gecko-dev/toolkit/components/backgroundhangmonitor/ThreadStackHelper.cpp

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* 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 "nsJSPrincipals.h"
#include "nsScriptSecurityManager.h"
#include "jsfriendapi.h"
#ifdef MOZ_THREADSTACKHELPER_PROFILING_STACK
#  include "js/ProfilingStack.h"
#endif

#include <utility>

#include "mozilla/Assertions.h"
#include "mozilla/Attributes.h"
#include "mozilla/BasePrincipal.h"
#include "mozilla/HangTypes.h"
#include "mozilla/IntegerPrintfMacros.h"
#include "mozilla/MemoryChecking.h"
#include "mozilla/Scoped.h"
#include "mozilla/Sprintf.h"
#include "mozilla/UniquePtr.h"
#include "nsThread.h"

#ifdef __GNUC__
#  pragma GCC diagnostic push
#  pragma GCC diagnostic ignored "-Wshadow"
#endif

#if defined(MOZ_VALGRIND)
#  include <valgrind/valgrind.h>
#endif

#include <string.h>
#include <vector>
#include <cstdlib>

#ifdef XP_LINUX
#  include <ucontext.h>
#  include <unistd.h>
#  include <sys/syscall.h>
#endif

#ifdef __GNUC__
#  pragma GCC diagnostic pop  // -Wshadow
#endif

#if defined(XP_LINUX) || defined(XP_MACOSX)
#  include <pthread.h>
#endif

#ifdef ANDROID
#  ifndef SYS_gettid
#    define SYS_gettid __NR_gettid
#  endif
#  if defined(__arm__) && !defined(__NR_rt_tgsigqueueinfo)
// Some NDKs don't define this constant even though the kernel supports it.
#    define __NR_rt_tgsigqueueinfo (__NR_SYSCALL_BASE + 363)
#  endif
#  ifndef SYS_rt_tgsigqueueinfo
#    define SYS_rt_tgsigqueueinfo __NR_rt_tgsigqueueinfo
#  endif
#endif

namespace mozilla {

// A character which we append to any string which gets truncated as a a
// result of trying to write it into a statically allocated buffer. This just
// makes it a little easier to know that the buffer was truncated during
// analysis.
const char kTruncationIndicator = '$';

ThreadStackHelper::ThreadStackHelper()
    : mStackToFill(nullptr),
      mMaxStackSize(16),
      mMaxBufferSize(512),
      mDesiredStackSize(0),
      mDesiredBufferSize(0) {
  mThreadId = profiler_current_thread_id();
}

bool ThreadStackHelper::PrepareStackBuffer(HangStack& aStack) {
  // If we need to grow because we used more than we could store last time,
  // increase our maximum sizes for this time.
  if (mDesiredBufferSize > mMaxBufferSize) {
    mMaxBufferSize = mDesiredBufferSize;
  }
  if (mDesiredStackSize > mMaxStackSize) {
    mMaxStackSize = mDesiredStackSize;
  }
  mDesiredBufferSize = 0;
  mDesiredStackSize = 0;

  // Clear all of the stack entries.
  aStack.stack().ClearAndRetainStorage();
  aStack.strbuffer().ClearAndRetainStorage();
  aStack.modules().Clear();

#ifdef MOZ_THREADSTACKHELPER_PROFILING_STACK
  // Ensure we have enough space in our stack and string buffers for the data we
  // want to collect.
  if (!aStack.stack().SetCapacity(mMaxStackSize, fallible) ||
      !aStack.strbuffer().SetCapacity(mMaxBufferSize, fallible)) {
    return false;
  }
  return true;
#else
  return false;
#endif
}

namespace {
template <typename T>
class ScopedSetPtr {
 private:
  T*& mPtr;

 public:
  ScopedSetPtr(T*& p, T* val) : mPtr(p) { mPtr = val; }
  ~ScopedSetPtr() { mPtr = nullptr; }
};
}  // namespace

void ThreadStackHelper::GetStack(HangStack& aStack, nsACString& aRunnableName,
                                 bool aStackWalk) {
  aRunnableName.AssignLiteral("???");

  if (!PrepareStackBuffer(aStack)) {
    return;
  }

  Array<char, nsThread::kRunnableNameBufSize> runnableName;
  runnableName[0] = '\0';

  ScopedSetPtr<HangStack> _stackGuard(mStackToFill, &aStack);
  ScopedSetPtr<Array<char, nsThread::kRunnableNameBufSize>> _runnableGuard(
      mRunnableNameBuffer, &runnableName);

