1 /*
   2  * Copyright (c) 1999, 2016, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
  22  *
  23  */
  24 
  25 // no precompiled headers
  26 #include "asm/macroAssembler.hpp"
  27 #include "classfile/classLoader.hpp"
  28 #include "classfile/systemDictionary.hpp"
  29 #include "classfile/vmSymbols.hpp"
  30 #include "code/codeCache.hpp"
  31 #include "code/icBuffer.hpp"
  32 #include "code/vtableStubs.hpp"
  33 #include "interpreter/interpreter.hpp"
  34 #include "jvm_linux.h"
  35 #include "memory/allocation.inline.hpp"
  36 #include "mutex_linux.inline.hpp"
  37 #include "os_share_linux.hpp"
  38 #include "prims/jniFastGetField.hpp"
  39 #include "prims/jvm.h"
  40 #include "prims/jvm_misc.hpp"
  41 #include "runtime/arguments.hpp"
  42 #include "runtime/extendedPC.hpp"
  43 #include "runtime/frame.inline.hpp"
  44 #include "runtime/interfaceSupport.hpp"
  45 #include "runtime/java.hpp"
  46 #include "runtime/javaCalls.hpp"
  47 #include "runtime/mutexLocker.hpp"
  48 #include "runtime/osThread.hpp"
  49 #include "runtime/sharedRuntime.hpp"
  50 #include "runtime/stubRoutines.hpp"
  51 #include "runtime/thread.inline.hpp"
  52 #include "runtime/timer.hpp"
  53 #include "services/memTracker.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 # include <fpu_control.h>
  78 
  79 #ifdef AMD64
  80 #define REG_SP REG_RSP
  81 #define REG_PC REG_RIP
  82 #define REG_FP REG_RBP
  83 #define SPELL_REG_SP "rsp"
  84 #define SPELL_REG_FP "rbp"
  85 #else
  86 #define REG_SP REG_UESP
  87 #define REG_PC REG_EIP
  88 #define REG_FP REG_EBP
  89 #define SPELL_REG_SP "esp"
  90 #define SPELL_REG_FP "ebp"
  91 #endif // AMD64
  92 
  93 address os::current_stack_pointer() {
  94 #ifdef SPARC_WORKS
  95   register void *esp;
  96   __asm__("mov %%"SPELL_REG_SP", %0":"=r"(esp));
  97   return (address) ((char*)esp + sizeof(long)*2);
  98 #elif defined(__clang__)
  99   intptr_t* esp;
 100   __asm__ __volatile__ ("mov %%"SPELL_REG_SP", %0":"=r"(esp):);
 101   return (address) esp;
 102 #else
 103   register void *esp __asm__ (SPELL_REG_SP);
 104   return (address) esp;
 105 #endif
 106 }
 107 
 108 char* os::non_memory_address_word() {
 109   // Must never look like an address returned by reserve_memory,
 110   // even in its subfields (as defined by the CPU immediate fields,
 111   // if the CPU splits constants across multiple instructions).
 112 
 113   return (char*) -1;
 114 }
 115 
 116 void os::initialize_thread(Thread* thr) {
 117 // Nothing to do.
 118 }
 119 
 120 address os::Linux::ucontext_get_pc(const ucontext_t * uc) {
 121   return (address)uc->uc_mcontext.gregs[REG_PC];
 122 }
 123 
 124 void os::Linux::ucontext_set_pc(ucontext_t * uc, address pc) {
 125   uc->uc_mcontext.gregs[REG_PC] = (intptr_t)pc;
 126 }
 127 
 128 intptr_t* os::Linux::ucontext_get_sp(const ucontext_t * uc) {
 129   return (intptr_t*)uc->uc_mcontext.gregs[REG_SP];
 130 }
 131 
 132 intptr_t* os::Linux::ucontext_get_fp(const ucontext_t * uc) {
 133   return (intptr_t*)uc->uc_mcontext.gregs[REG_FP];
 134 }
 135 
 136 // For Forte Analyzer AsyncGetCallTrace profiling support - thread
 137 // is currently interrupted by SIGPROF.
 138 // os::Solaris::fetch_frame_from_ucontext() tries to skip nested signal
 139 // frames. Currently we don't do that on Linux, so it's the same as
 140 // os::fetch_frame_from_context().
 141 // This method is also used for stack overflow signal handling.
