1 /*
   2  * Copyright (c) 1997, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * Copyright (c) 2012, 2016 SAP SE. All rights reserved.
   4  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   5  *
   6  * This code is free software; you can redistribute it and/or modify it
   7  * under the terms of the GNU General Public License version 2 only, as
   8  * published by the Free Software Foundation.
   9  *
  10  * This code is distributed in the hope that it will be useful, but WITHOUT
  11  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  12  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  13  * version 2 for more details (a copy is included in the LICENSE file that
  14  * accompanied this code).
  15  *
  16  * You should have received a copy of the GNU General Public License version
  17  * 2 along with this work; if not, write to the Free Software Foundation,
  18  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  19  *
  20  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  21  * or visit www.oracle.com if you need additional information or have any
  22  * questions.
  23  *
  24  */
  25 
  26 // no precompiled headers
  27 #include "asm/assembler.inline.hpp"
  28 #include "classfile/classLoader.hpp"
  29 #include "classfile/systemDictionary.hpp"
  30 #include "classfile/vmSymbols.hpp"
  31 #include "code/codeCache.hpp"
  32 #include "code/icBuffer.hpp"
  33 #include "code/vtableStubs.hpp"
  34 #include "interpreter/interpreter.hpp"
  35 #include "jvm_linux.h"
  36 #include "memory/allocation.inline.hpp"
  37 #include "nativeInst_ppc.hpp"
  38 #include "os_share_linux.hpp"
  39 #include "prims/jniFastGetField.hpp"
  40 #include "prims/jvm.h"
  41 #include "prims/jvm_misc.hpp"
  42 #include "runtime/arguments.hpp"
  43 #include "runtime/extendedPC.hpp"
  44 #include "runtime/frame.inline.hpp"
  45 #include "runtime/interfaceSupport.hpp"
  46 #include "runtime/java.hpp"
  47 #include "runtime/javaCalls.hpp"
  48 #include "runtime/mutexLocker.hpp"
  49 #include "runtime/osThread.hpp"
  50 #include "runtime/sharedRuntime.hpp"
  51 #include "runtime/stubRoutines.hpp"
  52 #include "runtime/thread.inline.hpp"
  53 #include "runtime/timer.hpp"
  54 #include "utilities/events.hpp"
  55 #include "utilities/vmError.hpp"
  56 
  57 // put OS-includes here
  58 # include <sys/types.h>
  59 # include <sys/mman.h>
  60 # include <pthread.h>
  61 # include <signal.h>
  62 # include <errno.h>
  63 # include <dlfcn.h>
  64 # include <stdlib.h>
  65 # include <stdio.h>
  66 # include <unistd.h>
  67 # include <sys/resource.h>
  68 # include <pthread.h>
  69 # include <sys/stat.h>
  70 # include <sys/time.h>
  71 # include <sys/utsname.h>
  72 # include <sys/socket.h>
  73 # include <sys/wait.h>
  74 # include <pwd.h>
  75 # include <poll.h>
  76 # include <ucontext.h>
  77 
  78 
  79 address os::current_stack_pointer() {
  80   intptr_t* csp;
  81 
  82   // inline assembly `mr regno(csp), R1_SP':
  83   __asm__ __volatile__ ("mr %0, 1":"=r"(csp):);
  84 
  85   return (address) csp;
  86 }
  87 
  88 char* os::non_memory_address_word() {
  89   // Must never look like an address returned by reserve_memory,
  90   // even in its subfields (as defined by the CPU immediate fields,
  91   // if the CPU splits constants across multiple instructions).
  92 
  93   return (char*) -1;
  94 }
  95 
  96 void os::initialize_thread(Thread *thread) { }
  97 
  98 // Frame information (pc, sp, fp) retrieved via ucontext
  99 // always looks like a C-frame according to the frame
 100 // conventions in frame_ppc64.hpp.
 101 address os::Linux::ucontext_get_pc(const ucontext_t * uc) {
 102   // On powerpc64, ucontext_t is not selfcontained but contains
 103   // a pointer to an optional substructure (mcontext_t.regs) containing the volatile
 104   // registers - NIP, among others.
 105   // This substructure may or may not be there depending where uc came from:
 106   // - if uc was handed over as the argument to a sigaction handler, a pointer to the
 107   //   substructure was provided by the kernel when calling the signal handler, and
 108   //   regs->nip can be accessed.
