Quelle os_linux.cpp Sprache: C

/*
* Copyright (c) 1999, 2022, Oracle and/or its affiliates. All rights reserved.
* Copyright (c) 2015, 2022 SAP SE. 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/vmSymbols.hpp"
#include "code/icBuffer.hpp"
#include "code/vtableStubs.hpp"
#include "compiler/compileBroker.hpp"
#include "compiler/disassembler.hpp"
#include "interpreter/interpreter.hpp"
#include "jvm.h"
#include "jvmtifiles/jvmti.h"
#include "logging/log.hpp"
#include "logging/logStream.hpp"
#include "memory/allocation.inline.hpp"
#include "oops/oop.inline.hpp"
#include "os_linux.inline.hpp"
#include "os_posix.inline.hpp"
#include "osContainer_linux.hpp"
#include "prims/jniFastGetField.hpp"
#include "prims/jvm_misc.hpp"
#include "runtime/arguments.hpp"
#include "runtime/atomic.hpp"
#include "runtime/globals.hpp"
#include "runtime/globals_extension.hpp"
#include "runtime/init.hpp"
#include "runtime/interfaceSupport.inline.hpp"
#include "runtime/java.hpp"
#include "runtime/javaCalls.hpp"
#include "runtime/javaThread.hpp"
#include "runtime/mutexLocker.hpp"
#include "runtime/objectMonitor.hpp"
#include "runtime/osInfo.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/threads.hpp"
#include "runtime/threadSMR.hpp"
#include "runtime/timer.hpp"
#include "runtime/vm_version.hpp"
#include "signals_posix.hpp"
#include "semaphore_posix.hpp"
#include "services/memTracker.hpp"
#include "services/runtimeService.hpp"
#include "utilities/align.hpp"
#include "utilities/decoder.hpp"
#include "utilities/defaultStream.hpp"
#include "utilities/events.hpp"
#include "utilities/elfFile.hpp"
#include "utilities/growableArray.hpp"
#include "utilities/globalDefinitions.hpp"
#include "utilities/macros.hpp"
#include "utilities/powerOfTwo.hpp"
#include "utilities/vmError.hpp"

// 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 <endian.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 <pwd.h>
# include <poll.h>
# include <fcntl.h>
# include <string.h>
# include <syscall.h>
# include <sys/sysinfo.h>
# include <sys/ipc.h>
# include <sys/shm.h>
# include <link.h>
# include <stdint.h>
# include <inttypes.h>
# include <sys/ioctl.h>
# include <linux/elf-em.h>
#ifdef __GLIBC__
# include <malloc.h>
#endif

#ifndef _GNU_SOURCE
  #define _GNU_SOURCE
  #include <sched.h>
  #undef _GNU_SOURCE
#else
  #include <sched.h>
#endif

// 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)

#ifdef MUSL_LIBC
// dlvsym is not a part of POSIX
// and musl libc doesn't implement it.
static void *dlvsym(void *handle,
                    const char *symbol,
                    const char *version) {
   // load the latest version of symbol
   return dlsym(handle, symbol);
}
#endif

enum CoredumpFilterBit {
  FILE_BACKED_PVT_BIT = 1 << 2,
  FILE_BACKED_SHARED_BIT = 1 << 3,
  LARGEPAGES_BIT = 1 << 6,
  DAX_SHARED_BIT = 1 << 8
};

////////////////////////////////////////////////////////////////////////////////
// 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::_pthread_getcpuclockid)(pthread_t, clockid_t *) = NULL;
int (*os::Linux::_pthread_setname_np)(pthread_t, const char*) = NULL;
pthread_t os::Linux::_main_thread;
bool os::Linux::_supports_fast_thread_cpu_time = false;
const char * os::Linux::_libc_version = NULL;
const char * os::Linux::_libpthread_version = NULL;
size_t os::Linux::_default_large_page_size = 0;

#ifdef __GLIBC__
// We want to be buildable and runnable on older and newer glibcs, so resolve both
// mallinfo and mallinfo2 dynamically.
struct old_mallinfo {
  int arena;
  int ordblks;
  int smblks;
  int hblks;
  int hblkhd;
  int usmblks;
  int fsmblks;
  int uordblks;
  int fordblks;
  int keepcost;
};
typedef struct old_mallinfo (*mallinfo_func_t)(void);
static mallinfo_func_t g_mallinfo = NULL;

struct new_mallinfo {
  size_t arena;
  size_t ordblks;
  size_t smblks;
  size_t hblks;
  size_t hblkhd;
  size_t usmblks;
  size_t fsmblks;
  size_t uordblks;
  size_t fordblks;
  size_t keepcost;
};
typedef struct new_mallinfo (*mallinfo2_func_t)(void);
static mallinfo2_func_t g_mallinfo2 = NULL;
#endif // __GLIBC__

static int clock_tics_per_sec = 100;