 142 ExtendedPC os::Linux::fetch_frame_from_ucontext(Thread* thread,
 143   const ucontext_t* uc, intptr_t** ret_sp, intptr_t** ret_fp) {
 144 
 145   assert(thread != NULL, "just checking");
 146   assert(ret_sp != NULL, "just checking");
 147   assert(ret_fp != NULL, "just checking");
 148 
 149   return os::fetch_frame_from_context(uc, ret_sp, ret_fp);
 150 }
 151 
 152 ExtendedPC os::fetch_frame_from_context(const void* ucVoid,
 153                     intptr_t** ret_sp, intptr_t** ret_fp) {
 154 
 155   ExtendedPC  epc;
 156   const ucontext_t* uc = (const ucontext_t*)ucVoid;
 157 
 158   if (uc != NULL) {
 159     epc = ExtendedPC(os::Linux::ucontext_get_pc(uc));
 160     if (ret_sp) *ret_sp = os::Linux::ucontext_get_sp(uc);
 161     if (ret_fp) *ret_fp = os::Linux::ucontext_get_fp(uc);
 162   } else {
 163     // construct empty ExtendedPC for return value checking
 164     epc = ExtendedPC(NULL);
 165     if (ret_sp) *ret_sp = (intptr_t *)NULL;
 166     if (ret_fp) *ret_fp = (intptr_t *)NULL;
 167   }
 168 
 169   return epc;
 170 }
 171 
 172 frame os::fetch_frame_from_context(const void* ucVoid) {
 173   intptr_t* sp;
 174   intptr_t* fp;
 175   ExtendedPC epc = fetch_frame_from_context(ucVoid, &sp, &fp);
 176   return frame(sp, fp, epc.pc());
 177 }
 178 
 179 frame os::fetch_frame_from_ucontext(Thread* thread, void* ucVoid) {
 180   intptr_t* sp;
 181   intptr_t* fp;
 182   ExtendedPC epc = os::Linux::fetch_frame_from_ucontext(thread, (ucontext_t*)ucVoid, &sp, &fp);
 183   return frame(sp, fp, epc.pc());
 184 }
 185 
 186 bool os::Linux::get_frame_at_stack_banging_point(JavaThread* thread, ucontext_t* uc, frame* fr) {
 187   address pc = (address) os::Linux::ucontext_get_pc(uc);
 188   if (Interpreter::contains(pc)) {
 189     // interpreter performs stack banging after the fixed frame header has
 190     // been generated while the compilers perform it before. To maintain
 191     // semantic consistency between interpreted and compiled frames, the
 192     // method returns the Java sender of the current frame.
 193     *fr = os::fetch_frame_from_ucontext(thread, uc);
 194     if (!fr->is_first_java_frame()) {
 195       assert(fr->safe_for_sender(thread), "Safety check");
 196       *fr = fr->java_sender();
 197     }
 198   } else {
 199     // more complex code with compiled code
 200     assert(!Interpreter::contains(pc), "Interpreted methods should have been handled above");
 201     CodeBlob* cb = CodeCache::find_blob(pc);
 202     if (cb == NULL || !cb->is_nmethod() || cb->is_frame_complete_at(pc)) {
 203       // Not sure where the pc points to, fallback to default
 204       // stack overflow handling
 205       return false;
 206     } else {
 207       // in compiled code, the stack banging is performed just after the return pc
 208       // has been pushed on the stack
 209       intptr_t* fp = os::Linux::ucontext_get_fp(uc);
 210       intptr_t* sp = os::Linux::ucontext_get_sp(uc);
 211       *fr = frame(sp + 1, fp, (address)*sp);
 212       if (!fr->is_java_frame()) {
 213         assert(fr->safe_for_sender(thread), "Safety check");
 214         assert(!fr->is_first_frame(), "Safety check");
 215         *fr = fr->java_sender();
 216       }
 217     }
 218   }
 219   assert(fr->is_java_frame(), "Safety check");
 220   return true;
 221 }
 222 
 223 // By default, gcc always save frame pointer (%ebp/%rbp) on stack. It may get
 224 // turned off by -fomit-frame-pointer,
 225 frame os::get_sender_for_C_frame(frame* fr) {
 226   return frame(fr->sender_sp(), fr->link(), fr->sender_pc());
 227 }
 228 
 229 intptr_t* _get_previous_fp() {
 230 #ifdef SPARC_WORKS
 231   register intptr_t **ebp;
 232   __asm__("mov %%"SPELL_REG_FP", %0":"=r"(ebp));
 233 #elif defined(__clang__)
 234   intptr_t **ebp;
 235   __asm__ __volatile__ ("mov %%"SPELL_REG_FP", %0":"=r"(ebp):);
 236 #else
 237   register intptr_t **ebp __asm__ (SPELL_REG_FP);
 238 #endif
 239   return (intptr_t*) *ebp;   // we want what it points to.
 240 }
 241 
 242 
 243 frame os::current_frame() {
 244   intptr_t* fp = _get_previous_fp();
 245   frame myframe((intptr_t*)os::current_stack_pointer(),
 246                 (intptr_t*)fp,
 247                 CAST_FROM_FN_PTR(address, os::current_frame));
 248   if (os::is_first_C_frame(&myframe)) {
 249     // stack is not walkable
 250     return frame();
 251   } else {
 252     return os::get_sender_for_C_frame(&myframe);
 253   }
 254 }
 255 
 256 // Utility functions
 257 
 258 // From IA32 System Programming Guide
 259 enum {
 260   trap_page_fault = 0xE
 261 };
 262 
 263 extern "C" JNIEXPORT int
 264 JVM_handle_linux_signal(int sig,
 265                         siginfo_t* info,
 266                         void* ucVoid,
 267                         int abort_if_unrecognized) {
 268   ucontext_t* uc = (ucontext_t*) ucVoid;
 269 
 270   Thread* t = Thread::current_or_null_safe();
 271 
 272   // Must do this before SignalHandlerMark, if crash protection installed we will longjmp away
 273   // (no destructors can be run)
 274   os::WatcherThreadCrashProtection::check_crash_protection(sig, t);
 275 
 276   SignalHandlerMark shm(t);
 277 
 278   // Note: it's not uncommon that JNI code uses signal/sigset to install
 279   // then restore certain signal handler (e.g. to temporarily block SIGPIPE,
 280   // or have a SIGILL handler when detecting CPU type). When that happens,
 281   // JVM_handle_linux_signal() might be invoked with junk info/ucVoid. To
 282   // avoid unnecessary crash when libjsig is not preloaded, try handle signals
 283   // that do not require siginfo/ucontext first.