 109   // - if uc was filled by getcontext(), it is undefined - getcontext() does not fill
 110   //   it because the volatile registers are not needed to make setcontext() work.
 111   //   Hopefully it was zero'd out beforehand.
 112   guarantee(uc->uc_mcontext.regs != NULL, "only use ucontext_get_pc in sigaction context");
 113   return (address)uc->uc_mcontext.regs->nip;
 114 }
 115 
 116 // modify PC in ucontext.
 117 // Note: Only use this for an ucontext handed down to a signal handler. See comment
 118 // in ucontext_get_pc.
 119 void os::Linux::ucontext_set_pc(ucontext_t * uc, address pc) {
 120   guarantee(uc->uc_mcontext.regs != NULL, "only use ucontext_set_pc in sigaction context");
 121   uc->uc_mcontext.regs->nip = (unsigned long)pc;
 122 }
 123 
 124 intptr_t* os::Linux::ucontext_get_sp(const ucontext_t * uc) {
 125   return (intptr_t*)uc->uc_mcontext.regs->gpr[1/*REG_SP*/];
 126 }
 127 
 128 intptr_t* os::Linux::ucontext_get_fp(const ucontext_t * uc) {
 129   return NULL;
 130 }
 131 
 132 ExtendedPC os::fetch_frame_from_context(const void* ucVoid,
 133                     intptr_t** ret_sp, intptr_t** ret_fp) {
 134 
 135   ExtendedPC  epc;
 136   const ucontext_t* uc = (const ucontext_t*)ucVoid;
 137 
 138   if (uc != NULL) {
 139     epc = ExtendedPC(os::Linux::ucontext_get_pc(uc));
 140     if (ret_sp) *ret_sp = os::Linux::ucontext_get_sp(uc);
 141     if (ret_fp) *ret_fp = os::Linux::ucontext_get_fp(uc);
 142   } else {
 143     // construct empty ExtendedPC for return value checking
 144     epc = ExtendedPC(NULL);
 145     if (ret_sp) *ret_sp = (intptr_t *)NULL;
 146     if (ret_fp) *ret_fp = (intptr_t *)NULL;
 147   }
 148 
 149   return epc;
 150 }
 151 
 152 frame os::fetch_frame_from_context(const void* ucVoid) {
 153   intptr_t* sp;
 154   intptr_t* fp;
 155   ExtendedPC epc = fetch_frame_from_context(ucVoid, &sp, &fp);
 156   return frame(sp, epc.pc());
 157 }
 158 
 159 bool os::Linux::get_frame_at_stack_banging_point(JavaThread* thread, ucontext_t* uc, frame* fr) {
 160   address pc = (address) os::Linux::ucontext_get_pc(uc);
 161   if (Interpreter::contains(pc)) {
 162     // Interpreter performs stack banging after the fixed frame header has
 163     // been generated while the compilers perform it before. To maintain
 164     // semantic consistency between interpreted and compiled frames, the
 165     // method returns the Java sender of the current frame.
 166     *fr = os::fetch_frame_from_context(uc);
 167     if (!fr->is_first_java_frame()) {
 168       assert(fr->safe_for_sender(thread), "Safety check");
 169       *fr = fr->java_sender();
 170     }
 171   } else {
 172     // More complex code with compiled code.
 173     assert(!Interpreter::contains(pc), "Interpreted methods should have been handled above");
 174     CodeBlob* cb = CodeCache::find_blob(pc);
 175     if (cb == NULL || !cb->is_nmethod() || cb->is_frame_complete_at(pc)) {
 176       // Not sure where the pc points to, fallback to default
 177       // stack overflow handling. In compiled code, we bang before
 178       // the frame is complete.