// If the VM might have been created on the primordial thread, we need to resolve the
// primordial thread stack bounds and check if the current thread might be the
// primordial thread in places. If we know that the primordial thread is never used,
// such as when the VM was created by one of the standard java launchers, we can
// avoid this
static bool suppress_primordial_thread_resolution = false;

// utility functions

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

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

  if (OSContainer::is_containerized()) {
    jlong mem_limit = OSContainer::memory_limit_in_bytes();
    jlong mem_usage;
    if (mem_limit > 0 && (mem_usage = OSContainer::memory_usage_in_bytes()) < 1) {
      log_debug(os, container)("container memory usage failed: " JLONG_FORMAT ", using host value", mem_usage);
    }
    if (mem_limit > 0 && mem_usage > 0) {
      avail_mem = mem_limit > mem_usage ? (julong)mem_limit - (julong)mem_usage : 0;
      log_trace(os)("available container memory: " JULONG_FORMAT, avail_mem);
      return avail_mem;
    }
  }

  sysinfo(&si);
  avail_mem = (julong)si.freeram * si.mem_unit;
  log_trace(os)("available memory: " JULONG_FORMAT, avail_mem);
  return avail_mem;
}

julong os::physical_memory() {
  jlong phys_mem = 0;
  if (OSContainer::is_containerized()) {
    jlong mem_limit;
    if ((mem_limit = OSContainer::memory_limit_in_bytes()) > 0) {
      log_trace(os)("total container memory: " JLONG_FORMAT, mem_limit);
      return mem_limit;
    }
  }

  phys_mem = Linux::physical_memory();
  log_trace(os)("total system memory: " JLONG_FORMAT, phys_mem);
  return phys_mem;
}

static uint64_t initial_total_ticks = 0;
static uint64_t initial_steal_ticks = 0;
static bool     has_initial_tick_info = false;

static void next_line(FILE *f) {
  int c;
  do {
    c = fgetc(f);
  } while (c != '\n' && c != EOF);
}

bool os::Linux::get_tick_information(CPUPerfTicks* pticks, int which_logical_cpu) {
  FILE*         fh;
  uint64_t      userTicks, niceTicks, systemTicks, idleTicks;
  // since at least kernel 2.6 : iowait: time waiting for I/O to complete
  // irq: time  servicing interrupts; softirq: time servicing softirqs
  uint64_t      iowTicks = 0, irqTicks = 0, sirqTicks= 0;
  // steal (since kernel 2.6.11): time spent in other OS when running in a virtualized environment
  uint64_t      stealTicks = 0;
  // guest (since kernel 2.6.24): time spent running a virtual CPU for guest OS under the
  // control of the Linux kernel
  uint64_t      guestNiceTicks = 0;
  int           logical_cpu = -1;
  const int     required_tickinfo_count = (which_logical_cpu == -1) ? 4 : 5;
  int           n;

  memset(pticks, 0, sizeof(CPUPerfTicks));

  if ((fh = os::fopen("/proc/stat", "r")) == NULL) {
    return false;
  }

  if (which_logical_cpu == -1) {
    n = fscanf(fh, "cpu " UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " "
            UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " "
            UINT64_FORMAT " " UINT64_FORMAT " ",
            &userTicks, &niceTicks, &systemTicks, &idleTicks,
            &iowTicks, &irqTicks, &sirqTicks,
            &stealTicks, &guestNiceTicks);
  } else {
    // Move to next line
    next_line(fh);

    // find the line for requested cpu faster to just iterate linefeeds?
    for (int i = 0; i < which_logical_cpu; i++) {
      next_line(fh);
    }

    n = fscanf(fh, "cpu%u " UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " "
               UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " " UINT64_FORMAT " "
               UINT64_FORMAT " " UINT64_FORMAT " ",
               &logical_cpu, &userTicks, &niceTicks,
               &systemTicks, &idleTicks, &iowTicks, &irqTicks, &sirqTicks,
               &stealTicks, &guestNiceTicks);
  }

  fclose(fh);
  if (n < required_tickinfo_count || logical_cpu != which_logical_cpu) {
    return false;
  }
  pticks->used       = userTicks + niceTicks;
  pticks->usedKernel = systemTicks + irqTicks + sirqTicks;
  pticks->total      = userTicks + niceTicks + systemTicks + idleTicks +
                       iowTicks + irqTicks + sirqTicks + stealTicks + guestNiceTicks;

  if (n > required_tickinfo_count + 3) {
    pticks->steal = stealTicks;
    pticks->has_steal_ticks = true;
  } else {
    pticks->steal = 0;
    pticks->has_steal_ticks = false;
  }

  return true;
}

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

// pid_t gettid()
//
// Returns the kernel thread id of the currently running thread. Kernel
// thread id is used to access /proc.
pid_t os::Linux::gettid() {
  int rslt = syscall(SYS_gettid);
  assert(rslt != -1, "must be."); // old linuxthreads implementation?
  return (pid_t)rslt;
}

