Source code

Revision control

Other Tools

/* -*- 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 */
// There are three kinds of samples done by the profiler.
// - A "periodic" sample is the most complex kind. It is done in response to a
// timer while the profiler is active. It involves writing a stack trace plus
// a variety of other values (memory measurements, responsiveness
// measurements, etc.) into the main ProfileBuffer. The sampling is done from
// off-thread, and so SuspendAndSampleAndResumeThread() is used to get the
// register values.
// - A "synchronous" sample is a simpler kind. It is done in response to an API
// call (profiler_get_backtrace()). It involves writing a stack trace and
// little else into a temporary ProfileBuffer, and wrapping that up in a
// ProfilerBacktrace that can be subsequently used in a marker. The sampling
// is done on-thread, and so Registers::SyncPopulate() is used to get the
// register values.
// - A "backtrace" sample is the simplest kind. It is done in response to an
// API call (profiler_suspend_and_sample_thread()). It involves getting a
// stack trace via a ProfilerStackCollector; it does not write to a
// ProfileBuffer. The sampling is done from off-thread, and so uses
// SuspendAndSampleAndResumeThread() to get the register values.
#include "platform.h"
#include <algorithm>
#include <errno.h>
#include <fstream>
#include <ostream>
#include <set>
#include <sstream>
// #include "memory_hooks.h"
#include "mozilla/ArrayUtils.h"
#include "mozilla/Atomics.h"
#include "mozilla/AutoProfilerLabel.h"
#include "mozilla/BaseProfilerDetail.h"
#include "mozilla/DoubleConversion.h"
#include "mozilla/Printf.h"
#include "mozilla/ProfileBufferChunkManagerSingle.h"
#include "mozilla/ProfileBufferChunkManagerWithLocalLimit.h"
#include "mozilla/ProfileChunkedBuffer.h"
#include "mozilla/Services.h"
#include "mozilla/Span.h"
#include "mozilla/StackWalk.h"
#ifdef XP_WIN
# include "mozilla/StackWalkThread.h"
#include "mozilla/StaticPtr.h"
#include "mozilla/ThreadLocal.h"
#include "mozilla/TimeStamp.h"
#include "mozilla/Tuple.h"
#include "mozilla/UniquePtr.h"
#include "mozilla/Vector.h"
#include "prdtoa.h"
#include "prtime.h"
#include "BaseProfiler.h"
#include "BaseProfilingCategory.h"
#include "PageInformation.h"
#include "ProfiledThreadData.h"
#include "ProfilerBacktrace.h"
#include "ProfileBuffer.h"
#include "RegisteredThread.h"
#include "BaseProfilerSharedLibraries.h"
#include "ThreadInfo.h"
#include "VTuneProfiler.h"
// Win32 builds always have frame pointers, so FramePointerStackWalk() always
// works.
#if defined(GP_PLAT_x86_windows)
// Win64 builds always omit frame pointers, so we use the slower
// MozStackWalk(), which works in that case.
#if defined(GP_PLAT_amd64_windows)
// AArch64 Win64 doesn't seem to use frame pointers, so we use the slower
// MozStackWalk().
#if defined(GP_PLAT_arm64_windows)
// Mac builds only have frame pointers when MOZ_PROFILING is specified, so
// FramePointerStackWalk() only works in that case. We don't use MozStackWalk()
// on Mac.
#if defined(GP_OS_darwin) && defined(MOZ_PROFILING)
// No stack-walking in baseprofiler on linux, android, bsd.
// APIs now make it easier to capture backtraces from the Base Profiler, which
// is currently not supported on these platform, and would lead to a MOZ_CRASH
// in Registers::SyncPopulate(). `#if 0` added in bug 1658232, follow-up bugs
// should be referenced in meta bug 1557568.
#if 0
// Android builds use the ARM Exception Handling ABI to unwind.
# if defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
# include "EHABIStackWalk.h"
# endif
// Linux/BSD builds use LUL, which uses DWARF info to unwind stacks.
# if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_x86_linux) || \
defined(GP_PLAT_amd64_android) || defined(GP_PLAT_x86_android) || \
defined(GP_PLAT_mips64_linux) || defined(GP_PLAT_arm64_linux) || \
defined(GP_PLAT_arm64_android) || defined(GP_PLAT_amd64_freebsd) || \
# include "lul/LulMain.h"
# include "lul/platform-linux-lul.h"
// On linux we use LUL for periodic samples and synchronous samples, but we use
// FramePointerStackWalk for backtrace samples when MOZ_PROFILING is enabled.
// (See the comment at the top of the file for a definition of
// periodic/synchronous/backtrace.).
// FramePointerStackWalk can produce incomplete stacks when the current entry is
// in a shared library without framepointers, however LUL can take a long time
// to initialize, which is undesirable for consumers of
// profiler_suspend_and_sample_thread like the Background Hang Reporter.
# if defined(MOZ_PROFILING)
# endif
# endif
// We can only stackwalk without expensive initialization on platforms which
// support FramePointerStackWalk or MozStackWalk. LUL Stackwalking requires
// initializing LUL, and EHABIStackWalk requires initializing EHABI, both of
// which can be expensive.