 284 
 285   if (sig == SIGPIPE || sig == SIGXFSZ) {
 286     // allow chained handler to go first
 287     if (os::Linux::chained_handler(sig, info, ucVoid)) {
 288       return true;
 289     } else {
 290       // Ignoring SIGPIPE/SIGXFSZ - see bugs 4229104 or 6499219
 291       return true;
 292     }
 293   }
 294 
 295   JavaThread* thread = NULL;
 296   VMThread* vmthread = NULL;
 297   if (os::Linux::signal_handlers_are_installed) {
 298     if (t != NULL ){
 299       if(t->is_Java_thread()) {
 300         thread = (JavaThread*)t;
 301       }
 302       else if(t->is_VM_thread()){
 303         vmthread = (VMThread *)t;
 304       }
 305     }
 306   }
 307 /*
 308   NOTE: does not seem to work on linux.
 309   if (info == NULL || info->si_code <= 0 || info->si_code == SI_NOINFO) {
 310     // can't decode this kind of signal
 311     info = NULL;
 312   } else {
 313     assert(sig == info->si_signo, "bad siginfo");
 314   }
 315 */
 316   // decide if this trap can be handled by a stub
 317   address stub = NULL;
 318 
 319   address pc          = NULL;
 320 
 321   //%note os_trap_1
 322   if (info != NULL && uc != NULL && thread != NULL) {
 323     pc = (address) os::Linux::ucontext_get_pc(uc);
 324 
 325     if (StubRoutines::is_safefetch_fault(pc)) {
 326       os::Linux::ucontext_set_pc(uc, StubRoutines::continuation_for_safefetch_fault(pc));
 327       return 1;
 328     }
 329 
 330 #ifndef AMD64
 331     // Halt if SI_KERNEL before more crashes get misdiagnosed as Java bugs
 332     // This can happen in any running code (currently more frequently in
 333     // interpreter code but has been seen in compiled code)
 334     if (sig == SIGSEGV && info->si_addr == 0 && info->si_code == SI_KERNEL) {
 335       fatal("An irrecoverable SI_KERNEL SIGSEGV has occurred due "
 336             "to unstable signal handling in this distribution.");
 337     }
 338 #endif // AMD64
 339 
 340     // Handle ALL stack overflow variations here
 341     if (sig == SIGSEGV) {
 342       address addr = (address) info->si_addr;
 343 
 344       // check if fault address is within thread stack
 345       if (thread->on_local_stack(addr)) {
 346         // stack overflow
 347         if (thread->in_stack_yellow_reserved_zone(addr)) {
 348           if (thread->thread_state() == _thread_in_Java) {
 349             if (thread->in_stack_reserved_zone(addr)) {
 350               frame fr;
 351               if (os::Linux::get_frame_at_stack_banging_point(thread, uc, &fr)) {
 352                 assert(fr.is_java_frame(), "Must be a Java frame");
 353                 frame activation =
 354                   SharedRuntime::look_for_reserved_stack_annotated_method(thread, fr);
 355                 if (activation.sp() != NULL) {
 356                   thread->disable_stack_reserved_zone();
 357                   if (activation.is_interpreted_frame()) {
 358                     thread->set_reserved_stack_activation((address)(
 359                       activation.fp() + frame::interpreter_frame_initial_sp_offset));
 360                   } else {
 361                     thread->set_reserved_stack_activation((address)activation.unextended_sp());
 362                   }
 363                   return 1;
 364                 }
 365               }
 366             }
 367             // Throw a stack overflow exception.  Guard pages will be reenabled
 368             // while unwinding the stack.
 369             thread->disable_stack_yellow_reserved_zone();
 370             stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::STACK_OVERFLOW);
 371           } else {
 372             // Thread was in the vm or native code.  Return and try to finish.
 373             thread->disable_stack_yellow_reserved_zone();
 374             return 1;
 375           }
 376         } else if (thread->in_stack_red_zone(addr)) {
 377           // Fatal red zone violation.  Disable the guard pages and fall through
 378           // to handle_unexpected_exception way down below.
 379           thread->disable_stack_red_zone();
 380           tty->print_raw_cr("An irrecoverable stack overflow has occurred.");
 381 
 382           // This is a likely cause, but hard to verify. Let's just print
 383           // it as a hint.