  // XXX: We don't need to pass in ProfilerFeature::StackWalk to trigger
  // stackwalking, as that is instead controlled by the last argument.
  profiler_suspend_and_sample_thread(mThreadId, ProfilerFeature::Privacy, *this,
                                     aStackWalk);

  // Copy the name buffer allocation into the output string. We explicitly set
  // the last byte to null in case we read in some corrupted data without a null
  // terminator.
  runnableName[nsThread::kRunnableNameBufSize - 1] = '\0';
  aRunnableName.AssignASCII(runnableName.cbegin());
}

void ThreadStackHelper::SetIsMainThread() {
  MOZ_RELEASE_ASSERT(mRunnableNameBuffer);

  // NOTE: We cannot allocate any memory in this callback, as the target
  // thread is suspended, so we first copy it into a stack-allocated buffer,
  // and then once the target thread is resumed, we can copy it into a real
  // nsCString.
  //
  // Currently we only store the names of runnables which are running on the
  // main thread, so we only want to read sMainThreadRunnableName and copy its
  // value in the case that we are currently suspending the main thread.
  *mRunnableNameBuffer = nsThread::sMainThreadRunnableName;
}

void ThreadStackHelper::TryAppendFrame(HangEntry aFrame) {
  MOZ_RELEASE_ASSERT(mStackToFill);

  // We deduplicate identical Content, Jit, Wasm, ChromeScript and Suppressed
  // frames.
  switch (aFrame.type()) {
    case HangEntry::THangEntryContent:
    case HangEntry::THangEntryJit:
    case HangEntry::THangEntryWasm:
    case HangEntry::THangEntryChromeScript:
    case HangEntry::THangEntrySuppressed:
      if (!mStackToFill->stack().IsEmpty() &&
          mStackToFill->stack().LastElement().type() == aFrame.type()) {
        return;
      }
      break;
    default:
      break;
  }

  // Record that we _want_ to use another frame entry. If this exceeds
  // mMaxStackSize, we'll allocate more room on the next hang.
  mDesiredStackSize += 1;

  // Perform the append if we have enough space to do so.
  if (mStackToFill->stack().Capacity() > mStackToFill->stack().Length()) {
    mStackToFill->stack().AppendElement(std::move(aFrame));
  }
}

void ThreadStackHelper::CollectNativeLeafAddr(void* aAddr) {
  MOZ_RELEASE_ASSERT(mStackToFill);
  TryAppendFrame(HangEntryProgCounter(reinterpret_cast<uintptr_t>(aAddr)));
}

void ThreadStackHelper::CollectJitReturnAddr(void* aAddr) {
  MOZ_RELEASE_ASSERT(mStackToFill);
  TryAppendFrame(HangEntryJit());
}

void ThreadStackHelper::CollectWasmFrame(const char* aLabel) {
  MOZ_RELEASE_ASSERT(mStackToFill);
  // We don't want to collect WASM frames, as they are probably for content, so
  // we just add a "(content wasm)" frame.
  TryAppendFrame(HangEntryWasm());
}

namespace {

bool IsChromeJSScript(JSScript* aScript) {
  // May be called from another thread or inside a signal handler.
  // We assume querying the script is safe but we must not manipulate it.

  JSPrincipals* const principals = JS_GetScriptPrincipals(aScript);
  return nsJSPrincipals::get(principals)->IsSystemPrincipal();
}

// Get the full path after the URI scheme, if the URI matches the scheme.
// For example, GetFullPathForScheme("a://b/c/d/e", "a://") returns "b/c/d/e".
template <size_t LEN>
const char* GetFullPathForScheme(const char* filename,
                                 const char (&scheme)[LEN]) {
  // Account for the null terminator included in LEN.
  if (!strncmp(filename, scheme, LEN - 1)) {
    return filename + LEN - 1;
  }
  return nullptr;
}

// Get the full path after a URI component, if the URI contains the component.
// For example, GetPathAfterComponent("a://b/c/d/e", "/c/") returns "d/e".
template <size_t LEN>
const char* GetPathAfterComponent(const char* filename,
                                  const char (&component)[LEN]) {
  const char* found = nullptr;
  const char* next = strstr(filename, component);
  while (next) {
    // Move 'found' to end of the component, after the separator '/'.
    // 'LEN - 1' accounts for the null terminator included in LEN,
    found = next + LEN - 1;
    // Resume searching before the separator '/'.
    next = strstr(found - 1, component);
  }
  return found;
}

