Mercurial > jdk8-mips64-public > hotspot / file revision

 /*

  * Copyright (c) 1999, 2012, 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 "assembler_x86.inline.hpp"

 #include "classfile/classLoader.hpp"

 #include "classfile/systemDictionary.hpp"

 #include "classfile/vmSymbols.hpp"

 #include "code/icBuffer.hpp"

 #include "code/vtableStubs.hpp"

 #include "interpreter/interpreter.hpp"

 #include "jvm_linux.h"

 #include "memory/allocation.inline.hpp"

 #include "mutex_linux.inline.hpp"

 #include "nativeInst_x86.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/frame.inline.hpp"

 #include "runtime/interfaceSupport.hpp"

 #include "runtime/java.hpp"

 #include "runtime/javaCalls.hpp"

 #include "runtime/mutexLocker.hpp"

 #include "runtime/osThread.hpp"

 #include "runtime/sharedRuntime.hpp"

 #include "runtime/stubRoutines.hpp"

 #include "runtime/thread.inline.hpp"

 #include "runtime/timer.hpp"

 #include "utilities/events.hpp"

 #include "utilities/vmError.hpp"

 // put OS-includes here

 # include <sys/types.h>

 # include <sys/mman.h>

 # include <pthread.h>

 # include <signal.h>

 # include <errno.h>

 # include <dlfcn.h>

 # include <stdlib.h>

 # include <stdio.h>

 # include <unistd.h>

 # include <sys/resource.h>

 # include <pthread.h>

 # include <sys/stat.h>

 # include <sys/time.h>

 # include <sys/utsname.h>

 # include <sys/socket.h>

 # include <sys/wait.h>

 # include <pwd.h>

 # include <poll.h>

 # include <ucontext.h>

 # include <fpu_control.h>

 #ifdef AMD64

 #define REG_SP REG_RSP

 #define REG_PC REG_RIP

 #define REG_FP REG_RBP

 #define SPELL_REG_SP "rsp"

 #define SPELL_REG_FP "rbp"

 #else

 #define REG_SP REG_UESP

 #define REG_PC REG_EIP

 #define REG_FP REG_EBP

 #define SPELL_REG_SP "esp"

 #define SPELL_REG_FP "ebp"

 #endif // AMD64

 address os::current_stack_pointer() {

 #ifdef SPARC_WORKS

   register void *esp;

   __asm__("mov %%"SPELL_REG_SP", %0":"=r"(esp));

   return (address) ((char*)esp + sizeof(long)*2);

 #else

   register void *esp __asm__ (SPELL_REG_SP);

   return (address) esp;

 #endif

 }

 char* os::non_memory_address_word() {

   // Must never look like an address returned by reserve_memory,

   // even in its subfields (as defined by the CPU immediate fields,

   // if the CPU splits constants across multiple instructions).

   return (char*) -1;

 }

 void os::initialize_thread(Thread* thr) {

 // Nothing to do.

 }

 address os::Linux::ucontext_get_pc(ucontext_t * uc) {

   return (address)uc->uc_mcontext.gregs[REG_PC];

 }

 intptr_t* os::Linux::ucontext_get_sp(ucontext_t * uc) {

   return (intptr_t*)uc->uc_mcontext.gregs[REG_SP];

 }

 intptr_t* os::Linux::ucontext_get_fp(ucontext_t * uc) {

   return (intptr_t*)uc->uc_mcontext.gregs[REG_FP];

 }

 // For Forte Analyzer AsyncGetCallTrace profiling support - thread

 // is currently interrupted by SIGPROF.

 // os::Solaris::fetch_frame_from_ucontext() tries to skip nested signal

 // frames. Currently we don't do that on Linux, so it's the same as

 // os::fetch_frame_from_context().