 179       return false;
 180     } else {
 181       intptr_t* fp = os::Linux::ucontext_get_fp(uc);
 182       intptr_t* sp = os::Linux::ucontext_get_sp(uc);
 183       *fr = frame(sp, (address)*sp);
 184       if (!fr->is_java_frame()) {
 185         assert(fr->safe_for_sender(thread), "Safety check");
 186         assert(!fr->is_first_frame(), "Safety check");
 187         *fr = fr->java_sender();
 188       }
 189     }
 190   }
 191   assert(fr->is_java_frame(), "Safety check");
 192   return true;
 193 }
 194 
 195 frame os::get_sender_for_C_frame(frame* fr) {
 196   if (*fr->sp() == 0) {
 197     // fr is the last C frame
 198     return frame(NULL, NULL);
 199   }
 200   return frame(fr->sender_sp(), fr->sender_pc());
 201 }
 202 
 203 
 204 frame os::current_frame() {
 205   intptr_t* csp = (intptr_t*) *((intptr_t*) os::current_stack_pointer());
 206   // hack.
 207   frame topframe(csp, (address)0x8);
 208   // return sender of current topframe which hopefully has pc != NULL.
 209   return os::get_sender_for_C_frame(&topframe);
 210 }
 211 
 212 // Utility functions
 213 
 214 extern "C" JNIEXPORT int
 215 JVM_handle_linux_signal(int sig,
 216                         siginfo_t* info,
 217                         void* ucVoid,
 218                         int abort_if_unrecognized) {
 219   ucontext_t* uc = (ucontext_t*) ucVoid;
 220 
 221   Thread* t = Thread::current_or_null_safe();
 222 
 223   SignalHandlerMark shm(t);
 224 
 225   // Note: it's not uncommon that JNI code uses signal/sigset to install
 226   // then restore certain signal handler (e.g. to temporarily block SIGPIPE,
 227   // or have a SIGILL handler when detecting CPU type). When that happens,
 228   // JVM_handle_linux_signal() might be invoked with junk info/ucVoid. To
 229   // avoid unnecessary crash when libjsig is not preloaded, try handle signals
 230   // that do not require siginfo/ucontext first.
 231 
 232   if (sig == SIGPIPE) {
 233     if (os::Linux::chained_handler(sig, info, ucVoid)) {
 234       return true;
 235     } else {
 236       // Ignoring SIGPIPE - see bugs 4229104
 237       return true;
 238     }
 239   }
 240 
 241   JavaThread* thread = NULL;
 242   VMThread* vmthread = NULL;
 243   if (os::Linux::signal_handlers_are_installed) {
 244     if (t != NULL) {
 245       if(t->is_Java_thread()) {
 246         thread = (JavaThread*)t;
 247       } else if(t->is_VM_thread()) {
 248         vmthread = (VMThread *)t;
 249       }
 250     }
 251   }
 252 
 253   // Moved SafeFetch32 handling outside thread!=NULL conditional block to make
 254   // it work if no associated JavaThread object exists.
 255   if (uc) {
 256     address const pc = os::Linux::ucontext_get_pc(uc);
 257     if (pc && StubRoutines::is_safefetch_fault(pc)) {
 258       os::Linux::ucontext_set_pc(uc, StubRoutines::continuation_for_safefetch_fault(pc));
 259       return true;
 260     }
 261   }
 262 
 263   // decide if this trap can be handled by a stub
 264   address stub = NULL;
 265   address pc   = NULL;
 266 
 267   //%note os_trap_1
 268   if (info != NULL && uc != NULL && thread != NULL) {
 269     pc = (address) os::Linux::ucontext_get_pc(uc);
 270 
 271     // Handle ALL stack overflow variations here
 272     if (sig == SIGSEGV) {
 273       // Si_addr may not be valid due to a bug in the linux-ppc64 kernel (see
 274       // comment below). Use get_stack_bang_address instead of si_addr.
 275       address addr = ((NativeInstruction*)pc)->get_stack_bang_address(uc);
 276 
 277       // Check if fault address is within thread stack.
 278       if (thread->on_local_stack(addr)) {
 279         // stack overflow
 280         if (thread->in_stack_yellow_reserved_zone(addr)) {
 281           if (thread->thread_state() == _thread_in_Java) {
 282             if (thread->in_stack_reserved_zone(addr)) {
 283               frame fr;
 284               if (os::Linux::get_frame_at_stack_banging_point(thread, uc, &fr)) {
 285                 assert(fr.is_java_frame(), "Must be a Javac frame");
 286                 frame activation =
 287                   SharedRuntime::look_for_reserved_stack_annotated_method(thread, fr);
 288                 if (activation.sp() != NULL) {
 289                   thread->disable_stack_reserved_zone();
 290                   if (activation.is_interpreted_frame()) {
 291                     thread->set_reserved_stack_activation((address)activation.fp());
 292                   } else {
 293                     thread->set_reserved_stack_activation((address)activation.unextended_sp());
 294                   }
 295                   return 1;
 296                 }
 297               }
 298             }
 299             // Throw a stack overflow exception.
