr, size);

      os::Linux::release_memory_special_shm(addr, size);
    }
  }

  static void test_reserve_memory_special_shm() {
    size_t lp = os::large_page_size();
    size_t ag = os::vm_allocation_granularity();

    for (size_t size = ag; size < lp * 3; size += ag) {
      for (size_t alignment = ag; is_size_aligned(size, alignment); alignment *= 2) {
        test_reserve_memory_special_shm(size, alignment);
      }
    }
  }

  static void test() {
    test_reserve_memory_special_huge_tlbfs();
    test_reserve_memory_special_shm();
  }
};

void TestReserveMemorySpecial_test() {
  TestReserveMemorySpecial::test();
}

#endif