 ExtendedPC os::Linux::fetch_frame_from_ucontext(Thread* thread,

   ucontext_t* uc, intptr_t** ret_sp, intptr_t** ret_fp) {

   assert(thread != NULL, "just checking");

   assert(ret_sp != NULL, "just checking");

   assert(ret_fp != NULL, "just checking");

   return os::fetch_frame_from_context(uc, ret_sp, ret_fp);

 }

 ExtendedPC os::fetch_frame_from_context(void* ucVoid,

                     intptr_t** ret_sp, intptr_t** ret_fp) {

   ExtendedPC  epc;

   ucontext_t* uc = (ucontext_t*)ucVoid;

   if (uc != NULL) {

     epc = ExtendedPC(os::Linux::ucontext_get_pc(uc));

     if (ret_sp) *ret_sp = os::Linux::ucontext_get_sp(uc);

     if (ret_fp) *ret_fp = os::Linux::ucontext_get_fp(uc);

   } else {

     // construct empty ExtendedPC for return value checking

     epc = ExtendedPC(NULL);

     if (ret_sp) *ret_sp = (intptr_t *)NULL;

     if (ret_fp) *ret_fp = (intptr_t *)NULL;

   }

   return epc;

 }

 frame os::fetch_frame_from_context(void* ucVoid) {

   intptr_t* sp;

   intptr_t* fp;

   ExtendedPC epc = fetch_frame_from_context(ucVoid, &sp, &fp);

   return frame(sp, fp, epc.pc());

 }

 // By default, gcc always save frame pointer (%ebp/%rbp) on stack. It may get

 // turned off by -fomit-frame-pointer,

 frame os::get_sender_for_C_frame(frame* fr) {

   return frame(fr->sender_sp(), fr->link(), fr->sender_pc());

 }

 intptr_t* _get_previous_fp() {

 #ifdef SPARC_WORKS

   register intptr_t **ebp;

   __asm__("mov %%"SPELL_REG_FP", %0":"=r"(ebp));

 #else

   register intptr_t **ebp __asm__ (SPELL_REG_FP);

 #endif

   return (intptr_t*) *ebp;   // we want what it points to.

 }

 frame os::current_frame() {

   intptr_t* fp = _get_previous_fp();

   frame myframe((intptr_t*)os::current_stack_pointer(),

                 (intptr_t*)fp,

                 CAST_FROM_FN_PTR(address, os::current_frame));

   if (os::is_first_C_frame(&myframe)) {

     // stack is not walkable

     return frame(NULL, NULL, NULL);

   } else {

     return os::get_sender_for_C_frame(&myframe);

   }

 }

 // Utility functions

 // From IA32 System Programming Guide

 enum {

   trap_page_fault = 0xE

 };

 extern "C" void Fetch32PFI () ;

 extern "C" void Fetch32Resume () ;

 #ifdef AMD64

 extern "C" void FetchNPFI () ;

 extern "C" void FetchNResume () ;

 #endif // AMD64

 extern "C" JNIEXPORT int

 JVM_handle_linux_signal(int sig,

                         siginfo_t* info,

                         void* ucVoid,

                         int abort_if_unrecognized) {

   ucontext_t* uc = (ucontext_t*) ucVoid;

   Thread* t = ThreadLocalStorage::get_thread_slow();

   SignalHandlerMark shm(t);

   // Note: it's not uncommon that JNI code uses signal/sigset to install

   // then restore certain signal handler (e.g. to temporarily block SIGPIPE,

   // or have a SIGILL handler when detecting CPU type). When that happens,

   // JVM_handle_linux_signal() might be invoked with junk info/ucVoid. To

   // avoid unnecessary crash when libjsig is not preloaded, try handle signals

   // that do not require siginfo/ucontext first.

   if (sig == SIGPIPE || sig == SIGXFSZ) {

     // allow chained handler to go first

     if (os::Linux::chained_handler(sig, info, ucVoid)) {

       return true;

     } else {

       if (PrintMiscellaneous && (WizardMode || Verbose)) {

         char buf[64];

         warning("Ignoring %s - see bugs 4229104 or 646499219",

                 os::exception_name(sig, buf, sizeof(buf)));

       }

       return true;