 300             // Guard pages will be reenabled while unwinding the stack.
 301             thread->disable_stack_yellow_reserved_zone();
 302             stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::STACK_OVERFLOW);
 303           } else {
 304             // Thread was in the vm or native code. Return and try to finish.
 305             thread->disable_stack_yellow_reserved_zone();
 306             return 1;
 307           }
 308         } else if (thread->in_stack_red_zone(addr)) {
 309           // Fatal red zone violation.  Disable the guard pages and fall through
 310           // to handle_unexpected_exception way down below.
 311           thread->disable_stack_red_zone();
 312           tty->print_raw_cr("An irrecoverable stack overflow has occurred.");
 313 
 314           // This is a likely cause, but hard to verify. Let's just print
 315           // it as a hint.
 316           tty->print_raw_cr("Please check if any of your loaded .so files has "
 317                             "enabled executable stack (see man page execstack(8))");
 318         } else {
 319           // Accessing stack address below sp may cause SEGV if current
 320           // thread has MAP_GROWSDOWN stack. This should only happen when
 321           // current thread was created by user code with MAP_GROWSDOWN flag
 322           // and then attached to VM. See notes in os_linux.cpp.
 323           if (thread->osthread()->expanding_stack() == 0) {
 324              thread->osthread()->set_expanding_stack();
 325              if (os::Linux::manually_expand_stack(thread, addr)) {
 326                thread->osthread()->clear_expanding_stack();
 327                return 1;
 328              }
 329              thread->osthread()->clear_expanding_stack();
 330           } else {
 331              fatal("recursive segv. expanding stack.");
 332           }
 333         }
 334       }
 335     }
 336 
 337     if (thread->thread_state() == _thread_in_Java) {
 338       // Java thread running in Java code => find exception handler if any
 339       // a fault inside compiled code, the interpreter, or a stub
 340 
 341       // A VM-related SIGILL may only occur if we are not in the zero page.
 342       // On AIX, we get a SIGILL if we jump to 0x0 or to somewhere else
 343       // in the zero page, because it is filled with 0x0. We ignore
 344       // explicit SIGILLs in the zero page.
 345       if (sig == SIGILL && (pc < (address) 0x200)) {
 346         if (TraceTraps) {
 347           tty->print_raw_cr("SIGILL happened inside zero page.");
 348         }
 349         goto report_and_die;
 350       }
 351 
 352       CodeBlob *cb = NULL;
 353       // Handle signal from NativeJump::patch_verified_entry().
 354       if (( TrapBasedNotEntrantChecks && sig == SIGTRAP && nativeInstruction_at(pc)->is_sigtrap_zombie_not_entrant()) ||
 355           (!TrapBasedNotEntrantChecks && sig == SIGILL  && nativeInstruction_at(pc)->is_sigill_zombie_not_entrant())) {
 356         if (TraceTraps) {
 357           tty->print_cr("trap: zombie_not_entrant (%s)", (sig == SIGTRAP) ? "SIGTRAP" : "SIGILL");
 358         }
 359         stub = SharedRuntime::get_handle_wrong_method_stub();
 360       }
 361 
 362       else if (sig == SIGSEGV &&
 363                // A linux-ppc64 kernel before 2.6.6 doesn't set si_addr on some segfaults
 364                // in 64bit mode (cf. http://www.kernel.org/pub/linux/kernel/v2.6/ChangeLog-2.6.6),
 365                // especially when we try to read from the safepoint polling page. So the check
 366                //   (address)info->si_addr == os::get_standard_polling_page()
 367                // doesn't work for us. We use:
 368                ((NativeInstruction*)pc)->is_safepoint_poll() &&
 369                CodeCache::contains((void*) pc) &&
 370                ((cb = CodeCache::find_blob(pc)) != NULL) &&
 371                cb->is_compiled()) {
 372         if (TraceTraps) {
 373           tty->print_cr("trap: safepoint_poll at " INTPTR_FORMAT " (SIGSEGV)", p2i(pc));
 374         }
 375         stub = SharedRuntime::get_poll_stub(pc);
 376       }
 377 
 378       // SIGTRAP-based ic miss check in compiled code.