 384           tty->print_raw_cr("Please check if any of your loaded .so files has "
 385                             "enabled executable stack (see man page execstack(8))");
 386         } else {
 387           // Accessing stack address below sp may cause SEGV if current
 388           // thread has MAP_GROWSDOWN stack. This should only happen when
 389           // current thread was created by user code with MAP_GROWSDOWN flag
 390           // and then attached to VM. See notes in os_linux.cpp.
 391           if (thread->osthread()->expanding_stack() == 0) {
 392              thread->osthread()->set_expanding_stack();
 393              if (os::Linux::manually_expand_stack(thread, addr)) {
 394                thread->osthread()->clear_expanding_stack();
 395                return 1;
 396              }
 397              thread->osthread()->clear_expanding_stack();
 398           } else {
 399              fatal("recursive segv. expanding stack.");
 400           }
 401         }
 402       }
 403     }
 404 
 405     if ((sig == SIGSEGV) && VM_Version::is_cpuinfo_segv_addr(pc)) {
 406       // Verify that OS save/restore AVX registers.
 407       stub = VM_Version::cpuinfo_cont_addr();
 408     }
 409 
 410     if (thread->thread_state() == _thread_in_Java) {
 411       // Java thread running in Java code => find exception handler if any
 412       // a fault inside compiled code, the interpreter, or a stub
 413 
 414       if (sig == SIGSEGV && os::is_poll_address((address)info->si_addr)) {
 415         stub = SharedRuntime::get_poll_stub(pc);
 416       } else if (sig == SIGBUS /* && info->si_code == BUS_OBJERR */) {
 417         // BugId 4454115: A read from a MappedByteBuffer can fault
 418         // here if the underlying file has been truncated.
 419         // Do not crash the VM in such a case.
 420         CodeBlob* cb = CodeCache::find_blob_unsafe(pc);
 421         CompiledMethod* nm = (cb != NULL) ? cb->as_compiled_method_or_null() : NULL;
 422         if (nm != NULL && nm->has_unsafe_access()) {
 423           address next_pc = Assembler::locate_next_instruction(pc);
 424           stub = SharedRuntime::handle_unsafe_access(thread, next_pc);
 425         }
 426       }
 427       else
 428 
 429 #ifdef AMD64
 430       if (sig == SIGFPE  &&
 431           (info->si_code == FPE_INTDIV || info->si_code == FPE_FLTDIV)) {
 432         stub =
 433           SharedRuntime::
 434           continuation_for_implicit_exception(thread,
 435                                               pc,
 436                                               SharedRuntime::
 437                                               IMPLICIT_DIVIDE_BY_ZERO);
 438 #else
 439       if (sig == SIGFPE /* && info->si_code == FPE_INTDIV */) {
 440         // HACK: si_code does not work on linux 2.2.12-20!!!
 441         int op = pc[0];
 442         if (op == 0xDB) {
 443           // FIST
 444           // TODO: The encoding of D2I in i486.ad can cause an exception
 445           // prior to the fist instruction if there was an invalid operation
 446           // pending. We want to dismiss that exception. From the win_32
 447           // side it also seems that if it really was the fist causing
 448           // the exception that we do the d2i by hand with different
 449           // rounding. Seems kind of weird.
 450           // NOTE: that we take the exception at the NEXT floating point instruction.
 451           assert(pc[0] == 0xDB, "not a FIST opcode");
 452           assert(pc[1] == 0x14, "not a FIST opcode");
 453           assert(pc[2] == 0x24, "not a FIST opcode");
 454           return true;
 455         } else if (op == 0xF7) {
 456           // IDIV
 457           stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_DIVIDE_BY_ZERO);
 458         } else {
 459           // TODO: handle more cases if we are using other x86 instructions
 460           //   that can generate SIGFPE signal on linux.
 461           tty->print_cr("unknown opcode 0x%X with SIGFPE.", op);
 462           fatal("please update this code.");
 463         }
 464 #endif // AMD64
 465       } else if (sig == SIGSEGV &&
 466                !MacroAssembler::needs_explicit_null_check((intptr_t)info->si_addr)) {
 467           // Determination of interpreter/vtable stub/compiled code null exception
 468           stub = SharedRuntime::continuation_for_implicit_exception(thread, pc, SharedRuntime::IMPLICIT_NULL);
 469       }
 470     } else if (thread->thread_state() == _thread_in_vm &&
 471                sig == SIGBUS && /* info->si_code == BUS_OBJERR && */
 472                thread->doing_unsafe_access()) {
 473         address next_pc = Assembler::locate_next_instruction(pc);
 474         stub = SharedRuntime::handle_unsafe_access(thread, next_pc);
 475     }
 476 
 477     // jni_fast_Get<Primitive>Field can trap at certain pc's if a GC kicks in
 478     // and the heap gets shrunk before the field access.
 479     if ((sig == SIGSEGV) || (sig == SIGBUS)) {
 480       address addr = JNI_FastGetField::find_slowcase_pc(pc);
 481       if (addr != (address)-1) {
 482         stub = addr;
 483       }
 484     }
 485 
 486     // Check to see if we caught the safepoint code in the
 487     // process of write protecting the memory serialization page.