     }

   }

   JavaThread* thread = NULL;

   VMThread* vmthread = NULL;

   if (os::Linux::signal_handlers_are_installed) {

     if (t != NULL ){

       if(t->is_Java_thread()) {

         thread = (JavaThread*)t;

       }

       else if(t->is_VM_thread()){

         vmthread = (VMThread *)t;

       }

     }

   }

 /*

   NOTE: does not seem to work on linux.

   if (info == NULL || info->si_code <= 0 || info->si_code == SI_NOINFO) {

     // can't decode this kind of signal

     info = NULL;

   } else {

     assert(sig == info->si_signo, "bad siginfo");

   }

 */

   // decide if this trap can be handled by a stub

   address stub = NULL;

   address pc          = NULL;

   //%note os_trap_1

   if (info != NULL && uc != NULL && thread != NULL) {

     pc = (address) os::Linux::ucontext_get_pc(uc);

     if (pc == (address) Fetch32PFI) {

        uc->uc_mcontext.gregs[REG_PC] = intptr_t(Fetch32Resume) ;

        return 1 ;

     }

 #ifdef AMD64

     if (pc == (address) FetchNPFI) {

        uc->uc_mcontext.gregs[REG_PC] = intptr_t (FetchNResume) ;

        return 1 ;

     }

 #endif // AMD64

     // Handle ALL stack overflow variations here

     if (sig == SIGSEGV) {

       address addr = (address) info->si_addr;

       // check if fault address is within thread stack

       if (addr < thread->stack_base() &&

           addr >= thread->stack_base() - thread->stack_size()) {

         // stack overflow

         if (thread->in_stack_yellow_zone(addr)) {

           thread->disable_stack_yellow_zone();

           if (thread->thread_state() == _thread_in_Java) {

             // Throw a stack overflow exception.  Guard pages will be reenabled

             // while unwinding the stack.

             stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::STACK_OVERFLOW);

           } else {

             // Thread was in the vm or native code.  Return and try to finish.

             return 1;

           }

         } else if (thread->in_stack_red_zone(addr)) {

           // Fatal red zone violation.  Disable the guard pages and fall through

           // to handle_unexpected_exception way down below.

           thread->disable_stack_red_zone();

           tty->print_raw_cr("An irrecoverable stack overflow has occurred.");

         } else {

           // Accessing stack address below sp may cause SEGV if current

           // thread has MAP_GROWSDOWN stack. This should only happen when

           // current thread was created by user code with MAP_GROWSDOWN flag

           // and then attached to VM. See notes in os_linux.cpp.

           if (thread->osthread()->expanding_stack() == 0) {

              thread->osthread()->set_expanding_stack();

              if (os::Linux::manually_expand_stack(thread, addr)) {

                thread->osthread()->clear_expanding_stack();

                return 1;

              }

              thread->osthread()->clear_expanding_stack();

           } else {

              fatal("recursive segv. expanding stack.");

           }

         }

       }

     }

     if (thread->thread_state() == _thread_in_Java) {

       // Java thread running in Java code => find exception handler if any

       // a fault inside compiled code, the interpreter, or a stub

       if (sig == SIGSEGV && os::is_poll_address((address)info->si_addr)) {

         stub = SharedRuntime::get_poll_stub(pc);

       } else if (sig == SIGBUS /* && info->si_code == BUS_OBJERR */) {

         // BugId 4454115: A read from a MappedByteBuffer can fault

         // here if the underlying file has been truncated.

         // Do not crash the VM in such a case.