 379       else if (sig == SIGTRAP && TrapBasedICMissChecks &&
 380                nativeInstruction_at(pc)->is_sigtrap_ic_miss_check()) {
 381         if (TraceTraps) {
 382           tty->print_cr("trap: ic_miss_check at " INTPTR_FORMAT " (SIGTRAP)", p2i(pc));
 383         }
 384         stub = SharedRuntime::get_ic_miss_stub();
 385       }
 386 
 387       // SIGTRAP-based implicit null check in compiled code.
 388       else if (sig == SIGTRAP && TrapBasedNullChecks &&
 389                nativeInstruction_at(pc)->is_sigtrap_null_check()) {
 390         if (TraceTraps) {
 391           tty->print_cr("trap: null_check at " INTPTR_FORMAT " (SIGTRAP)", p2i(pc));
 392         }
 393         stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_NULL);
 394       }
 395 
 396       // SIGSEGV-based implicit null check in compiled code.
 397       else if (sig == SIGSEGV && ImplicitNullChecks &&
 398                CodeCache::contains((void*) pc) &&
 399                !MacroAssembler::needs_explicit_null_check((intptr_t) info->si_addr)) {
 400         if (TraceTraps) {
 401           tty->print_cr("trap: null_check at " INTPTR_FORMAT " (SIGSEGV)", p2i(pc));
 402         }
 403         stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_NULL);
 404       }
 405 
 406 #ifdef COMPILER2
 407       // SIGTRAP-based implicit range check in compiled code.
 408       else if (sig == SIGTRAP && TrapBasedRangeChecks &&
 409                nativeInstruction_at(pc)->is_sigtrap_range_check()) {
 410         if (TraceTraps) {
 411           tty->print_cr("trap: range_check at " INTPTR_FORMAT " (SIGTRAP)", p2i(pc));
 412         }
 413         stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_NULL);
 414       }
 415 #endif
 416       else if (sig == SIGBUS) {
 417         // BugId 4454115: A read from a MappedByteBuffer can fault here if the
 418         // underlying file has been truncated. Do not crash the VM in such a case.
 419         CodeBlob* cb = CodeCache::find_blob_unsafe(pc);
 420         CompiledMethod* nm = (cb != NULL) ? cb->as_compiled_method_or_null() : NULL;
 421         if (nm != NULL && nm->has_unsafe_access()) {
 422           address next_pc = pc + 4;
 423           next_pc = SharedRuntime::handle_unsafe_access(thread, next_pc);
 424           os::Linux::ucontext_set_pc(uc, next_pc);
 425           return true;
 426         }
 427       }
 428     }
 429 
 430     else { // thread->thread_state() != _thread_in_Java
 431       if (sig == SIGILL && VM_Version::is_determine_features_test_running()) {
 432         // SIGILL must be caused by VM_Version::determine_features().
 433         *(int *)pc = 0; // patch instruction to 0 to indicate that it causes a SIGILL,
 434                         // flushing of icache is not necessary.
 435         stub = pc + 4;  // continue with next instruction.
 436       }
 437       else if (thread->thread_state() == _thread_in_vm &&
 438                sig == SIGBUS && thread->doing_unsafe_access()) {
 439         address next_pc = pc + 4;
 440         next_pc = SharedRuntime::handle_unsafe_access(thread, next_pc);
 441         os::Linux::ucontext_set_pc(uc, pc + 4);
 442         return true;
 443       }
 444     }
 445 
 446     // Check to see if we caught the safepoint code in the
 447     // process of write protecting the memory serialization page.
 448     // It write enables the page immediately after protecting it
 449     // so we can just return to retry the write.
 450     if ((sig == SIGSEGV) &&
 451         // Si_addr may not be valid due to a bug in the linux-ppc64 kernel (see comment above).
 452         // Use is_memory_serialization instead of si_addr.
 453         ((NativeInstruction*)pc)->is_memory_serialization(thread, ucVoid)) {
 454       // Synchronization problem in the pseudo memory barrier code (bug id 6546278)
 455       // Block current thread until the memory serialize page permission restored.