// Returns the amount of swap currently configured, in bytes.
// This can change at any time.
julong os::Linux::host_swap() {
  struct sysinfo si;
  sysinfo(&si);
  return (julong)si.totalswap;
}

// 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.
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 = os::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() {
  // The next steps are taken in the product version:
  //
  // Obtain the JAVA_HOME value from the location of libjvm.so.
  // This library should be located at:
  // <JAVA_HOME>/lib/{client|server}/libjvm.so.
  //
  // If "/jre/lib/" appears at the right place in the path, then we
  // assume libjvm.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.so" to this path so
  // it looks like libjvm.so is installed there
  // <JAVA_HOME>/jre/lib/<arch>/hotspot/libjvm.so.
  //
  // Otherwise exit.
  //
  // Important note: if the location of libjvm.so changes this
  // code needs to be changed accordingly.

  // 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.
#ifndef OVERRIDE_LIBPATH
  #if defined(_LP64)
    #define DEFAULT_LIBPATH "/usr/lib64:/lib64:/lib:/usr/lib"
  #else
    #define DEFAULT_LIBPATH "/lib:/usr/lib"
  #endif
#else
  #define DEFAULT_LIBPATH OVERRIDE_LIBPATH
#endif

// Base path of extensions installed on the system.
#define SYS_EXT_DIR     "/usr/java/packages"
#define EXTENSIONS_DIR  "/lib/ext"

  // Buffer that fits several sprintfs.
  // Note that the space for the colon and the trailing null are provided
  // by the nulls included by the sizeof operator.
  const size_t bufsize =
    MAX2((size_t)MAXPATHLEN,  // For dll_dir & friends.
         (size_t)MAXPATHLEN + sizeof(EXTENSIONS_DIR) + sizeof(SYS_EXT_DIR) + sizeof(EXTENSIONS_DIR)); // extensions dir
  char *buf = NEW_C_HEAP_ARRAY(char, bufsize, mtInternal);

  // sysclasspath, java_home, dll_dir
  {
    char *pslash;
    os::jvm_path(buf, bufsize);

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

    if (pslash != NULL) {
      pslash = strrchr(buf, '/');
      if (pslash != NULL) {
        *pslash = '\0';        // Get rid of /lib.
      }
    }
    Arguments::set_java_home(buf);
    if (!set_boot_path('/', ':')) {
      vm_exit_during_initialization("Failed setting boot class path.", NULL);
    }
  }

  // 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 accommodate 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.
  {
    // Get the user setting of LD_LIBRARY_PATH, and prepended it. It
    // should always exist (until the legacy problem cited above is
    // addressed).
    const char *v = ::getenv("LD_LIBRARY_PATH");
    const char *v_colon = ":";
    if (v == NULL) { v = ""; v_colon = ""; }
    // That's +1 for the colon and +1 for the trailing '\0'.
    char *ld_library_path = NEW_C_HEAP_ARRAY(char,
                                             strlen(v) + 1 +
                                             sizeof(SYS_EXT_DIR) + sizeof("/lib/") + sizeof(DEFAULT_LIBPATH) + 1,
                                             mtInternal);
    sprintf(ld_library_path, "%s%s" SYS_EXT_DIR "/lib:" DEFAULT_LIBPATH, v, v_colon);
    Arguments::set_library_path(ld_library_path);
    FREE_C_HEAP_ARRAY(char, ld_library_path);
  }

  // Extensions directories.
  sprintf(buf, "%s" EXTENSIONS_DIR ":" SYS_EXT_DIR EXTENSIONS_DIR, Arguments::get_java_home());
  Arguments::set_ext_dirs(buf);

  FREE_C_HEAP_ARRAY(char, buf);

#undef DEFAULT_LIBPATH
#undef SYS_EXT_DIR
#undef EXTENSIONS_DIR
}

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

void os::breakpoint() {
  BREAKPOINT;
}

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

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

void os::Linux::libpthread_init() {
  // Save glibc and pthread version strings.
#if !defined(_CS_GNU_LIBC_VERSION) || \
    !defined(_CS_GNU_LIBPTHREAD_VERSION)
  #error "glibc too old (< 2.3.2)"
#endif