         CodeBlob* cb = CodeCache::find_blob_unsafe(pc);

         nmethod* nm = cb->is_nmethod() ? (nmethod*)cb : NULL;

         if (nm != NULL && nm->has_unsafe_access()) {

           stub = StubRoutines::handler_for_unsafe_access();

         }

       }

       else

 #ifdef AMD64

       if (sig == SIGFPE  &&

           (info->si_code == FPE_INTDIV || info->si_code == FPE_FLTDIV)) {

         stub =

           SharedRuntime::

           continuation_for_implicit_exception(thread,

                                               pc,

                                               SharedRuntime::

                                               IMPLICIT_DIVIDE_BY_ZERO);

 #else

       if (sig == SIGFPE /* && info->si_code == FPE_INTDIV */) {

         // HACK: si_code does not work on linux 2.2.12-20!!!

         int op = pc[0];

         if (op == 0xDB) {

           // FIST

           // TODO: The encoding of D2I in i486.ad can cause an exception

           // prior to the fist instruction if there was an invalid operation

           // pending. We want to dismiss that exception. From the win_32

           // side it also seems that if it really was the fist causing

           // the exception that we do the d2i by hand with different

           // rounding. Seems kind of weird.

           // NOTE: that we take the exception at the NEXT floating point instruction.

           assert(pc[0] == 0xDB, "not a FIST opcode");

           assert(pc[1] == 0x14, "not a FIST opcode");

           assert(pc[2] == 0x24, "not a FIST opcode");

           return true;

         } else if (op == 0xF7) {

           // IDIV

           stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_DIVIDE_BY_ZERO);

         } else {

           // TODO: handle more cases if we are using other x86 instructions

           //   that can generate SIGFPE signal on linux.

           tty->print_cr("unknown opcode 0x%X with SIGFPE.", op);

           fatal("please update this code.");

         }

 #endif // AMD64

       } else if (sig == SIGSEGV &&

                !MacroAssembler::needs_explicit_null_check((intptr_t)info->si_addr)) {

           // Determination of interpreter/vtable stub/compiled code null exception

           stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_NULL);

       }

     } else if (thread->thread_state() == _thread_in_vm &&

                sig == SIGBUS && /* info->si_code == BUS_OBJERR && */

                thread->doing_unsafe_access()) {

         stub = StubRoutines::handler_for_unsafe_access();

     }

     // jni_fast_Get<Primitive>Field can trap at certain pc's if a GC kicks in

     // and the heap gets shrunk before the field access.

     if ((sig == SIGSEGV) || (sig == SIGBUS)) {

       address addr = JNI_FastGetField::find_slowcase_pc(pc);

       if (addr != (address)-1) {

         stub = addr;

       }

     }

     // Check to see if we caught the safepoint code in the

     // process of write protecting the memory serialization page.

     // It write enables the page immediately after protecting it

     // so we can just return to retry the write.

     if ((sig == SIGSEGV) &&

         os::is_memory_serialize_page(thread, (address) info->si_addr)) {

       // Block current thread until the memory serialize page permission restored.

       os::block_on_serialize_page_trap();

       return true;

     }

   }

 #ifndef AMD64

   // Execution protection violation

   //

   // This should be kept as the last step in the triage.  We don't

   // have a dedicated trap number for a no-execute fault, so be

   // conservative and allow other handlers the first shot.

   //

   // Note: We don't test that info->si_code == SEGV_ACCERR here.

   // this si_code is so generic that it is almost meaningless; and

   // the si_code for this condition may change in the future.

   // Furthermore, a false-positive should be harmless.

   if (UnguardOnExecutionViolation > 0 &&

       (sig == SIGSEGV || sig == SIGBUS) &&

       uc->uc_mcontext.gregs[REG_TRAPNO] == trap_page_fault) {

     int page_size = os::vm_page_size();

     address addr = (address) info->si_addr;

     address pc = os::Linux::ucontext_get_pc(uc);

     // Make sure the pc and the faulting address are sane.

     //

     // If an instruction spans a page boundary, and the page containing

     // the beginning of the instruction is executable but the following

     // page is not, the pc and the faulting address might be slightly

     // different - we still want to unguard the 2nd page in this case.