 456       os::block_on_serialize_page_trap();
 457       return true;
 458     }
 459   }
 460 
 461   if (stub != NULL) {
 462     // Save all thread context in case we need to restore it.
 463     if (thread != NULL) thread->set_saved_exception_pc(pc);
 464     os::Linux::ucontext_set_pc(uc, stub);
 465     return true;
 466   }
 467 
 468   // signal-chaining
 469   if (os::Linux::chained_handler(sig, info, ucVoid)) {
 470     return true;
 471   }
 472 
 473   if (!abort_if_unrecognized) {
 474     // caller wants another chance, so give it to him
 475     return false;
 476   }
 477 
 478   if (pc == NULL && uc != NULL) {
 479     pc = os::Linux::ucontext_get_pc(uc);
 480   }
 481 
 482 report_and_die:
 483   // unmask current signal
 484   sigset_t newset;
 485   sigemptyset(&newset);
 486   sigaddset(&newset, sig);
 487   sigprocmask(SIG_UNBLOCK, &newset, NULL);
 488 
 489   VMError::report_and_die(t, sig, pc, info, ucVoid);
 490 
 491   ShouldNotReachHere();
 492   return false;
 493 }
 494 
 495 void os::Linux::init_thread_fpu_state(void) {
 496   // Disable FP exceptions.
 497   __asm__ __volatile__ ("mtfsfi 6,0");
 498 }
 499 
 500 int os::Linux::get_fpu_control_word(void) {
 501   // x86 has problems with FPU precision after pthread_cond_timedwait().
 502   // nothing to do on ppc64.
 503   return 0;
 504 }
 505 
 506 void os::Linux::set_fpu_control_word(int fpu_control) {
 507   // x86 has problems with FPU precision after pthread_cond_timedwait().
 508   // nothing to do on ppc64.
 509 }
 510 
 511 ////////////////////////////////////////////////////////////////////////////////
 512 // thread stack
 513 
 514 size_t os::Linux::min_stack_allowed = 128*K;
 515 
 516 // return default stack size for thr_type
 517 size_t os::Linux::default_stack_size(os::ThreadType thr_type) {
 518   // default stack size (compiler thread needs larger stack)
 519   // Notice that the setting for compiler threads here have no impact
 520   // because of the strange 'fallback logic' in os::create_thread().
 521   // Better set CompilerThreadStackSize in globals_<os_cpu>.hpp if you want to
 522   // specify a different stack size for compiler threads!
 523   size_t s = (thr_type == os::compiler_thread ? 4 * M : 1024 * K);
 524   return s;
 525 }
 526 
 527 size_t os::Linux::default_guard_size(os::ThreadType thr_type) {
 528   return 2 * page_size();
 529 }
 530 
 531 // Java thread:
 532 //
 533 //   Low memory addresses
 534 //    +------------------------+
 535 //    |                        |\  JavaThread created by VM does not have glibc
 536 //    |    glibc guard page    | - guard, attached Java thread usually has
 537 //    |                        |/  1 page glibc guard.
 538 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()
 539 //    |                        |\
 540 //    |  HotSpot Guard Pages   | - red and yellow pages
 541 //    |                        |/
 542 //    +------------------------+ JavaThread::stack_yellow_zone_base()
 543 //    |                        |\
 544 //    |      Normal Stack      | -
 545 //    |                        |/
 546 // P2 +------------------------+ Thread::stack_base()
 547 //
 548 // Non-Java thread:
 549 //
 550 //   Low memory addresses
 551 //    +------------------------+
 552 //    |                        |\
 553 //    |  glibc guard page      | - usually 1 page
 554 //    |                        |/
 555 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()
 556 //    |                        |\
 557 //    |      Normal Stack      | -
 558 //    |                        |/
 559 // P2 +------------------------+ Thread::stack_base()
 560 //
 561 // ** P1 (aka bottom) and size ( P2 = P1 - size) are the address and stack size returned from
 562 //    pthread_attr_getstack()
 563 
 564 static void current_stack_region(address * bottom, size_t * size) {
 565   if (os::Linux::is_initial_thread()) {
 566      // initial thread needs special handling because pthread_getattr_np()
 567      // may return bogus value.