}  // namespace

bool ThreadStackHelper::MaybeAppendDynamicStackFrame(Span<const char> aBuf) {
  mDesiredBufferSize += aBuf.Length() + 1;

  if (mStackToFill->stack().Capacity() > mStackToFill->stack().Length() &&
      (mStackToFill->strbuffer().Capacity() -
       mStackToFill->strbuffer().Length()) > aBuf.Length() + 1) {
    // NOTE: We only increment this if we're going to successfully append.
    mDesiredStackSize += 1;
    uint32_t start = mStackToFill->strbuffer().Length();
    mStackToFill->strbuffer().AppendElements(aBuf.Elements(), aBuf.Length());
    mStackToFill->strbuffer().AppendElement('\0');
    mStackToFill->stack().AppendElement(HangEntryBufOffset(start));
    return true;
  }
  return false;
}

void ThreadStackHelper::CollectProfilingStackFrame(
    const js::ProfilingStackFrame& aFrame) {
  // For non-js frames, first try to get the dynamic string and fit it in,
  // otherwise just get the label.
  if (!aFrame.isJsFrame()) {
    const char* frameLabel = aFrame.label();
    if (aFrame.isNonsensitive() && aFrame.dynamicString()) {
      const char* dynamicString = aFrame.dynamicString();
      char buffer[128];
      size_t len = SprintfLiteral(buffer, "%s %s", frameLabel, dynamicString);
      if (len > sizeof(buffer)) {
        buffer[sizeof(buffer) - 1] = kTruncationIndicator;
        len = sizeof(buffer);
      }
      if (MaybeAppendDynamicStackFrame(MakeSpan(buffer, len))) {
        return;
      }
    }

    // frameLabel is a statically allocated string, so we want to store a
    // reference to it without performing any allocations. This is important, as
    // we aren't allowed to allocate within this function.
    //
    // The variant for this kind of label in our HangStack object is a
    // `nsCString`, which normally contains heap allocated string data. However,
    // `nsCString` has an optimization for literal strings which causes the
    // backing data to not be copied when being copied between nsCString
    // objects.
    //
    // We take advantage of that optimization by creating a nsCString object
    // which has the LITERAL flag set. Without this optimization, this code
    // would be incorrect.
    nsCString label;
    label.AssignLiteral(frameLabel, strlen(frameLabel));

    // Let's make sure we don't deadlock here, by asserting that `label`'s
    // backing data matches.
    MOZ_RELEASE_ASSERT(label.BeginReading() == frameLabel,
                       "String copy performed during "
                       "ThreadStackHelper::CollectProfilingStackFrame");
    TryAppendFrame(label);
    return;
  }

  if (!aFrame.script()) {
    TryAppendFrame(HangEntrySuppressed());
    return;
  }

  if (!IsChromeJSScript(aFrame.script())) {
    TryAppendFrame(HangEntryContent());
    return;
  }

  // Rather than using the profiler's dynamic string, we compute our own string.
  // This is because we want to do some size-saving strategies, and throw out
  // information which won't help us as much.
  // XXX: We currently don't collect the function name which hung.
  const char* filename = JS_GetScriptFilename(aFrame.script());
  unsigned lineno = JS_PCToLineNumber(aFrame.script(), aFrame.pc());

  // Some script names are in the form "foo -> bar -> baz".
  // Here we find the origin of these redirected scripts.
  const char* basename = GetPathAfterComponent(filename, " -> ");
  if (basename) {
    filename = basename;
  }

  // Strip chrome:// or resource:// off of the filename if present.
  basename = GetFullPathForScheme(filename, "chrome://");
  if (!basename) {
    basename = GetFullPathForScheme(filename, "resource://");
  }
  if (!basename) {
    // If we're in an add-on script, under the {profile}/extensions
    // directory, extract the path after the /extensions/ part.
    basename = GetPathAfterComponent(filename, "/extensions/");
  }
  if (!basename) {
    // Only keep the file base name for paths outside the above formats.
    basename = strrchr(filename, '/');
    basename = basename ? basename + 1 : filename;
    // Look for Windows path separator as well.
    filename = strrchr(basename, '\\');
    if (filename) {
      basename = filename + 1;
    }
  }

  char buffer[128];  // Enough to fit longest js file name from the tree
  size_t len = SprintfLiteral(buffer, "%s:%u", basename, lineno);
  if (len > sizeof(buffer)) {
    buffer[sizeof(buffer) - 1] = kTruncationIndicator;
    len = sizeof(buffer);
  }
  if (MaybeAppendDynamicStackFrame(MakeSpan(buffer, len))) {
    return;
  }

  TryAppendFrame(HangEntryChromeScript());
}

}  // namespace mozilla