The Tor Browser: xpcom/threads/ThreadStackHelper.cpp@b8a032363ba2 (annotated)

xpcom/threads/ThreadStackHelper.cpp@b8a032363ba2 (annotated)

xpcom/threads/ThreadStackHelper.cpp

Thu, 22 Jan 2015 13:21:57 +0100

author: Michael Schloh von Bennewitz <michael@schloh.com>
date: Thu, 22 Jan 2015 13:21:57 +0100
branch: TOR_BUG_9701
changeset 15: b8a032363ba2
permissions: -rw-r--r--

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 /* This Source Code Form is subject to the terms of the Mozilla Public
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 #include "ThreadStackHelper.h"
 #include "MainThreadUtils.h"
 #include "mozilla/Assertions.h"
 #include "mozilla/Move.h"
 #ifdef XP_LINUX
 #include <unistd.h>
 #include <sys/syscall.h>
 #endif
 #ifdef ANDROID
 #ifndef SYS_gettid
 #define SYS_gettid __NR_gettid
 #endif
 #ifndef SYS_tgkill
 #define SYS_tgkill __NR_tgkill
 #endif
 #endif
 namespace mozilla {
 void
 ThreadStackHelper::Startup()
 {
 #if defined(XP_LINUX)
   MOZ_ASSERT(NS_IsMainThread());
   if (!sInitialized) {
     MOZ_ALWAYS_TRUE(!::sem_init(&sSem, 0, 0));
   }
   sInitialized++;
 #endif
 }
 void
 ThreadStackHelper::Shutdown()
 {
 #if defined(XP_LINUX)
   MOZ_ASSERT(NS_IsMainThread());
   if (sInitialized == 1) {
     MOZ_ALWAYS_TRUE(!::sem_destroy(&sSem));
   }
   sInitialized--;
 #endif
 }
 ThreadStackHelper::ThreadStackHelper()
   :
 #ifdef MOZ_ENABLE_PROFILER_SPS
     mPseudoStack(mozilla_get_pseudo_stack()),
 #endif
     mStackBuffer()
   , mMaxStackSize(mStackBuffer.capacity())
 {
 #if defined(XP_LINUX)
   mThreadID = ::syscall(SYS_gettid);
 #elif defined(XP_WIN)
   mInitialized = !!::DuplicateHandle(
     ::GetCurrentProcess(), ::GetCurrentThread(),
     ::GetCurrentProcess(), &mThreadID,
     THREAD_SUSPEND_RESUME, FALSE, 0);
   MOZ_ASSERT(mInitialized);
 #elif defined(XP_MACOSX)
   mThreadID = mach_thread_self();
 #endif
 }
 ThreadStackHelper::~ThreadStackHelper()
 {
 #if defined(XP_WIN)
   if (mInitialized) {
     MOZ_ALWAYS_TRUE(!!::CloseHandle(mThreadID));
   }
 #endif
 }
 #if defined(XP_LINUX) && defined(__arm__)
 // Some (old) Linux kernels on ARM have a bug where a signal handler
 // can be called without clearing the IT bits in CPSR first. The result
 // is that the first few instructions of the handler could be skipped,
 // ultimately resulting in crashes. To workaround this bug, the handler
 // on ARM is a trampoline that starts with enough NOP instructions, so
 // that even if the IT bits are not cleared, only the NOP instructions
 // will be skipped over.
 template <void (*H)(int, siginfo_t*, void*)>
 __attribute__((naked)) void
 SignalTrampoline(int aSignal, siginfo_t* aInfo, void* aContext)
 {
   asm volatile (
     "nop; nop; nop; nop"
     : : : "memory");
   // Because the assembler may generate additional insturctions below, we
   // need to ensure NOPs are inserted first by separating them out above.
   asm volatile (
     "bx %0"
     :
     : "r"(H), "l"(aSignal), "l"(aInfo), "l"(aContext)
     : "memory");
 }
 #endif // XP_LINUX && __arm__
 void
 ThreadStackHelper::GetStack(Stack& aStack)
 {
   // Always run PrepareStackBuffer first to clear aStack
   if (!PrepareStackBuffer(aStack)) {
     // Skip and return empty aStack
     return;
   }
 #if defined(XP_LINUX)
   if (profiler_is_active()) {