 568     *bottom = os::Linux::initial_thread_stack_bottom();
 569     *size   = os::Linux::initial_thread_stack_size();
 570   } else {
 571     pthread_attr_t attr;
 572 
 573     int rslt = pthread_getattr_np(pthread_self(), &attr);
 574 
 575     // JVM needs to know exact stack location, abort if it fails
 576     if (rslt != 0) {
 577       if (rslt == ENOMEM) {
 578         vm_exit_out_of_memory(0, OOM_MMAP_ERROR, "pthread_getattr_np");
 579       } else {
 580         fatal("pthread_getattr_np failed with errno = %d", rslt);
 581       }
 582     }
 583 
 584     if (pthread_attr_getstack(&attr, (void **)bottom, size) != 0) {
 585       fatal("Can not locate current stack attributes!");
 586     }
 587 
 588     pthread_attr_destroy(&attr);
 589 
 590   }
 591   assert(os::current_stack_pointer() >= *bottom &&
 592          os::current_stack_pointer() < *bottom + *size, "just checking");
 593 }
 594 
 595 address os::current_stack_base() {
 596   address bottom;
 597   size_t size;
 598   current_stack_region(&bottom, &size);
 599   return (bottom + size);
 600 }
 601 
 602 size_t os::current_stack_size() {
 603   // stack size includes normal stack and HotSpot guard pages
 604   address bottom;
 605   size_t size;
 606   current_stack_region(&bottom, &size);
 607   return size;
 608 }
 609 
 610 /////////////////////////////////////////////////////////////////////////////
 611 // helper functions for fatal error handler
 612 
 613 void os::print_context(outputStream *st, const void *context) {
 614   if (context == NULL) return;
 615 
 616   const ucontext_t* uc = (const ucontext_t*)context;
 617 
 618   st->print_cr("Registers:");
 619   st->print("pc =" INTPTR_FORMAT "  ", uc->uc_mcontext.regs->nip);
 620   st->print("lr =" INTPTR_FORMAT "  ", uc->uc_mcontext.regs->link);
 621   st->print("ctr=" INTPTR_FORMAT "  ", uc->uc_mcontext.regs->ctr);
 622   st->cr();
 623   for (int i = 0; i < 32; i++) {
 624     st->print("r%-2d=" INTPTR_FORMAT "  ", i, uc->uc_mcontext.regs->gpr[i]);
 625     if (i % 3 == 2) st->cr();
 626   }
 627   st->cr();
 628   st->cr();
 629 
 630   intptr_t *sp = (intptr_t *)os::Linux::ucontext_get_sp(uc);
 631   st->print_cr("Top of Stack: (sp=" PTR_FORMAT ")", p2i(sp));
 632   print_hex_dump(st, (address)sp, (address)(sp + 128), sizeof(intptr_t));
 633   st->cr();
 634 
 635   // Note: it may be unsafe to inspect memory near pc. For example, pc may
 636   // point to garbage if entry point in an nmethod is corrupted. Leave
 637   // this at the end, and hope for the best.
 638   address pc = os::Linux::ucontext_get_pc(uc);
 639   st->print_cr("Instructions: (pc=" PTR_FORMAT ")", p2i(pc));
 640   print_hex_dump(st, pc - 64, pc + 64, /*instrsize=*/4);
 641   st->cr();
 642 }
 643 
 644 void os::print_register_info(outputStream *st, const void *context) {
 645   if (context == NULL) return;
 646 
 647   const ucontext_t *uc = (const ucontext_t*)context;
 648 
 649   st->print_cr("Register to memory mapping:");
 650   st->cr();
 651 
 652   // this is only for the "general purpose" registers
 653   for (int i = 0; i < 32; i++) {
 654     st->print("r%-2d=", i);
 655     print_location(st, uc->uc_mcontext.regs->gpr[i]);
 656   }
 657   st->cr();
 658 }
 659 
 660 extern "C" {
 661   int SpinPause() {
 662     return 0;
 663   }
 664 }
 665 
 666 #ifndef PRODUCT
 667 void os::verify_stack_alignment() {
 668   assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment");
 669 }
 670 #endif
 671 
 672 int os::extra_bang_size_in_bytes() {
 673   // PPC does not require the additional stack bang.
 674   return 0;
 675 }