#ifdef MUSL_LIBC
  // confstr() from musl libc returns EINVAL for
  // _CS_GNU_LIBC_VERSION and _CS_GNU_LIBPTHREAD_VERSION
  os::Linux::set_libc_version("musl - unknown");
  os::Linux::set_libpthread_version("musl - unknown");
#else
  size_t n = confstr(_CS_GNU_LIBC_VERSION, NULL, 0);
  assert(n > 0, "cannot retrieve glibc version");
  char *str = (char *)malloc(n, mtInternal);
  confstr(_CS_GNU_LIBC_VERSION, str, n);
  os::Linux::set_libc_version(str);

  n = confstr(_CS_GNU_LIBPTHREAD_VERSION, NULL, 0);
  assert(n > 0, "cannot retrieve pthread version");
  str = (char *)malloc(n, mtInternal);
  confstr(_CS_GNU_LIBPTHREAD_VERSION, str, n);
  os::Linux::set_libpthread_version(str);
#endif
}

/////////////////////////////////////////////////////////////////////////////
// thread stack expansion

// os::Linux::manually_expand_stack() takes care of expanding the thread
// stack. Note that this is normally not needed: pthread stacks allocate
// thread stack using mmap() without MAP_NORESERVE, so the stack is already
// committed. Therefore it is not necessary to expand the stack manually.
//
// Manually expanding the stack was historically needed on LinuxThreads
// thread stacks, which were allocated with mmap(MAP_GROWSDOWN). Nowadays
// it is kept to deal with very rare corner cases:
//
// For one, user may run the VM on an own implementation of threads
// whose stacks are - like the old LinuxThreads - implemented using
// mmap(MAP_GROWSDOWN).
//
// Also, this coding may be needed if the VM is running on the primordial
// thread. Normally we avoid running on the primordial thread; however,
// user may still invoke the VM on the primordial thread.
//
// The following historical comment describes the details about running
// on a thread stack allocated with mmap(MAP_GROWSDOWN):

// 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 MAP_GROWSDOWN.
//
// 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.

static void NOINLINE _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_down((uintptr_t)bottom, os::vm_page_size());
  bottom += os::vm_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';
  }
}

void os::Linux::expand_stack_to(address bottom) {
  _expand_stack_to(bottom);
}

bool os::Linux::manually_expand_stack(JavaThread * t, address addr) {
  assert(t!=NULL, "just checking");
  assert(t->osthread()->expanding_stack(), "expand should be set");

  if (t->is_in_usable_stack(addr)) {
    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

// Thread start routine for all newly created threads
static void *thread_native_entry(Thread *thread) {

  thread->record_stack_base_and_size();

#ifndef __GLIBC__
  // 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.
  // This code is not needed anymore in glibc because it has MULTI_PAGE_ALIASING
  // and we did not see any degradation in performance without `alloca()`.
  static int counter = 0;
  int pid = os::current_process_id();
  int random = ((pid ^ counter++) & 7) * 128;
  void *stackmem = alloca(random != 0 ? random : 1); // ensure we allocate > 0
  // Ensure the alloca result is used in a way that prevents the compiler from eliding it.
  *(char *)stackmem = 1;
#endif

  thread->initialize_thread_current();

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

  osthread->set_thread_id(os::current_thread_id());

  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
  PosixSignals::hotspot_sigmask(thread);

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

  // handshaking with parent thread
  {
    MutexLocker 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_without_safepoint_check();
    }
  }

  log_info(os, thread)("Thread is alive (tid: " UINTX_FORMAT ", pthread id: " UINTX_FORMAT ").",
    os::current_thread_id(), (uintx) pthread_self());

  assert(osthread->pthread_id() != 0, "pthread_id was not set as expected");

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

  // Note: at this point the thread object may already have deleted itself.
  // Prevent dereferencing it from here on out.
  thread = NULL;

  log_info(os, thread)("Thread finished (tid: " UINTX_FORMAT ", pthread id: " UINTX_FORMAT ").",
    os::current_thread_id(), (uintx) pthread_self());

  return 0;
}

// On Linux, glibc places static TLS blocks (for __thread variables) on
// the thread stack. This decreases the stack size actually available
// to threads.
//
// For large static TLS sizes, this may cause threads to malfunction due
// to insufficient stack space. This is a well-known issue in glibc:
// http://sourceware.org/bugzilla/show_bug.cgi?id=11787.
//
// As a workaround, we call a private but assumed-stable glibc function,
// __pthread_get_minstack() to obtain the minstack size and derive the
// static TLS size from it. We then increase the user requested stack
// size by this TLS size.
//
// Due to compatibility concerns, this size adjustment is opt-in and
// controlled via AdjustStackSizeForTLS.
typedef size_t (*GetMinStack)(const pthread_attr_t *attr);