 488     // It write enables the page immediately after protecting it
 489     // so we can just return to retry the write.
 490     if ((sig == SIGSEGV) &&
 491         os::is_memory_serialize_page(thread, (address) info->si_addr)) {
 492       // Block current thread until the memory serialize page permission restored.
 493       os::block_on_serialize_page_trap();
 494       return true;
 495     }
 496   }
 497 
 498 #ifndef AMD64
 499   // Execution protection violation
 500   //
 501   // This should be kept as the last step in the triage.  We don't
 502   // have a dedicated trap number for a no-execute fault, so be
 503   // conservative and allow other handlers the first shot.
 504   //
 505   // Note: We don't test that info->si_code == SEGV_ACCERR here.
 506   // this si_code is so generic that it is almost meaningless; and
 507   // the si_code for this condition may change in the future.
 508   // Furthermore, a false-positive should be harmless.
 509   if (UnguardOnExecutionViolation > 0 &&
 510       (sig == SIGSEGV || sig == SIGBUS) &&
 511       uc->uc_mcontext.gregs[REG_TRAPNO] == trap_page_fault) {
 512     int page_size = os::vm_page_size();
 513     address addr = (address) info->si_addr;
 514     address pc = os::Linux::ucontext_get_pc(uc);
 515     // Make sure the pc and the faulting address are sane.
 516     //
 517     // If an instruction spans a page boundary, and the page containing
 518     // the beginning of the instruction is executable but the following
 519     // page is not, the pc and the faulting address might be slightly
 520     // different - we still want to unguard the 2nd page in this case.
 521     //
 522     // 15 bytes seems to be a (very) safe value for max instruction size.
 523     bool pc_is_near_addr =
 524       (pointer_delta((void*) addr, (void*) pc, sizeof(char)) < 15);
 525     bool instr_spans_page_boundary =
 526       (align_size_down((intptr_t) pc ^ (intptr_t) addr,
 527                        (intptr_t) page_size) > 0);
 528 
 529     if (pc == addr || (pc_is_near_addr && instr_spans_page_boundary)) {
 530       static volatile address last_addr =
 531         (address) os::non_memory_address_word();
 532 
 533       // In conservative mode, don't unguard unless the address is in the VM
 534       if (addr != last_addr &&
 535           (UnguardOnExecutionViolation > 1 || os::address_is_in_vm(addr))) {
 536 
 537         // Set memory to RWX and retry
 538         address page_start =
 539           (address) align_size_down((intptr_t) addr, (intptr_t) page_size);
 540         bool res = os::protect_memory((char*) page_start, page_size,
 541                                       os::MEM_PROT_RWX);
 542 
 543         log_debug(os)("Execution protection violation "
 544                       "at " INTPTR_FORMAT
 545                       ", unguarding " INTPTR_FORMAT ": %s, errno=%d", p2i(addr),
 546                       p2i(page_start), (res ? "success" : "failed"), errno);
 547         stub = pc;
 548 
 549         // Set last_addr so if we fault again at the same address, we don't end
 550         // up in an endless loop.
 551         //
 552         // There are two potential complications here.  Two threads trapping at
 553         // the same address at the same time could cause one of the threads to
 554         // think it already unguarded, and abort the VM.  Likely very rare.
 555         //
 556         // The other race involves two threads alternately trapping at
 557         // different addresses and failing to unguard the page, resulting in
 558         // an endless loop.  This condition is probably even more unlikely than
 559         // the first.
 560         //
 561         // Although both cases could be avoided by using locks or thread local
 562         // last_addr, these solutions are unnecessary complication: this
 563         // handler is a best-effort safety net, not a complete solution.  It is
 564         // disabled by default and should only be used as a workaround in case
 565         // we missed any no-execute-unsafe VM code.
 566 
 567         last_addr = addr;
 568       }
 569     }
 570   }
 571 #endif // !AMD64
 572 
 573   if (stub != NULL) {
 574     // save all thread context in case we need to restore it
 575     if (thread != NULL) thread->set_saved_exception_pc(pc);
 576 
 577     os::Linux::ucontext_set_pc(uc, stub);
 578     return true;
 579   }
 580 
 581   // signal-chaining
 582   if (os::Linux::chained_handler(sig, info, ucVoid)) {
 583      return true;
 584   }
 585 
 586   if (!abort_if_unrecognized) {
 587     // caller wants another chance, so give it to him
 588     return false;
 589   }
 590 
 591   if (pc == NULL && uc != NULL) {
 592     pc = os::Linux::ucontext_get_pc(uc);
 593   }
 594 
 595   // unmask current signal
 596   sigset_t newset;
 597   sigemptyset(&newset);
 598   sigaddset(&newset, sig);
 599   sigprocmask(SIG_UNBLOCK, &newset, NULL);
 600 
 601   VMError::report_and_die(t, sig, pc, info, ucVoid);
 602 
 603   ShouldNotReachHere();
 604   return true; // Mute compiler
 605 }
 606 
 607 void os::Linux::init_thread_fpu_state(void) {
 608 #ifndef AMD64
 609   // set fpu to 53 bit precision
 610   set_fpu_control_word(0x27f);
 611 #endif // !AMD64
 612 }
 613 
 614 int os::Linux::get_fpu_control_word(void) {
 615 #ifdef AMD64
 616   return 0;
 617 #else
 618   int fpu_control;
 619   _FPU_GETCW(fpu_control);
 620   return fpu_control & 0xffff;
 621 #endif // AMD64
 622 }
 623 
 624 void os::Linux::set_fpu_control_word(int fpu_control) {
 625 #ifndef AMD64
 626   _FPU_SETCW(fpu_control);
 627 #endif // !AMD64
 628 }
 629 
 630 // Check that the linux kernel version is 2.4 or higher since earlier
 631 // versions do not support SSE without patches.