# include <valgrind/memcheck.h>
# define VALGRIND_MAKE_MEM_DEFINED(_addr, _len) ((void)0)
#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
# include <ucontext.h>
namespace mozilla {
namespace baseprofiler {
using detail::RacyFeatures;
bool LogTest(int aLevelToTest) {
static const int maxLevel = getenv("MOZ_BASE_PROFILER_VERBOSE_LOGGING") ? 5
: 0;
return aLevelToTest <= maxLevel;
void PrintToConsole(const char* aFmt, ...) {
va_list args;
va_start(args, aFmt);
#if defined(ANDROID)
__android_log_vprint(ANDROID_LOG_INFO, "Gecko", aFmt, args);
vfprintf(stderr, aFmt, args);
constexpr static bool ValidateFeatures() {
int expectedFeatureNumber = 0;
// Feature numbers should start at 0 and increase by 1 each.
#define CHECK_FEATURE(n_, str_, Name_, desc_) \
if ((n_) != expectedFeatureNumber) { \
return false; \
} \
return true;
static_assert(ValidateFeatures(), "Feature list is invalid");
// Return all features that are available on this platform.
static uint32_t AvailableFeatures() {
uint32_t features = 0;
#define ADD_FEATURE(n_, str_, Name_, desc_) \
// Add all the possible features.
// Now remove features not supported on this platform/configuration.
#if !defined(HAVE_NATIVE_UNWIND)
#if !defined(GP_OS_windows)
return features;
// Default features common to all contexts (even if not available).
static uint32_t DefaultFeatures() {
return ProfilerFeature::Java | ProfilerFeature::JS | ProfilerFeature::Leaf |
ProfilerFeature::StackWalk | ProfilerFeature::Threads |
// Extra default features when MOZ_PROFILER_STARTUP is set (even if not
// available).
static uint32_t StartupExtraDefaultFeatures() {
// Enable mainthreadio by default for startup profiles as startup is heavy on
// I/O operations, and main thread I/O is really important to see there.
return ProfilerFeature::MainThreadIO;
// The auto-lock/unlock mutex that guards accesses to CorePS and ActivePS.
// Use `PSAutoLock lock;` to take the lock until the end of the enclosing block.
// External profilers may use this same lock for their own data, but as the lock
// is non-recursive, *only* `f(PSLockRef, ...)` functions below should be
// called, to avoid double-locking.
class MOZ_RAII PSAutoLock {
PSAutoLock() : mLock(gPSMutex) {}
PSAutoLock(const PSAutoLock&) = delete;
void operator=(const PSAutoLock&) = delete;
[[nodiscard]] static bool IsLockedOnCurrentThread() {
return gPSMutex.IsLockedOnCurrentThread();
static detail::BaseProfilerMutex gPSMutex;
detail::BaseProfilerAutoLock mLock;
detail::BaseProfilerMutex PSAutoLock::gPSMutex{"Base Profiler mutex"};
// Only functions that take a PSLockRef arg can access CorePS's and ActivePS's
// fields.
typedef const PSAutoLock& PSLockRef;
#define PS_GET(type_, name_) \
static type_ name_(PSLockRef) { \
MOZ_ASSERT(sInstance); \
return sInstance->m##name_; \
#define PS_GET_LOCKLESS(type_, name_) \
static type_ name_() { \
MOZ_ASSERT(sInstance); \
return sInstance->m##name_; \
#define PS_GET_AND_SET(type_, name_) \
PS_GET(type_, name_) \
static void Set##name_(PSLockRef, type_ a##name_) { \
MOZ_ASSERT(sInstance); \
sInstance->m##name_ = a##name_; \
// All functions in this file can run on multiple threads unless they have an
// NS_IsMainThread() assertion.
// This class contains the profiler's core global state, i.e. that which is
// valid even when the profiler is not active. Most profile operations can't do
// anything useful when this class is not instantiated, so we release-assert
// its non-nullness in all such operations.
// Accesses to CorePS are guarded by gPSMutex. Getters and setters take a
// PSAutoLock reference as an argument as proof that the gPSMutex is currently
// locked. This makes it clear when gPSMutex is locked and helps avoid
// accidental unlocked accesses to global state. There are ways to circumvent
// this mechanism, but please don't do so without *very* good reason and a
// detailed explanation.
// The exceptions to this rule:
// - mProcessStartTime, because it's immutable;
// - each thread's RacyRegisteredThread object is accessible without locking via
// TLSRegisteredThread::RacyRegisteredThread().
class CorePS {
: mProcessStartTime(TimeStamp::ProcessCreation()),
// This needs its own mutex, because it is used concurrently from
// functions guarded by gPSMutex as well as others without safety (e.g.,
// profiler_add_marker). It is *not* used inside the critical section of
// the sampler, because mutexes cannot be used there.