     // Profiler can interfere with our Linux signal handling
     return;
   }
   if (!sInitialized) {
     MOZ_ASSERT(false);
     return;
   }
   sCurrent = this;
   struct sigaction sigact = {};
 #ifdef __arm__
   sigact.sa_sigaction = SignalTrampoline<SigAction>;
 #else
   sigact.sa_sigaction = SigAction;
 #endif
   sigemptyset(&sigact.sa_mask);
   sigact.sa_flags = SA_SIGINFO | SA_RESTART;
   if (::sigaction(SIGPROF, &sigact, &sOldSigAction)) {
     MOZ_ASSERT(false);
     return;
   }
   MOZ_ALWAYS_TRUE(!::syscall(SYS_tgkill, getpid(), mThreadID, SIGPROF));
   MOZ_ALWAYS_TRUE(!::sem_wait(&sSem));
 #elif defined(XP_WIN)
   if (!mInitialized) {
     MOZ_ASSERT(false);
     return;
   }
   if (::SuspendThread(mThreadID) == DWORD(-1)) {
     MOZ_ASSERT(false);
     return;
   }
   FillStackBuffer();
   MOZ_ALWAYS_TRUE(::ResumeThread(mThreadID) != DWORD(-1));
 #elif defined(XP_MACOSX)
   if (::thread_suspend(mThreadID) != KERN_SUCCESS) {
     MOZ_ASSERT(false);
     return;
   }
   FillStackBuffer();
   MOZ_ALWAYS_TRUE(::thread_resume(mThreadID) == KERN_SUCCESS);
 #endif
   aStack = Move(mStackBuffer);
 }
 #ifdef XP_LINUX
 int ThreadStackHelper::sInitialized;
 sem_t ThreadStackHelper::sSem;
 struct sigaction ThreadStackHelper::sOldSigAction;
 ThreadStackHelper* ThreadStackHelper::sCurrent;
 void
 ThreadStackHelper::SigAction(int aSignal, siginfo_t* aInfo, void* aContext)
 {
   ::sigaction(SIGPROF, &sOldSigAction, nullptr);
   sCurrent->FillStackBuffer();
   sCurrent = nullptr;
   ::sem_post(&sSem);
 }
 #endif // XP_LINUX
 bool
 ThreadStackHelper::PrepareStackBuffer(Stack& aStack) {
   // Return false to skip getting the stack and return an empty stack
   aStack.clear();
 #ifdef MOZ_ENABLE_PROFILER_SPS
   /* Normally, provided the profiler is enabled, it would be an error if we
      don't have a pseudostack here (the thread probably forgot to call
      profiler_register_thread). However, on B2G, profiling secondary threads
      may be disabled despite profiler being enabled. This is by-design and
      is not an error. */
 #ifdef MOZ_WIDGET_GONK
   if (!mPseudoStack) {
     return false;
   }
 #endif
   MOZ_ASSERT(mPseudoStack);
   mStackBuffer.clear();
   MOZ_ALWAYS_TRUE(mStackBuffer.reserve(mMaxStackSize));
   return true;
 #else
   return false;
 #endif
 }
 void
 ThreadStackHelper::FillStackBuffer() {
 #ifdef MOZ_ENABLE_PROFILER_SPS
   size_t reservedSize = mMaxStackSize;
   // Go from front to back
   const volatile StackEntry* entry = mPseudoStack->mStack;
   const volatile StackEntry* end = entry + mPseudoStack->stackSize();
   // Deduplicate identical, consecutive frames
   const char* prevLabel = nullptr;
   for (; reservedSize-- && entry != end; entry++) {
     /* We only accept non-copy labels, because
        we are unable to actually copy labels here */
     if (entry->isCopyLabel()) {
       continue;
     }
     const char* const label = entry->label();
     if (label == prevLabel) {
       continue;
     }
     mStackBuffer.infallibleAppend(label);
     prevLabel = label;
   }
   // If we exited early due to buffer size, expand the buffer for next time
   mMaxStackSize += (end - entry);
 #endif
 }
 } // namespace mozilla

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xpcom/threads/ThreadStackHelper.cpp@b8a032363ba2 (annotated)

xpcom/threads/ThreadStackHelper.cpp