 632 bool os::supports_sse() {
 633 #ifdef AMD64
 634   return true;
 635 #else
 636   struct utsname uts;
 637   if( uname(&uts) != 0 ) return false; // uname fails?
 638   char *minor_string;
 639   int major = strtol(uts.release,&minor_string,10);
 640   int minor = strtol(minor_string+1,NULL,10);
 641   bool result = (major > 2 || (major==2 && minor >= 4));
 642   log_info(os)("OS version is %d.%d, which %s support SSE/SSE2",
 643                major,minor, result ? "DOES" : "does NOT");
 644   return result;
 645 #endif // AMD64
 646 }
 647 
 648 bool os::is_allocatable(size_t bytes) {
 649 #ifdef AMD64
 650   // unused on amd64?
 651   return true;
 652 #else
 653 
 654   if (bytes < 2 * G) {
 655     return true;
 656   }
 657 
 658   char* addr = reserve_memory(bytes, NULL);
 659 
 660   if (addr != NULL) {
 661     release_memory(addr, bytes);
 662   }
 663 
 664   return addr != NULL;
 665 #endif // AMD64
 666 }
 667 
 668 ////////////////////////////////////////////////////////////////////////////////
 669 // thread stack
 670 
 671 #ifdef AMD64
 672 size_t os::Linux::min_stack_allowed  = 64 * K;
 673 #else
 674 size_t os::Linux::min_stack_allowed  =  (48 DEBUG_ONLY(+4))*K;
 675 #endif // AMD64
 676 
 677 // return default stack size for thr_type
 678 size_t os::Linux::default_stack_size(os::ThreadType thr_type) {
 679   // default stack size (compiler thread needs larger stack)
 680 #ifdef AMD64
 681   size_t s = (thr_type == os::compiler_thread ? 4 * M : 1 * M);
 682 #else
 683   size_t s = (thr_type == os::compiler_thread ? 2 * M : 512 * K);
 684 #endif // AMD64
 685   return s;
 686 }
 687 
 688 size_t os::Linux::default_guard_size(os::ThreadType thr_type) {
 689   // Creating guard page is very expensive. Java thread has HotSpot
 690   // guard page, only enable glibc guard page for non-Java threads.
 691   return (thr_type == java_thread ? 0 : page_size());
 692 }
 693 
 694 // Java thread:
 695 //
 696 //   Low memory addresses
 697 //    +------------------------+
 698 //    |                        |\  JavaThread created by VM does not have glibc
 699 //    |    glibc guard page    | - guard, attached Java thread usually has
 700 //    |                        |/  1 page glibc guard.
 701 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()
 702 //    |                        |\
 703 //    |  HotSpot Guard Pages   | - red and yellow pages
 704 //    |                        |/
 705 //    +------------------------+ JavaThread::stack_yellow_zone_base()
 706 //    |                        |\
 707 //    |      Normal Stack      | -
 708 //    |                        |/
 709 // P2 +------------------------+ Thread::stack_base()
 710 //
 711 // Non-Java thread:
 712 //
 713 //   Low memory addresses
 714 //    +------------------------+
 715 //    |                        |\
 716 //    |  glibc guard page      | - usually 1 page
 717 //    |                        |/
 718 // P1 +------------------------+ Thread::stack_base() - Thread::stack_size()
 719 //    |                        |\
 720 //    |      Normal Stack      | -
 721 //    |                        |/
 722 // P2 +------------------------+ Thread::stack_base()
 723 //
 724 // ** P1 (aka bottom) and size ( P2 = P1 - size) are the address and stack size returned from
 725 //    pthread_attr_getstack()
 726 
 727 static void current_stack_region(address * bottom, size_t * size) {
 728   if (os::Linux::is_initial_thread()) {
 729      // initial thread needs special handling because pthread_getattr_np()
 730      // may return bogus value.