~CorePS() {}
static void Create(PSLockRef aLock) {
sInstance = new CorePS();
static void Destroy(PSLockRef aLock) {
delete sInstance;
sInstance = nullptr;
// Unlike ActivePS::Exists(), CorePS::Exists() can be called without gPSMutex
// being locked. This is because CorePS is instantiated so early on the main
// thread that we don't have to worry about it being racy.
static bool Exists() { return !!sInstance; }
static void AddSizeOf(PSLockRef, MallocSizeOf aMallocSizeOf,
size_t& aProfSize, size_t& aLulSize) {
aProfSize += aMallocSizeOf(sInstance);
for (auto& registeredThread : sInstance->mRegisteredThreads) {
aProfSize += registeredThread->SizeOfIncludingThis(aMallocSizeOf);
for (auto& registeredPage : sInstance->mRegisteredPages) {
aProfSize += registeredPage->SizeOfIncludingThis(aMallocSizeOf);
// Measurement of the following things may be added later if DMD finds it
// is worthwhile:
// - CorePS::mRegisteredThreads itself (its elements' children are
// measured above)
// - CorePS::mRegisteredPages itself (its elements' children are
// measured above)
// - CorePS::mInterposeObserver
#if defined(USE_LUL_STACKWALK)
if (sInstance->mLul) {
aLulSize += sInstance->mLul->SizeOfIncludingThis(aMallocSizeOf);
// No PSLockRef is needed for this field because it's immutable.
PS_GET_LOCKLESS(const TimeStamp&, ProcessStartTime)
// No PSLockRef is needed for this field because it's thread-safe.
PS_GET_LOCKLESS(ProfileChunkedBuffer&, CoreBuffer)
PS_GET(const Vector<UniquePtr<RegisteredThread>>&, RegisteredThreads)
static void AppendRegisteredThread(
PSLockRef, UniquePtr<RegisteredThread>&& aRegisteredThread) {
static void RemoveRegisteredThread(PSLockRef,
RegisteredThread* aRegisteredThread) {
// Remove aRegisteredThread from mRegisteredThreads.
for (UniquePtr<RegisteredThread>& rt : sInstance->mRegisteredThreads) {
if (rt.get() == aRegisteredThread) {
PS_GET(Vector<RefPtr<PageInformation>>&, RegisteredPages)
static void AppendRegisteredPage(PSLockRef,
RefPtr<PageInformation>&& aRegisteredPage) {
struct RegisteredPageComparator {
PageInformation* aA;
bool operator()(PageInformation* aB) const { return aA->Equals(aB); }
auto foundPageIter = std::find_if(
sInstance->mRegisteredPages.begin(), sInstance->mRegisteredPages.end(),
if (foundPageIter != sInstance->mRegisteredPages.end()) {
if ((*foundPageIter)->Url() == "about:blank") {
// When a BrowsingContext is loaded, the first url loaded in it will be
// about:blank, and if the principal matches, the first document loaded
// in it will share an inner window. That's why we should delete the
// intermittent about:blank if they share the inner window.
} else {
// Do not register the same page again.
static void RemoveRegisteredPage(PSLockRef,
uint64_t aRegisteredInnerWindowID) {
// Remove RegisteredPage from mRegisteredPages by given inner window ID.
sInstance->mRegisteredPages.eraseIf([&](const RefPtr<PageInformation>& rd) {
return rd->InnerWindowID() == aRegisteredInnerWindowID;
static void ClearRegisteredPages(PSLockRef) {
PS_GET(const Vector<BaseProfilerCount*>&, Counters)
static void AppendCounter(PSLockRef, BaseProfilerCount* aCounter) {
// we don't own the counter; they may be stored in static objects
static void RemoveCounter(PSLockRef, BaseProfilerCount* aCounter) {
// we may be called to remove a counter after the profiler is stopped or
// late in shutdown.
if (sInstance) {
auto* counter = std::find(sInstance->mCounters.begin(),
sInstance->mCounters.end(), aCounter);
MOZ_RELEASE_ASSERT(counter != sInstance->mCounters.end());
static lul::LUL* Lul(PSLockRef) {
return sInstance->mLul.get();
static void SetLul(PSLockRef, UniquePtr<lul::LUL> aLul) {
sInstance->mLul = std::move(aLul);
PS_GET_AND_SET(const std::string&, ProcessName)
PS_GET_AND_SET(const std::string&, ETLDplus1)
// The singleton instance
static CorePS* sInstance;
// The time that the process started.
const TimeStamp mProcessStartTime;
// The thread-safe blocks-oriented buffer into which all profiling data is
// recorded.
// ActivePS controls the lifetime of the underlying contents buffer: When
// ActivePS does not exist, mCoreBuffer is empty and rejects all reads&writes;
// see ActivePS for further details.
// Note: This needs to live here outside of ActivePS, because some producers
// are indirectly controlled (e.g., by atomic flags) and therefore may still
// attempt to write some data shortly after ActivePS has shutdown and deleted
// the underlying buffer in memory.
ProfileChunkedBuffer mCoreBuffer;
// Info on all the registered threads.
// ThreadIds in mRegisteredThreads are unique.
Vector<UniquePtr<RegisteredThread>> mRegisteredThreads;
// Info on all the registered pages.
// InnerWindowIDs in mRegisteredPages are unique.
Vector<RefPtr<PageInformation>> mRegisteredPages;
// Non-owning pointers to all active counters
Vector<BaseProfilerCount*> mCounters;
// LUL's state. Null prior to the first activation, non-null thereafter.