     //

     // 15 bytes seems to be a (very) safe value for max instruction size.

     bool pc_is_near_addr =

       (pointer_delta((void*) addr, (void*) pc, sizeof(char)) < 15);

     bool instr_spans_page_boundary =

       (align_size_down((intptr_t) pc ^ (intptr_t) addr,

                        (intptr_t) page_size) > 0);

     if (pc == addr || (pc_is_near_addr && instr_spans_page_boundary)) {

       static volatile address last_addr =

         (address) os::non_memory_address_word();

       // In conservative mode, don't unguard unless the address is in the VM

       if (addr != last_addr &&

           (UnguardOnExecutionViolation > 1 || os::address_is_in_vm(addr))) {

         // Set memory to RWX and retry

         address page_start =

           (address) align_size_down((intptr_t) addr, (intptr_t) page_size);

         bool res = os::protect_memory((char*) page_start, page_size,

                                       os::MEM_PROT_RWX);

         if (PrintMiscellaneous && Verbose) {

           char buf[256];

           jio_snprintf(buf, sizeof(buf), "Execution protection violation "

                        "at " INTPTR_FORMAT

                        ", unguarding " INTPTR_FORMAT ": %s, errno=%d", addr,

                        page_start, (res ? "success" : "failed"), errno);

           tty->print_raw_cr(buf);

         }

         stub = pc;

         // Set last_addr so if we fault again at the same address, we don't end

         // up in an endless loop.

         //

         // There are two potential complications here.  Two threads trapping at

         // the same address at the same time could cause one of the threads to

         // think it already unguarded, and abort the VM.  Likely very rare.

         //

         // The other race involves two threads alternately trapping at

         // different addresses and failing to unguard the page, resulting in

         // an endless loop.  This condition is probably even more unlikely than

         // the first.

         //

         // Although both cases could be avoided by using locks or thread local

         // last_addr, these solutions are unnecessary complication: this

         // handler is a best-effort safety net, not a complete solution.  It is

         // disabled by default and should only be used as a workaround in case

         // we missed any no-execute-unsafe VM code.

         last_addr = addr;

       }

     }

   }

 #endif // !AMD64

   if (stub != NULL) {

     // save all thread context in case we need to restore it

     if (thread != NULL) thread->set_saved_exception_pc(pc);

     uc->uc_mcontext.gregs[REG_PC] = (greg_t)stub;

     return true;

   }

   // signal-chaining

   if (os::Linux::chained_handler(sig, info, ucVoid)) {

      return true;

   }

   if (!abort_if_unrecognized) {

     // caller wants another chance, so give it to him

     return false;

   }

   if (pc == NULL && uc != NULL) {

     pc = os::Linux::ucontext_get_pc(uc);

   }

   // unmask current signal

   sigset_t newset;

   sigemptyset(&newset);

   sigaddset(&newset, sig);

   sigprocmask(SIG_UNBLOCK, &newset, NULL);

   VMError err(t, sig, pc, info, ucVoid);

   err.report_and_die();

   ShouldNotReachHere();

 }

 void os::Linux::init_thread_fpu_state(void) {

 #ifndef AMD64

   // set fpu to 53 bit precision

   set_fpu_control_word(0x27f);

 #endif // !AMD64

 }

 int os::Linux::get_fpu_control_word(void) {

 #ifdef AMD64

   return 0;

 #else

   int fpu_control;

   _FPU_GETCW(fpu_control);

   return fpu_control & 0xffff;

 #endif // AMD64

 }

 void os::Linux::set_fpu_control_word(int fpu_control) {

 #ifndef AMD64

   _FPU_SETCW(fpu_control);

 #endif // !AMD64

 }

 // Check that the linux kernel version is 2.4 or higher since earlier

 // versions do not support SSE without patches.

 bool os::supports_sse() {

 #ifdef AMD64

   return true;

 #else

   struct utsname uts;

   if( uname(&uts) != 0 ) return false; // uname fails?

   char *minor_string;

   int major = strtol(uts.release,&minor_string,10);

   int minor = strtol(minor_string+1,NULL,10);

   bool result = (major > 2 || (major==2 && minor >= 4));