GetMinStack _get_minstack_func = NULL;

static void get_minstack_init() {
  _get_minstack_func =
        (GetMinStack)dlsym(RTLD_DEFAULT, "__pthread_get_minstack");
  log_info(os, thread)("Lookup of __pthread_get_minstack %s",
                       _get_minstack_func == NULL ? "failed" : "succeeded");
}

// Returns the size of the static TLS area glibc puts on thread stacks.
// The value is cached on first use, which occurs when the first thread
// is created during VM initialization.
static size_t get_static_tls_area_size(const pthread_attr_t *attr) {
  size_t tls_size = 0;
  if (_get_minstack_func != NULL) {
    // Obtain the pthread minstack size by calling __pthread_get_minstack.
    size_t minstack_size = _get_minstack_func(attr);

    // Remove non-TLS area size included in minstack size returned
    // by __pthread_get_minstack() to get the static TLS size.
    // In glibc before 2.27, minstack size includes guard_size.
    // In glibc 2.27 and later, guard_size is automatically added
    // to the stack size by pthread_create and is no longer included
    // in minstack size. In both cases, the guard_size is taken into
    // account, so there is no need to adjust the result for that.
    //
    // Although __pthread_get_minstack() is a private glibc function,
    // it is expected to have a stable behavior across future glibc
    // versions while glibc still allocates the static TLS blocks off
    // the stack. Following is glibc 2.28 __pthread_get_minstack():
    //
    // size_t
    // __pthread_get_minstack (const pthread_attr_t *attr)
    // {
    //   return GLRO(dl_pagesize) + __static_tls_size + PTHREAD_STACK_MIN;
    // }
    //
    //
    // The following 'minstack_size > os::vm_page_size() + PTHREAD_STACK_MIN'
    // if check is done for precaution.
    if (minstack_size > (size_t)os::vm_page_size() + PTHREAD_STACK_MIN) {
      tls_size = minstack_size - os::vm_page_size() - PTHREAD_STACK_MIN;
    }
  }

  log_info(os, thread)("Stack size adjustment for TLS is " SIZE_FORMAT,
                       tls_size);
  return tls_size;
}

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

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

  // Calculate stack size if it's not specified by caller.
  size_t stack_size = os::Posix::get_initial_stack_size(thr_type, req_stack_size);
  // In glibc versions prior to 2.27 the guard size mechanism
  // is not implemented properly. The posix standard requires adding
  // the size of the guard pages to the stack size, instead Linux
  // takes the space out of 'stacksize'. Thus we adapt the requested
  // stack_size by the size of the guard pages to mimic proper
  // behaviour. However, be careful not to end up with a size
  // of zero due to overflow. Don't add the guard page in that case.
  size_t guard_size = os::Linux::default_guard_size(thr_type);
  // Configure glibc guard page. Must happen before calling
  // get_static_tls_area_size(), which uses the guard_size.
  pthread_attr_setguardsize(&attr, guard_size);

  size_t stack_adjust_size = 0;
  if (AdjustStackSizeForTLS) {
    // Adjust the stack_size for on-stack TLS - see get_static_tls_area_size().
    stack_adjust_size += get_static_tls_area_size(&attr);
  } else {
    stack_adjust_size += guard_size;
  }

  stack_adjust_size = align_up(stack_adjust_size, os::vm_page_size());
  if (stack_size <= SIZE_MAX - stack_adjust_size) {
    stack_size += stack_adjust_size;
  }
  assert(is_aligned(stack_size, os::vm_page_size()), "stack_size not aligned");

  int status = pthread_attr_setstacksize(&attr, stack_size);
  if (status != 0) {
    // pthread_attr_setstacksize() function can fail
    // if the stack size exceeds a system-imposed limit.
    assert_status(status == EINVAL, status, "pthread_attr_setstacksize");
    log_warning(os, thread)("The %sthread stack size specified is invalid: " SIZE_FORMAT "k",
                            (thr_type == compiler_thread) ? "compiler " : ((thr_type == java_thread) ? "" : "VM "),
                            stack_size / K);
    thread->set_osthread(NULL);
    delete osthread;
    return false;
  }

  ThreadState state;