UniquePtr<lul::LUL> mLul;
// Process name, provided by child process initialization code.
std::string mProcessName;
// Private name, provided by child process initialization code (eTLD+1 in
// fission)
std::string mETLDplus1;
CorePS* CorePS::sInstance = nullptr;
ProfileChunkedBuffer& profiler_get_core_buffer() {
return CorePS::CoreBuffer();
class SamplerThread;
static SamplerThread* NewSamplerThread(PSLockRef aLock, uint32_t aGeneration,
double aInterval, bool aStackWalkEnabled,
bool aNoTimerResolutionChange);
struct LiveProfiledThreadData {
RegisteredThread* mRegisteredThread;
UniquePtr<ProfiledThreadData> mProfiledThreadData;
// The buffer size is provided as a number of "entries", this is their size in
// bytes.
constexpr static uint32_t scBytesPerEntry = 8;
// This class contains the profiler's global state that is valid only when the
// profiler is active. When not instantiated, the profiler is inactive.
// Accesses to ActivePS are guarded by gPSMutex, in much the same fashion as
// CorePS.
class ActivePS {
// We need to decide how many chunks of what size we want to fit in the given
// total maximum capacity for this process, in the (likely) context of
// multiple processes doing the same choice and having an inter-process
// mechanism to control the overal memory limit.
// Minimum chunk size allowed, enough for at least one stack.
constexpr static uint32_t scMinimumChunkSize =
2 * ProfileBufferChunkManager::scExpectedMaximumStackSize;
// Ideally we want at least 2 unreleased chunks to work with (1 current and 1
// next), and 2 released chunks (so that one can be recycled when old, leaving
// one with some data).
constexpr static uint32_t scMinimumNumberOfChunks = 4;
// And we want to limit chunks to a maximum size, which is a compromise
// between:
// - A big size, which helps with reducing the rate of allocations and IPCs.
// - A small size, which helps with equalizing the duration of recorded data
// (as the inter-process controller will discard the oldest chunks in all
// Firefox processes).
constexpr static uint32_t scMaximumChunkSize = 1024 * 1024;
// We should be able to store at least the minimum number of the smallest-
// possible chunks.
constexpr static uint32_t scMinimumBufferSize =
scMinimumNumberOfChunks * scMinimumChunkSize;
constexpr static uint32_t scMinimumBufferEntries =
scMinimumBufferSize / scBytesPerEntry;
// Limit to 2GiB.
constexpr static uint32_t scMaximumBufferSize = 2u * 1024u * 1024u * 1024u;
constexpr static uint32_t scMaximumBufferEntries =
scMaximumBufferSize / scBytesPerEntry;
constexpr static uint32_t ClampToAllowedEntries(uint32_t aEntries) {
if (aEntries <= scMinimumBufferEntries) {
return scMinimumBufferEntries;
if (aEntries >= scMaximumBufferEntries) {
return scMaximumBufferEntries;
return aEntries;
constexpr static uint32_t ChunkSizeForEntries(uint32_t aEntries) {
return uint32_t(std::min(size_t(ClampToAllowedEntries(aEntries)) *
scBytesPerEntry / scMinimumNumberOfChunks,
static uint32_t AdjustFeatures(uint32_t aFeatures, uint32_t aFilterCount) {
// Filter out any features unavailable in this platform/configuration.
aFeatures &= AvailableFeatures();
// Always enable ProfilerFeature::Threads if we have a filter, because
// users sometimes ask to filter by a list of threads but forget to
// explicitly specify ProfilerFeature::Threads.
if (aFilterCount > 0) {
aFeatures |= ProfilerFeature::Threads;
// Some features imply others.
if (aFeatures & ProfilerFeature::FileIOAll) {
aFeatures |= ProfilerFeature::MainThreadIO | ProfilerFeature::FileIO;
} else if (aFeatures & ProfilerFeature::FileIO) {
aFeatures |= ProfilerFeature::MainThreadIO;
return aFeatures;
ActivePS(PSLockRef aLock, PowerOfTwo32 aCapacity, double aInterval,
uint32_t aFeatures, const char** aFilters, uint32_t aFilterCount,
const Maybe<double>& aDuration)
: mGeneration(sNextGeneration++),
mFeatures(AdjustFeatures(aFeatures, aFilterCount)),
size_t(ClampToAllowedEntries(aCapacity.Value())) * scBytesPerEntry,
mProfileBuffer([this]() -> ProfileChunkedBuffer& {
return CorePS::CoreBuffer();
// The new sampler thread doesn't start sampling immediately because the
// main loop within Run() is blocked until this function's caller
// unlocks gPSMutex.
aLock, mGeneration, aInterval,
#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
// Deep copy and lower-case aFilters.