 #ifndef PRODUCT

   if (PrintMiscellaneous && Verbose) {

     tty->print("OS version is %d.%d, which %s support SSE/SSE2\n",

                major,minor, result ? "DOES" : "does NOT");

   }

 #endif

   return result;

 #endif // AMD64

 }

 bool os::is_allocatable(size_t bytes) {

 #ifdef AMD64

   // unused on amd64?

   return true;

 #else

   if (bytes < 2 * G) {

     return true;

   }

   char* addr = reserve_memory(bytes, NULL);

   if (addr != NULL) {

     release_memory(addr, bytes);

   }

   return addr != NULL;

 #endif // AMD64

 }

 ////////////////////////////////////////////////////////////////////////////////

 // thread stack

 #ifdef AMD64

 size_t os::Linux::min_stack_allowed  = 64 * K;

 // amd64: pthread on amd64 is always in floating stack mode

 bool os::Linux::supports_variable_stack_size() {  return true; }

 #else

 size_t os::Linux::min_stack_allowed  =  (48 DEBUG_ONLY(+4))*K;

 #ifdef __GNUC__

 #define GET_GS() ({int gs; __asm__ volatile("movw %%gs, %w0":"=q"(gs)); gs&0xffff;})

 #endif

 // Test if pthread library can support variable thread stack size. LinuxThreads

 // in fixed stack mode allocates 2M fixed slot for each thread. LinuxThreads

 // in floating stack mode and NPTL support variable stack size.

 bool os::Linux::supports_variable_stack_size() {

   if (os::Linux::is_NPTL()) {

      // NPTL, yes

      return true;

   } else {

     // Note: We can't control default stack size when creating a thread.

     // If we use non-default stack size (pthread_attr_setstacksize), both

     // floating stack and non-floating stack LinuxThreads will return the

     // same value. This makes it impossible to implement this function by

     // detecting thread stack size directly.

     //

     // An alternative approach is to check %gs. Fixed-stack LinuxThreads

     // do not use %gs, so its value is 0. Floating-stack LinuxThreads use

     // %gs (either as LDT selector or GDT selector, depending on kernel)

     // to access thread specific data.

     //

     // Note that %gs is a reserved glibc register since early 2001, so

     // applications are not allowed to change its value (Ulrich Drepper from

     // Redhat confirmed that all known offenders have been modified to use

     // either %fs or TSD). In the worst case scenario, when VM is embedded in

     // a native application that plays with %gs, we might see non-zero %gs

     // even LinuxThreads is running in fixed stack mode. As the result, we'll

     // return true and skip _thread_safety_check(), so we may not be able to

     // detect stack-heap collisions. But otherwise it's harmless.

     //

 #ifdef __GNUC__

     return (GET_GS() != 0);

 #else

     return false;

 #endif

   }

 }

 #endif // AMD64

 // return default stack size for thr_type

 size_t os::Linux::default_stack_size(os::ThreadType thr_type) {

   // default stack size (compiler thread needs larger stack)

 #ifdef AMD64

   size_t s = (thr_type == os::compiler_thread ? 4 * M : 1 * M);

 #else

   size_t s = (thr_type == os::compiler_thread ? 2 * M : 512 * K);

 #endif // AMD64

   return s;

 }

 size_t os::Linux::default_guard_size(os::ThreadType thr_type) {

   // Creating guard page is very expensive. Java thread has HotSpot

   // guard page, only enable glibc guard page for non-Java threads.

   return (thr_type == java_thread ? 0 : page_size());

 }

 // Java thread:

 //

 //   Low memory addresses

 //    +------------------------+

 //    |                        |\  JavaThread created by VM does not have glibc

 //    |    glibc guard page    | - guard, attached Java thread usually has

 //    |                        |/  1 page glibc guard.