 731      *bottom = os::Linux::initial_thread_stack_bottom();
 732      *size   = os::Linux::initial_thread_stack_size();
 733   } else {
 734      pthread_attr_t attr;
 735 
 736      int rslt = pthread_getattr_np(pthread_self(), &attr);
 737 
 738      // JVM needs to know exact stack location, abort if it fails
 739      if (rslt != 0) {
 740        if (rslt == ENOMEM) {
 741          vm_exit_out_of_memory(0, OOM_MMAP_ERROR, "pthread_getattr_np");
 742        } else {
 743          fatal("pthread_getattr_np failed with errno = %d", rslt);
 744        }
 745      }
 746 
 747      if (pthread_attr_getstack(&attr, (void **)bottom, size) != 0) {
 748          fatal("Can not locate current stack attributes!");
 749      }
 750 
 751      pthread_attr_destroy(&attr);
 752 
 753   }
 754   assert(os::current_stack_pointer() >= *bottom &&
 755          os::current_stack_pointer() < *bottom + *size, "just checking");
 756 }
 757 
 758 address os::current_stack_base() {
 759   address bottom;
 760   size_t size;
 761   current_stack_region(&bottom, &size);
 762   return (bottom + size);
 763 }
 764 
 765 size_t os::current_stack_size() {
 766   // stack size includes normal stack and HotSpot guard pages
 767   address bottom;
 768   size_t size;
 769   current_stack_region(&bottom, &size);
 770   return size;
 771 }
 772 
 773 /////////////////////////////////////////////////////////////////////////////
 774 // helper functions for fatal error handler
 775 
 776 void os::print_context(outputStream *st, const void *context) {
 777   if (context == NULL) return;
 778 
 779   const ucontext_t *uc = (const ucontext_t*)context;
 780   st->print_cr("Registers:");
 781 #ifdef AMD64
 782   st->print(  "RAX=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RAX]);
 783   st->print(", RBX=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RBX]);
 784   st->print(", RCX=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RCX]);
 785   st->print(", RDX=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RDX]);
 786   st->cr();
 787   st->print(  "RSP=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RSP]);
 788   st->print(", RBP=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RBP]);
 789   st->print(", RSI=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RSI]);
 790   st->print(", RDI=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RDI]);
 791   st->cr();
 792   st->print(  "R8 =" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R8]);
 793   st->print(", R9 =" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R9]);
 794   st->print(", R10=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R10]);
 795   st->print(", R11=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R11]);
 796   st->cr();
 797   st->print(  "R12=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R12]);
 798   st->print(", R13=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R13]);
 799   st->print(", R14=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R14]);
 800   st->print(", R15=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_R15]);
 801   st->cr();
 802   st->print(  "RIP=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_RIP]);
 803   st->print(", EFLAGS=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_EFL]);
 804   st->print(", CSGSFS=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_CSGSFS]);
 805   st->print(", ERR=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_ERR]);
 806   st->cr();
 807   st->print("  TRAPNO=" INTPTR_FORMAT, (intptr_t)uc->uc_mcontext.gregs[REG_TRAPNO]);
 808 #else
 809   st->print(  "EAX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EAX]);
 810   st->print(", EBX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EBX]);
 811   st->print(", ECX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_ECX]);
 812   st->print(", EDX=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EDX]);
 813   st->cr();
 814   st->print(  "ESP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_UESP]);
 815   st->print(", EBP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EBP]);
 816   st->print(", ESI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_ESI]);
 817   st->print(", EDI=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EDI]);
 818   st->cr();
 819   st->print(  "EIP=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EIP]);
 820   st->print(", EFLAGS=" INTPTR_FORMAT, uc->uc_mcontext.gregs[REG_EFL]);
 821   st->print(", CR2=" PTR64_FORMAT, (uint64_t)uc->uc_mcontext.cr2);
 822 #endif // AMD64
 823   st->cr();
 824   st->cr();
 825 
 826   intptr_t *sp = (intptr_t *)os::Linux::ucontext_get_sp(uc);
 827   st->print_cr("Top of Stack: (sp=" PTR_FORMAT ")", p2i(sp));
 828   print_hex_dump(st, (address)sp, (address)(sp + 8), sizeof(intptr_t));
 829   st->cr();
 830 
 831   // Note: it may be unsafe to inspect memory near pc. For example, pc may
 832   // point to garbage if entry point in an nmethod is corrupted. Leave
 833   // this at the end, and hope for the best.