for (uint32_t i = 0; i < aFilterCount; ++i) {
mFilters[i] = aFilters[i];
std::transform(mFilters[i].cbegin(), mFilters[i].cend(),
std::back_inserter(mFiltersLowered[i]), ::tolower);
~ActivePS() { CorePS::CoreBuffer().ResetChunkManager(); }
bool ThreadSelected(const char* aThreadName) {
if (mFiltersLowered.empty()) {
return true;
std::string name = aThreadName;
std::transform(name.begin(), name.end(), name.begin(), ::tolower);
for (const auto& filter : mFiltersLowered) {
if (filter == "*") {
return true;
// Crude, non UTF-8 compatible, case insensitive substring search
if (name.find(filter) != std::string::npos) {
return true;
// If the filter starts with pid:, check for a pid match
if (filter.find("pid:") == 0) {
std::string mypid =
if (, std::string::npos, mypid) == 0) {
return true;
return false;
static void Create(PSLockRef aLock, PowerOfTwo32 aCapacity, double aInterval,
uint32_t aFeatures, const char** aFilters,
uint32_t aFilterCount, const Maybe<double>& aDuration) {
sInstance = new ActivePS(aLock, aCapacity, aInterval, aFeatures, aFilters,
aFilterCount, aDuration);
[[nodiscard]] static SamplerThread* Destroy(PSLockRef aLock) {
auto samplerThread = sInstance->mSamplerThread;
delete sInstance;
sInstance = nullptr;
return samplerThread;
static bool Exists(PSLockRef) { return !!sInstance; }
static bool Equals(PSLockRef, PowerOfTwo32 aCapacity,
const Maybe<double>& aDuration, double aInterval,
uint32_t aFeatures, const char** aFilters,
uint32_t aFilterCount) {
if (sInstance->mCapacity != aCapacity ||
sInstance->mDuration != aDuration ||
sInstance->mInterval != aInterval ||
sInstance->mFeatures != aFeatures ||
sInstance->mFilters.length() != aFilterCount) {
return false;
for (uint32_t i = 0; i < sInstance->mFilters.length(); ++i) {
if (strcmp(sInstance->mFilters[i].c_str(), aFilters[i]) != 0) {
return false;
return true;
static size_t SizeOf(PSLockRef, MallocSizeOf aMallocSizeOf) {
size_t n = aMallocSizeOf(sInstance);
n += sInstance->mProfileBuffer.SizeOfExcludingThis(aMallocSizeOf);
// Measurement of the following members may be added later if DMD finds it
// is worthwhile:
// - mLiveProfiledThreads (both the array itself, and the contents)
// - mDeadProfiledThreads (both the array itself, and the contents)
return n;
static bool ShouldProfileThread(PSLockRef aLock, ThreadInfo* aInfo) {
return ((aInfo->IsMainThread() || FeatureThreads(aLock)) &&
PS_GET(uint32_t, Generation)
PS_GET(PowerOfTwo32, Capacity)
PS_GET(Maybe<double>, Duration)
PS_GET(double, Interval)
PS_GET(uint32_t, Features)
#define PS_GET_FEATURE(n_, str_, Name_, desc_) \
static bool Feature##Name_(PSLockRef) { \
MOZ_ASSERT(sInstance); \
return ProfilerFeature::Has##Name_(sInstance->mFeatures); \
PS_GET(const Vector<std::string>&, Filters)
PS_GET(const Vector<std::string>&, FiltersLowered)
static void FulfillChunkRequests(PSLockRef) {
static ProfileBuffer& Buffer(PSLockRef) {
return sInstance->mProfileBuffer;
static const Vector<LiveProfiledThreadData>& LiveProfiledThreads(PSLockRef) {
return sInstance->mLiveProfiledThreads;
// Returns an array containing (RegisteredThread*, ProfiledThreadData*) pairs
// for all threads that should be included in a profile, both for threads
// that are still registered, and for threads that have been unregistered but
// still have data in the buffer.
// For threads that have already been unregistered, the RegisteredThread
// pointer will be null.
// The returned array is sorted by thread register time.
// Do not hold on to the return value across thread registration or profiler
// restarts.
static Vector<std::pair<RegisteredThread*, ProfiledThreadData*>>
ProfiledThreads(PSLockRef) {
Vector<std::pair<RegisteredThread*, ProfiledThreadData*>> array;
array.initCapacity(sInstance->mLiveProfiledThreads.length() +
for (auto& t : sInstance->mLiveProfiledThreads) {
std::make_pair(t.mRegisteredThread, t.mProfiledThreadData.get())));
for (auto& t : sInstance->mDeadProfiledThreads) {
array.append(std::make_pair((RegisteredThread*)nullptr, t.get())));
std::sort(array.begin(), array.end(),
[](const std::pair<RegisteredThread*, ProfiledThreadData*>& a,
const std::pair<RegisteredThread*, ProfiledThreadData*>& b) {
return a.second->Info()->RegisterTime() <
return array;
static Vector<RefPtr<PageInformation>> ProfiledPages(PSLockRef aLock) {
Vector<RefPtr<PageInformation>> array;
for (auto& d : CorePS::RegisteredPages(aLock)) {
for (auto& d : sInstance->mDeadProfiledPages) {
// We don't need to sort the pages like threads since we won't show them
// as a list.
return array;
// Do a linear search through mLiveProfiledThreads to find the
// ProfiledThreadData object for a RegisteredThread.
static ProfiledThreadData* GetProfiledThreadData(
PSLockRef, RegisteredThread* aRegisteredThread) {
for (const LiveProfiledThreadData& thread :
sInstance->mLiveProfiledThreads) {
if (thread.mRegisteredThread == aRegisteredThread) {
return thread.mProfiledThreadData.get();
return nullptr;
static ProfiledThreadData* AddLiveProfiledThread(
PSLockRef, RegisteredThread* aRegisteredThread,
UniquePtr<ProfiledThreadData>&& aProfiledThreadData) {
aRegisteredThread, std::move(aProfiledThreadData)}));
// Return a weak pointer to the ProfiledThreadData object.
return sInstance->mLiveProfiledThreads.back().mProfiledThreadData.get();
static void UnregisterThread(PSLockRef aLockRef,
RegisteredThread* aRegisteredThread) {
// Find the right entry in the mLiveProfiledThreads array and remove the
// element, moving the ProfiledThreadData object for the thread into the
// mDeadProfiledThreads array.