  {
    ResourceMark rm;
    pthread_t tid;
    int ret = 0;
    int limit = 3;
    do {
      ret = pthread_create(&tid, &attr, (void* (*)(void*)) thread_native_entry, thread);
    } while (ret == EAGAIN && limit-- > 0);

    char buf[64];
    if (ret == 0) {
      log_info(os, thread)("Thread \"%s\" started (pthread id: " UINTX_FORMAT ", attributes: %s). ",
                           thread->name(), (uintx) tid, os::Posix::describe_pthread_attr(buf, sizeof(buf), &attr));
    } else {
      log_warning(os, thread)("Failed to start thread \"%s\" - pthread_create failed (%s) for attributes: %s.",
                              thread->name(), os::errno_name(ret), os::Posix::describe_pthread_attr(buf, sizeof(buf), &attr));
      // Log some OS information which might explain why creating the thread failed.
      log_info(os, thread)("Number of threads approx. running in the VM: %d", Threads::number_of_threads());
      LogStream st(Log(os, thread)::info());
      os::Posix::print_rlimit_info(&st);
      os::print_memory_info(&st);
      os::Linux::print_proc_sys_info(&st);
      os::Linux::print_container_info(&st);
    }

    pthread_attr_destroy(&attr);

    if (ret != 0) {
      // Need to clean up stuff we've allocated so far
      thread->set_osthread(NULL);
      delete osthread;
      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();
      MutexLocker ml(sync_with_child, Mutex::_no_safepoint_check_flag);
      while ((state = osthread->get_state()) == ALLOCATED) {
        sync_with_child->wait_without_safepoint_check();
      }
    }
  }

  // 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();

  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::is_primordial_thread()) {
    // If current thread is primordial 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.

    StackOverflow* overflow_state = thread->stack_overflow_state();
    address addr = overflow_state->stack_reserved_zone_base();
    assert(addr != NULL, "initialization problem?");
    assert(overflow_state->stack_available(addr) > 0, "stack guard should not be enabled");

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

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

  log_info(os, thread)("Thread attached (tid: " UINTX_FORMAT ", pthread id: " UINTX_FORMAT
                       ", stack: " PTR_FORMAT " - " PTR_FORMAT " (" SIZE_FORMAT "k) ).",
                       os::current_thread_id(), (uintx) pthread_self(),
                       p2i(thread->stack_base()), p2i(thread->stack_end()), thread->stack_size());

  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();
  MutexLocker 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");

  // We are told to free resources of the argument thread,
  // but we can only really operate on the current thread.
  assert(Thread::current()->osthread() == osthread,
         "os::free_thread but not current thread");

#ifdef ASSERT
  sigset_t current;
  sigemptyset(¤t);
  pthread_sigmask(SIG_SETMASK, NULL, ¤t);
  assert(!sigismember(¤t, PosixSignals::SR_signum), "SR signal should not be blocked!");
#endif

  // Restore caller's signal mask
  sigset_t sigmask = osthread->caller_sigmask();
  pthread_sigmask(SIG_SETMASK, &sigmask, NULL);

  delete osthread;
}

//////////////////////////////////////////////////////////////////////////////
// primordial thread

// Check if current thread is the primordial thread, similar to Solaris thr_main.
bool os::is_primordial_thread(void) {
  if (suppress_primordial_thread_resolution) {
    return false;
  }
  char dummy;
  // If called before init complete, thread stack bottom will be null.
  // Can be called if fatal error occurs before initialization.
  if (os::Linux::initial_thread_stack_bottom() == NULL) return false;
  assert(os::Linux::initial_thread_stack_bottom() != NULL &&
         os::Linux::initial_thread_stack_size()   != 0,
         "os::init did not locate primordial thread's stack region");
  if ((address)&dummy >= os::Linux::initial_thread_stack_bottom() &&
      (address)&dummy < os::Linux::initial_thread_stack_bottom() +
                        os::Linux::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 = os::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 primordial thread stack. This special handling of primordial thread stack
// is needed because pthread_getattr_np() on most (all?) Linux distros returns
// bogus value for the primordial process thread. While the launcher has created
// the VM in a new thread since JDK 6, we still have to allow for the use of the
// JNI invocation API from a primordial thread.
void os::Linux::capture_initial_stack(size_t max_size) {

  // max_size is either 0 (which means accept OS default for thread stacks) or
  // a user-specified value known to be at least the minimum needed. If we
  // are actually on the primordial thread we can make it appear that we have a
  // smaller max_size stack by inserting the guard pages at that location. But we
  // cannot do anything to emulate a larger stack than what has been provided by
  // the OS or threading library. In fact if we try to use a stack greater than
  // what is set by rlimit then we will crash the hosting process.