 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()

 //    |                        |\

 //    |  HotSpot Guard Pages   | - red and yellow pages

 //    |                        |/

 //    +------------------------+ JavaThread::stack_yellow_zone_base()

 //    |                        |\

 //    |      Normal Stack      | -

 //    |                        |/

 // P2 +------------------------+ Thread::stack_base()

 //

 // Non-Java thread:

 //

 //   Low memory addresses

 //    +------------------------+

 //    |                        |\

 //    |  glibc guard page      | - usually 1 page

 //    |                        |/

 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()

 //    |                        |\

 //    |      Normal Stack      | -

 //    |                        |/

 // P2 +------------------------+ Thread::stack_base()

 //

 // ** P1 (aka bottom) and size ( P2 = P1 - size) are the address and stack size returned from

 //    pthread_attr_getstack()

 static void current_stack_region(address * bottom, size_t * size) {

   if (os::Linux::is_initial_thread()) {

      // initial thread needs special handling because pthread_getattr_np()

      // may return bogus value.

      *bottom = os::Linux::initial_thread_stack_bottom();

      *size   = os::Linux::initial_thread_stack_size();

   } else {

      pthread_attr_t attr;

      int rslt = pthread_getattr_np(pthread_self(), &attr);

      // JVM needs to know exact stack location, abort if it fails

      if (rslt != 0) {

        if (rslt == ENOMEM) {

          vm_exit_out_of_memory(0, "pthread_getattr_np");

        } else {

          fatal(err_msg("pthread_getattr_np failed with errno = %d", rslt));

        }

      }

      if (pthread_attr_getstack(&attr, (void **)bottom, size) != 0) {

          fatal("Can not locate current stack attributes!");

      }

      pthread_attr_destroy(&attr);

   }

   assert(os::current_stack_pointer() >= *bottom &&

          os::current_stack_pointer() < *bottom + *size, "just checking");

 }

 address os::current_stack_base() {

   address bottom;

   size_t size;

   current_stack_region(&bottom, &size);

   return (bottom + size);

 }

 size_t os::current_stack_size() {

   // stack size includes normal stack and HotSpot guard pages

   address bottom;

   size_t size;

   current_stack_region(&bottom, &size);

   return size;

 }

 /////////////////////////////////////////////////////////////////////////////

 // helper functions for fatal error handler

 void os::print_context(outputStream *st, void *context) {

   if (context == NULL) return;

   ucontext_t *uc = (ucontext_t*)context;

   st->print_cr("Registers:");

 #ifdef AMD64

   st->print(  "RAX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RAX]);

   st->print(", RBX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RBX]);

   st->print(", RCX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RCX]);

   st->print(", RDX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RDX]);

   st->cr();

   st->print(  "RSP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RSP]);

   st->print(", RBP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RBP]);

   st->print(", RSI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RSI]);

   st->print(", RDI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RDI]);

   st->cr();

   st->print(  "R8 =" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R8]);

   st->print(", R9 =" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R9]);

   st->print(", R10=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R10]);

   st->print(", R11=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R11]);

   st->cr();

   st->print(  "R12=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R12]);

   st->print(", R13=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R13]);

   st->print(", R14=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R14]);

   st->print(", R15=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_R15]);

   st->cr();

   st->print(  "RIP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_RIP]);

   st->print(", EFLAGS=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EFL]);

   st->print(", CSGSFS=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_CSGSFS]);

   st->print(", ERR=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_ERR]);

   st->cr();

   st->print("  TRAPNO=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_TRAPNO]);

 #else

   st->print(  "EAX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EAX]);

   st->print(", EBX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EBX]);

   st->print(", ECX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_ECX]);

   st->print(", EDX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EDX]);

   st->cr();

   st->print(  "ESP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_UESP]);

   st->print(", EBP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EBP]);

   st->print(", ESI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_ESI]);

   st->print(", EDI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EDI]);

   st->cr();

   st->print(  "EIP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EIP]);

   st->print(", EFLAGS=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EFL]);

   st->print(", CR2=" INTPTR_FORMAT, uc->uc_mcontext.cr2);