// The thread's RegisteredThread object gets destroyed here.
for (size_t i = 0; i < sInstance->mLiveProfiledThreads.length(); i++) {
LiveProfiledThreadData& thread = sInstance->mLiveProfiledThreads[i];
if (thread.mRegisteredThread == aRegisteredThread) {
PS_GET_AND_SET(bool, IsPaused)
// True if sampling is paused (though generic `SetIsPaused()` or specific
// `SetIsSamplingPaused()`).
static bool IsSamplingPaused(PSLockRef lock) {
return IsPaused(lock) || sInstance->mIsSamplingPaused;
static void SetIsSamplingPaused(PSLockRef, bool aIsSamplingPaused) {
sInstance->mIsSamplingPaused = aIsSamplingPaused;
#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
PS_GET_AND_SET(bool, WasSamplingPaused)
static void DiscardExpiredDeadProfiledThreads(PSLockRef) {
uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
// Discard any dead threads that were unregistered before bufferRangeStart.
const UniquePtr<ProfiledThreadData>& aProfiledThreadData) {
Maybe<uint64_t> bufferPosition =
"should have unregistered this thread");
return *bufferPosition < bufferRangeStart;
static void UnregisterPage(PSLockRef aLock,
uint64_t aRegisteredInnerWindowID) {
auto& registeredPages = CorePS::RegisteredPages(aLock);
for (size_t i = 0; i < registeredPages.length(); i++) {
RefPtr<PageInformation>& page = registeredPages[i];
if (page->InnerWindowID() == aRegisteredInnerWindowID) {
static void DiscardExpiredPages(PSLockRef) {
uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
// Discard any dead pages that were unregistered before
// bufferRangeStart.
[bufferRangeStart](const RefPtr<PageInformation>& aProfiledPage) {
Maybe<uint64_t> bufferPosition =
"should have unregistered this page");
return *bufferPosition < bufferRangeStart;
static void ClearUnregisteredPages(PSLockRef) {
static void ClearExpiredExitProfiles(PSLockRef) {
uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
// Discard exit profiles that were gathered before our buffer RangeStart.
[bufferRangeStart](const ExitProfile& aExitProfile) {
return aExitProfile.mBufferPositionAtGatherTime < bufferRangeStart;
static void AddExitProfile(PSLockRef aLock, const std::string& aExitProfile) {
ExitProfile{aExitProfile, sInstance->mProfileBuffer.BufferRangeEnd()}));
static Vector<std::string> MoveExitProfiles(PSLockRef aLock) {
Vector<std::string> profiles;
for (auto& profile : sInstance->mExitProfiles) {
return profiles;
// The singleton instance.
static ActivePS* sInstance;
// We need to track activity generations. If we didn't we could have the
// following scenario.
// - profiler_stop() locks gPSMutex, de-instantiates ActivePS, unlocks
// gPSMutex, deletes the SamplerThread (which does a join).
// - profiler_start() runs on a different thread, locks gPSMutex,
// re-instantiates ActivePS, unlocks gPSMutex -- all before the join
// completes.
// - SamplerThread::Run() locks gPSMutex, sees that ActivePS is instantiated,
// and continues as if the start/stop pair didn't occur. Also
// profiler_stop() is stuck, unable to finish.
// By checking ActivePS *and* the generation, we can avoid this scenario.
// sNextGeneration is used to track the next generation number; it is static
// because it must persist across different ActivePS instantiations.
const uint32_t mGeneration;
static uint32_t sNextGeneration;
// The maximum number of 8-byte entries in mProfileBuffer.
const PowerOfTwo32 mCapacity;
// The maximum duration of entries in mProfileBuffer, in seconds.
const Maybe<double> mDuration;
// The interval between samples, measured in milliseconds.
const double mInterval;
// The profile features that are enabled.
const uint32_t mFeatures;
// Substrings of names of threads we want to profile.
Vector<std::string> mFilters;
Vector<std::string> mFiltersLowered;
// The chunk manager used by `mProfileBuffer` below.
ProfileBufferChunkManagerWithLocalLimit mProfileBufferChunkManager;
// The buffer into which all samples are recorded.
ProfileBuffer mProfileBuffer;
// ProfiledThreadData objects for any threads that were profiled at any point
// during this run of the profiler:
// - mLiveProfiledThreads contains all threads that are still registered, and
// - mDeadProfiledThreads contains all threads that have already been
// unregistered but for which there is still data in the profile buffer.