  // Maximum stack size is the easy part, get it from RLIMIT_STACK.
  // If this is "unlimited" then it will be a huge value.
  struct rlimit rlim;
  getrlimit(RLIMIT_STACK, &rlim);
  size_t 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.
  //   But ensure we don't underflow the stack size - allow 1 page spare
  if (stack_size >= (size_t)(3 * os::vm_page_size())) {
    stack_size -= 2 * os::vm_page_size();
  }

  // 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 = os::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 (s && 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 primordial thread, good luck in the
        // embedded case.
        warning("Can't detect primordial 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 primordial 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 primordial 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 * os::vm_page_size();
  }

  // stack_top could be partially down the page so align it
  stack_top = align_up(stack_top, os::vm_page_size());

  // Allowed stack value is minimum of max_size and what we derived from rlimit
  if (max_size > 0) {
    _initial_thread_stack_size = MIN2(max_size, stack_size);
  } else {
    // Accept the rlimit max, but if stack is unlimited then it will be huge, so
    // clamp it at 8MB as we do on Solaris
    _initial_thread_stack_size = MIN2(stack_size, 8*M);
  }
  _initial_thread_stack_size = align_down(_initial_thread_stack_size, os::vm_page_size());
  _initial_thread_stack_bottom = (address)stack_top - _initial_thread_stack_size;

  assert(_initial_thread_stack_bottom < (address)stack_top, "overflow!");

  if (log_is_enabled(Info, os, thread)) {
    // See if we seem to be on primordial process thread
    bool primordial = uintptr_t(&rlim) > uintptr_t(_initial_thread_stack_bottom) &&
                      uintptr_t(&rlim) < stack_top;

    log_info(os, thread)("Capturing initial stack in %s thread: req. size: " SIZE_FORMAT "K, actual size: "
                         SIZE_FORMAT "K, top=" INTPTR_FORMAT ", bottom=" INTPTR_FORMAT,
                         primordial ? "primordial" : "user", max_size / K,  _initial_thread_stack_size / K,
                         stack_top, intptr_t(_initial_thread_stack_bottom));
  }
}

////////////////////////////////////////////////////////////////////////////////
// time support
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();
  }
}

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 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 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 &&
      clock_getres(clockid, &tp) == 0 && tp.tv_sec == 0) {
    _supports_fast_thread_cpu_time = true;
    _pthread_getcpuclockid = pthread_getcpuclockid_func;
  }
}

// thread_id is kernel thread id (similar to Solaris LWP id)
intx os::current_thread_id() { return os::Linux::gettid(); }
int os::current_process_id() {
  return ::getpid();
}

// DLL functions

// 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"; }

// check if addr is inside libjvm.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,
                                      bool demangle) {
  // 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 (!(demangle && 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, demangle)) {
        return true;
      }
    }
  }

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

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 != nullptr, "sanity check");

  Dl_info dlinfo;
  if (dladdr((void*)addr, &dlinfo) != 0) {
    if (dlinfo.dli_fname != nullptr) {
      jio_snprintf(buf, buflen, "%s", dlinfo.dli_fname);
    }
    if (dlinfo.dli_fbase != nullptr && offset != nullptr) {
      *offset = addr - (address)dlinfo.dli_fbase;
    }
    return true;
  }
  buf[0] = '\0';
  if (offset) *offset = -1;
  return false;
}

// 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;

  log_info(os)("attempting shared library load of %s", filename);

  // 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) {
    if (!ElfFile::specifies_noexecstack(filename)) {
      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.
        //
        // Dynamic loader will make all stacks executable after
        // this function returns, and will not do that again.
        assert(Threads::number_of_threads() == 0, "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 ', or link it with '-z noexecstack'.",
                filename);

        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;
  }

  if (elf_head.e_ident[EI_DATA] != LITTLE_ENDIAN_ONLY(ELFDATA2LSB) BIG_ENDIAN_ONLY(ELFDATA2MSB)) {
    // handle invalid/out of range endianness values
    if (elf_head.e_ident[EI_DATA] == 0 || elf_head.e_ident[EI_DATA] > 2) {
      return NULL;
    }

#if defined(VM_LITTLE_ENDIAN)
    // VM is LE, shared object BE
    elf_head.e_machine = be16toh(elf_head.e_machine);
#else
    // VM is BE, shared object LE
    elf_head.e_machine = le16toh(elf_head.e_machine);
#endif
  }

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

#ifndef EM_AARCH64
  #define EM_AARCH64    183               /* ARM AARCH64 */
#endif
#ifndef EM_RISCV
  #define EM_RISCV      243               /* RISC-V */
#endif
#ifndef EM_LOONGARCH
  #define EM_LOONGARCH  258               /* LoongArch */
#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 LE"},
    {EM_SH,          EM_SH,      ELFCLASS32, ELFDATA2LSB, (char*)"SuperH"},
#else
    {EM_PPC64,       EM_PPC64,   ELFCLASS64, ELFDATA2MSB, (char*)"Power PC 64"},
    {EM_SH,          EM_SH,      ELFCLASS32, ELFDATA2MSB, (char*)"SuperH BE"},
#endif
    {EM_ARM,         EM_ARM,     ELFCLASS32, ELFDATA2LSB, (char*)"ARM"},
    // we only support 64 bit z architecture
    {EM_S390,        EM_S390,    ELFCLASS64, 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"},
    {EM_AARCH64,     EM_AARCH64, ELFCLASS64, ELFDATA2LSB, (char*)"AARCH64"},
#ifdef _LP64
    {EM_RISCV,       EM_RISCV,   ELFCLASS64, ELFDATA2LSB, (char*)"RISCV64"},
#else
    {EM_RISCV,       EM_RISCV,   ELFCLASS32, ELFDATA2LSB, (char*)"RISCV32"},
#endif
    {EM_LOONGARCH,   EM_LOONGARCH, ELFCLASS64, ELFDATA2LSB, (char*)"LoongArch"},
  };