 834   address pc = os::Linux::ucontext_get_pc(uc);
 835   st->print_cr("Instructions: (pc=" PTR_FORMAT ")", p2i(pc));
 836   print_hex_dump(st, pc - 32, pc + 32, sizeof(char));
 837 }
 838 
 839 void os::print_register_info(outputStream *st, const void *context) {
 840   if (context == NULL) return;
 841 
 842   const ucontext_t *uc = (const ucontext_t*)context;
 843 
 844   st->print_cr("Register to memory mapping:");
 845   st->cr();
 846 
 847   // this is horrendously verbose but the layout of the registers in the
 848   // context does not match how we defined our abstract Register set, so
 849   // we can't just iterate through the gregs area
 850 
 851   // this is only for the "general purpose" registers
 852 
 853 #ifdef AMD64
 854   st->print("RAX="); print_location(st, uc->uc_mcontext.gregs[REG_RAX]);
 855   st->print("RBX="); print_location(st, uc->uc_mcontext.gregs[REG_RBX]);
 856   st->print("RCX="); print_location(st, uc->uc_mcontext.gregs[REG_RCX]);
 857   st->print("RDX="); print_location(st, uc->uc_mcontext.gregs[REG_RDX]);
 858   st->print("RSP="); print_location(st, uc->uc_mcontext.gregs[REG_RSP]);
 859   st->print("RBP="); print_location(st, uc->uc_mcontext.gregs[REG_RBP]);
 860   st->print("RSI="); print_location(st, uc->uc_mcontext.gregs[REG_RSI]);
 861   st->print("RDI="); print_location(st, uc->uc_mcontext.gregs[REG_RDI]);
 862   st->print("R8 ="); print_location(st, uc->uc_mcontext.gregs[REG_R8]);
 863   st->print("R9 ="); print_location(st, uc->uc_mcontext.gregs[REG_R9]);
 864   st->print("R10="); print_location(st, uc->uc_mcontext.gregs[REG_R10]);
 865   st->print("R11="); print_location(st, uc->uc_mcontext.gregs[REG_R11]);
 866   st->print("R12="); print_location(st, uc->uc_mcontext.gregs[REG_R12]);
 867   st->print("R13="); print_location(st, uc->uc_mcontext.gregs[REG_R13]);
 868   st->print("R14="); print_location(st, uc->uc_mcontext.gregs[REG_R14]);
 869   st->print("R15="); print_location(st, uc->uc_mcontext.gregs[REG_R15]);
 870 #else
 871   st->print("EAX="); print_location(st, uc->uc_mcontext.gregs[REG_EAX]);
 872   st->print("EBX="); print_location(st, uc->uc_mcontext.gregs[REG_EBX]);
 873   st->print("ECX="); print_location(st, uc->uc_mcontext.gregs[REG_ECX]);
 874   st->print("EDX="); print_location(st, uc->uc_mcontext.gregs[REG_EDX]);
 875   st->print("ESP="); print_location(st, uc->uc_mcontext.gregs[REG_ESP]);
 876   st->print("EBP="); print_location(st, uc->uc_mcontext.gregs[REG_EBP]);
 877   st->print("ESI="); print_location(st, uc->uc_mcontext.gregs[REG_ESI]);
 878   st->print("EDI="); print_location(st, uc->uc_mcontext.gregs[REG_EDI]);
 879 #endif // AMD64
 880 
 881   st->cr();
 882 }
 883 
 884 void os::setup_fpu() {
 885 #ifndef AMD64
 886   address fpu_cntrl = StubRoutines::addr_fpu_cntrl_wrd_std();
 887   __asm__ volatile (  "fldcw (%0)" :
 888                       : "r" (fpu_cntrl) : "memory");
 889 #endif // !AMD64
 890 }
 891 
 892 #ifndef PRODUCT
 893 void os::verify_stack_alignment() {
 894 #ifdef AMD64
 895   assert(((intptr_t)os::current_stack_pointer() & (StackAlignmentInBytes-1)) == 0, "incorrect stack alignment");
 896 #endif
 897 }
 898 #endif
 899 
 900 
 901 /*
 902  * IA32 only: execute code at a high address in case buggy NX emulation is present. I.e. avoid CS limit
 903  * updates (JDK-8023956).
 904  */
 905 void os::workaround_expand_exec_shield_cs_limit() {
 906 #if defined(IA32)
 907   size_t page_size = os::vm_page_size();
 908   /*
 909    * Take the highest VA the OS will give us and exec
 910    *
 911    * Although using -(pagesz) as mmap hint works on newer kernel as you would
 912    * think, older variants affected by this work-around don't (search forward only).
 913    *
 914    * On the affected distributions, we understand the memory layout to be:
 915    *
 916    *   TASK_LIMIT= 3G, main stack base close to TASK_LIMT.
 917    *
 918    * A few pages south main stack will do it.
 919    *
 920    * If we are embedded in an app other than launcher (initial != main stack),
 921    * we don't have much control or understanding of the address space, just let it slide.
 922    */
 923   char* hint = (char*)(Linux::initial_thread_stack_bottom() -
 924                        (JavaThread::stack_guard_zone_size() + page_size));
 925   char* codebuf = os::attempt_reserve_memory_at(page_size, hint);
 926   if ((codebuf == NULL) || (!os::commit_memory(codebuf, page_size, true))) {
 927     return; // No matter, we tried, best effort.
 928   }
 929 
 930   MemTracker::record_virtual_memory_type((address)codebuf, mtInternal);
 931 
 932   log_info(os)("[CS limit NX emulation work-around, exec code at: %p]", codebuf);
 933 
 934   // Some code to exec: the 'ret' instruction
 935   codebuf[0] = 0xC3;
 936 
 937   // Call the code in the codebuf
 938   __asm__ volatile("call *%0" : : "r"(codebuf));
 939 
 940   // keep the page mapped so CS limit isn't reduced.
 941 #endif
 942 }
 943 
 944 int os::extra_bang_size_in_bytes() {
 945   // JDK-8050147 requires the full cache line bang for x86.
 946   return VM_Version::L1_line_size();
 947 }