Vector<LiveProfiledThreadData> mLiveProfiledThreads;
Vector<UniquePtr<ProfiledThreadData>> mDeadProfiledThreads;
// Info on all the dead pages.
// Registered pages are being moved to this array after unregistration.
// We are keeping them in case we need them in the profile data.
// We are removing them when we ensure that we won't need them anymore.
Vector<RefPtr<PageInformation>> mDeadProfiledPages;
// The current sampler thread. This class is not responsible for destroying
// the SamplerThread object; the Destroy() method returns it so the caller
// can destroy it.
SamplerThread* const mSamplerThread;
// Is the profiler fully paused?
bool mIsPaused;
// Is the profiler periodic sampling paused?
bool mIsSamplingPaused;
#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
// Used to record whether the sampler was paused just before forking. False
// at all times except just before/after forking.
bool mWasSamplingPaused;
struct ExitProfile {
std::string mJSON;
uint64_t mBufferPositionAtGatherTime;
Vector<ExitProfile> mExitProfiles;
ActivePS* ActivePS::sInstance = nullptr;
uint32_t ActivePS::sNextGeneration = 0;
#undef PS_GET
Atomic<uint32_t, MemoryOrdering::Relaxed> RacyFeatures::sActiveAndFeatures(0);
/* static */
void RacyFeatures::SetActive(uint32_t aFeatures) {
sActiveAndFeatures = Active | aFeatures;
/* static */
void RacyFeatures::SetInactive() { sActiveAndFeatures = 0; }
/* static */
bool RacyFeatures::IsActive() { return uint32_t(sActiveAndFeatures) & Active; }
/* static */
void RacyFeatures::SetPaused() { sActiveAndFeatures |= Paused; }
/* static */
void RacyFeatures::SetUnpaused() { sActiveAndFeatures &= ~Paused; }
/* static */
void RacyFeatures::SetSamplingPaused() { sActiveAndFeatures |= SamplingPaused; }
/* static */
void RacyFeatures::SetSamplingUnpaused() {
sActiveAndFeatures &= ~SamplingPaused;
/* static */
bool RacyFeatures::IsActiveWithFeature(uint32_t aFeature) {
uint32_t af = sActiveAndFeatures; // copy it first
return (af & Active) && (af & aFeature);
/* static */
bool RacyFeatures::IsActiveAndUnpaused() {
uint32_t af = sActiveAndFeatures; // copy it first
return (af & Active) && !(af & Paused);
/* static */
bool RacyFeatures::IsActiveAndSamplingUnpaused() {
uint32_t af = sActiveAndFeatures; // copy it first
return (af & Active) && !(af & (Paused | SamplingPaused));
// Each live thread has a RegisteredThread, and we store a reference to it in
// TLS. This class encapsulates that TLS.
class TLSRegisteredThread {
static bool Init(PSLockRef) {
bool ok1 = sRegisteredThread.init();
bool ok2 = AutoProfilerLabel::sProfilingStack.init();
return ok1 && ok2;
// Get the entire RegisteredThread. Accesses are guarded by gPSMutex.
static class RegisteredThread* RegisteredThread(PSLockRef) {
return sRegisteredThread.get();
// Get only the RacyRegisteredThread. Accesses are not guarded by gPSMutex.
static class RacyRegisteredThread* RacyRegisteredThread() {
class RegisteredThread* registeredThread = sRegisteredThread.get();
return registeredThread ? &registeredThread->RacyRegisteredThread()
: nullptr;
// Get only the ProfilingStack. Accesses are not guarded by gPSMutex.
// RacyRegisteredThread() can also be used to get the ProfilingStack, but that
// is marginally slower because it requires an extra pointer indirection.
static ProfilingStack* Stack() {
return AutoProfilerLabel::sProfilingStack.get();
static void SetRegisteredThread(PSLockRef,
class RegisteredThread* aRegisteredThread) {
? &aRegisteredThread->RacyRegisteredThread().ProfilingStack()
: nullptr);
// This is a non-owning reference to the RegisteredThread;
// CorePS::mRegisteredThreads is the owning reference. On thread
// deregistration, this reference is cleared and the RegisteredThread is
// destroyed.
static MOZ_THREAD_LOCAL(class RegisteredThread*) sRegisteredThread;
MOZ_THREAD_LOCAL(RegisteredThread*) TLSRegisteredThread::sRegisteredThread;
/* static */
ProfilingStack* AutoProfilerLabel::GetProfilingStack() {
return sProfilingStack.get();
// Although you can access a thread's ProfilingStack via
// TLSRegisteredThread::sRegisteredThread, we also have a second TLS pointer
// directly to the ProfilingStack. Here's why.
// - We need to be able to push to and pop from the ProfilingStack in
// AutoProfilerLabel.
// - The class functions are hot and must be defined in BaseProfiler.h so they
// can be inlined.
// - We don't want to expose TLSRegisteredThread (and RegisteredThread) in
// BaseProfiler.h.
// This second pointer isn't ideal, but does provide a way to satisfy those
// constraints. TLSRegisteredThread is responsible for updating it.