 #endif // AMD64

   st->cr();

   st->cr();

   intptr_t *sp = (intptr_t *)os::Linux::ucontext_get_sp(uc);

   st->print_cr("Top of Stack: (sp=" PTR_FORMAT ")", sp);

   print_hex_dump(st, (address)sp, (address)(sp + 8*sizeof(intptr_t)), sizeof(intptr_t));

   st->cr();

   // Note: it may be unsafe to inspect memory near pc. For example, pc may

   // point to garbage if entry point in an nmethod is corrupted. Leave

   // this at the end, and hope for the best.

   address pc = os::Linux::ucontext_get_pc(uc);

   st->print_cr("Instructions: (pc=" PTR_FORMAT ")", pc);

   print_hex_dump(st, pc - 32, pc + 32, sizeof(char));

 }

 void os::print_register_info(outputStream *st, void *context) {

   if (context == NULL) return;

   ucontext_t *uc = (ucontext_t*)context;

   st->print_cr("Register to memory mapping:");

   st->cr();

   // this is horrendously verbose but the layout of the registers in the

   // context does not match how we defined our abstract Register set, so

   // we can't just iterate through the gregs area

   // this is only for the "general purpose" registers

 #ifdef AMD64

   st->print("RAX="); print_location(st, uc->uc_mcontext.gregs[REG_RAX]);

   st->print("RBX="); print_location(st, uc->uc_mcontext.gregs[REG_RBX]);

   st->print("RCX="); print_location(st, uc->uc_mcontext.gregs[REG_RCX]);

   st->print("RDX="); print_location(st, uc->uc_mcontext.gregs[REG_RDX]);

   st->print("RSP="); print_location(st, uc->uc_mcontext.gregs[REG_RSP]);

   st->print("RBP="); print_location(st, uc->uc_mcontext.gregs[REG_RBP]);

   st->print("RSI="); print_location(st, uc->uc_mcontext.gregs[REG_RSI]);

   st->print("RDI="); print_location(st, uc->uc_mcontext.gregs[REG_RDI]);

   st->print("R8 ="); print_location(st, uc->uc_mcontext.gregs[REG_R8]);

   st->print("R9 ="); print_location(st, uc->uc_mcontext.gregs[REG_R9]);

   st->print("R10="); print_location(st, uc->uc_mcontext.gregs[REG_R10]);

   st->print("R11="); print_location(st, uc->uc_mcontext.gregs[REG_R11]);

   st->print("R12="); print_location(st, uc->uc_mcontext.gregs[REG_R12]);

   st->print("R13="); print_location(st, uc->uc_mcontext.gregs[REG_R13]);

   st->print("R14="); print_location(st, uc->uc_mcontext.gregs[REG_R14]);

   st->print("R15="); print_location(st, uc->uc_mcontext.gregs[REG_R15]);

 #else

   st->print("EAX="); print_location(st, uc->uc_mcontext.gregs[REG_EAX]);

   st->print("EBX="); print_location(st, uc->uc_mcontext.gregs[REG_EBX]);

   st->print("ECX="); print_location(st, uc->uc_mcontext.gregs[REG_ECX]);

   st->print("EDX="); print_location(st, uc->uc_mcontext.gregs[REG_EDX]);

   st->print("ESP="); print_location(st, uc->uc_mcontext.gregs[REG_ESP]);

   st->print("EBP="); print_location(st, uc->uc_mcontext.gregs[REG_EBP]);

   st->print("ESI="); print_location(st, uc->uc_mcontext.gregs[REG_ESI]);

   st->print("EDI="); print_location(st, uc->uc_mcontext.gregs[REG_EDI]);

 #endif // AMD64

   st->cr();

 }

 void os::setup_fpu() {

 #ifndef AMD64

   address fpu_cntrl = StubRoutines::addr_fpu_cntrl_wrd_std();

   __asm__ volatile (  "fldcw (%0)" :

                       : "r" (fpu_cntrl) : "memory");

 #endif // !AMD64

 }

 #ifndef PRODUCT

 void os::verify_stack_alignment() {

 #ifdef AMD64

   assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment");

 #endif

 }

 #endif