#if  (defined IA32)
  static  Elf32_Half running_arch_code=EM_386;
#elif   (defined AMD64) || (defined X32)
  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 AARCH64)
  static  Elf32_Half running_arch_code=EM_AARCH64;
#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;
#elif  (defined SH)
  static  Elf32_Half running_arch_code=EM_SH;
#elif  (defined RISCV)
  static  Elf32_Half running_arch_code=EM_RISCV;
#elif  (defined LOONGARCH)
  static  Elf32_Half running_arch_code=EM_LOONGARCH;
#else
    #error Method os::dll_load requires that one of following is defined:\
        AARCH64, ALPHA, ARM, AMD64, IA32, IA64, LOONGARCH, M68K, MIPS, MIPSEL, PARISC, __powerpc__, __powerpc64__, RISCV, S390, SH, __sparc
#endif

  // Identify compatibility 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.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 .so on a %s 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 platform)",
                 lib_arch.code, arch_array[running_arch_index].name);
    }
    return NULL;
  }

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

  // ELF file class/capacity : 0 - invalid, 1 - 32bit, 2 - 64bit
  if (lib_arch.elf_class > 2 || lib_arch.elf_class < 1) {
    ::snprintf(diag_msg_buf, diag_msg_max_length-1, " (Possible cause: invalid ELF file class)");
    return NULL;
  }

  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, can't load %d-bit .so on a %d-bit platform)",
               (int) lib_arch.elf_class * 32, arch_array[running_arch_index].elf_class * 32);
    return NULL;
  }

  return NULL;
}

void * os::Linux::dlopen_helper(const char *filename, char *ebuf,
                                int ebuflen) {
  void * result = ::dlopen(filename, RTLD_LAZY);
  if (result == NULL) {
    const char* error_report = ::dlerror();
    if (error_report == NULL) {
      error_report = "dlerror returned no error description";
    }
    if (ebuf != NULL && ebuflen > 0) {
      ::strncpy(ebuf, error_report, ebuflen-1);
      ebuf[ebuflen-1]='\0';
    }
    Events::log_dll_message(NULL, "Loading shared library %s failed, %s", filename, error_report);
    log_info(os)("shared library load of %s failed, %s", filename, error_report);
  } else {
    Events::log_dll_message(NULL, "Loaded shared library %s", filename);
    log_info(os)("shared library load of %s was successful", filename);
  }
  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) {
    for (JavaThreadIteratorWithHandle jtiwh; JavaThread *jt = jtiwh.next(); ) {
      StackOverflow* overflow_state = jt->stack_overflow_state();
      if (!overflow_state->stack_guard_zone_unused() &&     // Stack not yet fully initialized
          overflow_state->stack_guards_enabled()) {         // No pending stack overflow exceptions
        if (!os::guard_memory((char *)jt->stack_end(), StackOverflow::stack_guard_zone_size())) {
          warning("Attempt to reguard stack yellow zone failed.");
        }
      }
    }
  }

  return result;
}

const char* os::Linux::dll_path(void* lib) {
  struct link_map *lmap;
  const char* l_path = NULL;
  assert(lib != NULL, "dll_path parameter must not be NULL");

  int res_dli = ::dlinfo(lib, RTLD_DI_LINKMAP, &lmap);
  if (res_dli == 0) {
    l_path = lmap->l_name;
  }
  return l_path;
}

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

  if (hdr != NULL) {
    st->print_cr("%s", hdr);
  }

  char buf[33];
  int bytes;
  buf[32] = '\0';
  while ((bytes = ::read(fd, buf, sizeof(buf)-1)) > 0) {
    st->print_raw(buf, bytes);
  }

  ::close(fd);

  return true;
}

static void _print_ascii_file_h(const char* header, const char* filename, outputStream* st, bool same_line = true) {
  st->print("%s:%c", header, same_line ? ' ' : '\n');
  if (!_print_ascii_file(filename, st)) {
    st->print_cr("");
  }
}

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_cr("Can not get library information for pid = %d", pid);
  }
}

struct loaded_modules_info_param {
  os::LoadedModulesCallbackFunc callback;
  void *param;
};

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