MOZ_THREAD_LOCAL(ProfilingStack*) AutoProfilerLabel::sProfilingStack;
// The name of the main thread.
static const char* const kMainThreadName = "GeckoMain";
// BEGIN sampling/unwinding code
// The registers used for stack unwinding and a few other sampling purposes.
// The ctor does nothing; users are responsible for filling in the fields.
class Registers {
Registers() : mPC{nullptr}, mSP{nullptr}, mFP{nullptr}, mLR{nullptr} {}
// Fills in mPC, mSP, mFP, mLR, and mContext for a synchronous sample.
void SyncPopulate();
void Clear() { memset(this, 0, sizeof(*this)); }
// These fields are filled in by
// Sampler::SuspendAndSampleAndResumeThread() for periodic and backtrace
// samples, and by SyncPopulate() for synchronous samples.
Address mPC; // Instruction pointer.
Address mSP; // Stack pointer.
Address mFP; // Frame pointer.
Address mLR; // ARM link register.
#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
// This contains all the registers, which means it duplicates the four fields
// above. This is ok.
ucontext_t* mContext; // The context from the signal handler.
// Setting MAX_NATIVE_FRAMES too high risks the unwinder wasting a lot of time
// looping on corrupted stacks.
static const size_t MAX_NATIVE_FRAMES = 1024;
struct NativeStack {
size_t mCount; // Number of frames filled.
NativeStack() : mPCs(), mSPs(), mCount(0) {}
// Merges the profiling stack and native stack, outputting the details to
// aCollector.
static void MergeStacks(uint32_t aFeatures, bool aIsSynchronous,
const RegisteredThread& aRegisteredThread,
const Registers& aRegs, const NativeStack& aNativeStack,
ProfilerStackCollector& aCollector) {
// WARNING: this function runs within the profiler's "critical section".
// WARNING: this function might be called while the profiler is inactive, and
// cannot rely on ActivePS.
const ProfilingStack& profilingStack =
const ProfilingStackFrame* profilingStackFrames = profilingStack.frames;
uint32_t profilingStackFrameCount = profilingStack.stackSize();
Maybe<uint64_t> samplePosInBuffer;
if (!aIsSynchronous) {
// aCollector.SamplePositionInBuffer() will return Nothing() when
// profiler_suspend_and_sample_thread is called from the background hang
// reporter.
samplePosInBuffer = aCollector.SamplePositionInBuffer();
// While the profiling stack array is ordered oldest-to-youngest, the JS and
// native arrays are ordered youngest-to-oldest. We must add frames to aInfo
// oldest-to-youngest. Thus, iterate over the profiling stack forwards and JS
// and native arrays backwards. Note: this means the terminating condition
// jsIndex and nativeIndex is being < 0.
uint32_t profilingStackIndex = 0;
int32_t nativeIndex = aNativeStack.mCount - 1;
uint8_t* lastLabelFrameStackAddr = nullptr;
// Iterate as long as there is at least one frame remaining.
while (profilingStackIndex != profilingStackFrameCount || nativeIndex >= 0) {
// There are 1 to 3 frames available. Find and add the oldest.
uint8_t* profilingStackAddr = nullptr;
uint8_t* nativeStackAddr = nullptr;
if (profilingStackIndex != profilingStackFrameCount) {
const ProfilingStackFrame& profilingStackFrame =
if (profilingStackFrame.isLabelFrame() ||
profilingStackFrame.isSpMarkerFrame()) {
lastLabelFrameStackAddr = (uint8_t*)profilingStackFrame.stackAddress();
// Skip any JS_OSR frames. Such frames are used when the JS interpreter
// enters a jit frame on a loop edge (via on-stack-replacement, or OSR).
// To avoid both the profiling stack frame and jit frame being recorded
// (and showing up twice), the interpreter marks the interpreter
// profiling stack frame as JS_OSR to ensure that it doesn't get counted.
if (profilingStackFrame.isOSRFrame()) {
profilingStackAddr = lastLabelFrameStackAddr;
if (nativeIndex >= 0) {
nativeStackAddr = (uint8_t*)aNativeStack.mSPs[nativeIndex];
// If there's a native stack frame which has the same SP as a profiling
// stack frame, pretend we didn't see the native stack frame. Ditto for a
// native stack frame which has the same SP as a JS stack frame. In effect
// this means profiling stack frames or JS frames trump conflicting native
// frames.
if (nativeStackAddr && (profilingStackAddr == nativeStackAddr)) {
nativeStackAddr = nullptr;
// Sanity checks.
MOZ_ASSERT_IF(profilingStackAddr, profilingStackAddr != nativeStackAddr);
MOZ_ASSERT_IF(nativeStackAddr, nativeStackAddr != profilingStackAddr);
// Check to see if profiling stack frame is top-most.
if (profilingStackAddr > nativeStackAddr) {
MOZ_ASSERT(profilingStackIndex < profilingStackFrameCount);
const ProfilingStackFrame& profilingStackFrame =
// Sp marker frames are just annotations and should not be recorded in
// the profile.
if (!profilingStackFrame.isSpMarkerFrame()) {
if (aIsSynchronous && profilingStackFrame.categoryPair() ==
ProfilingCategoryPair::PROFILER) {
// For stacks captured synchronously (ie. marker stacks), stop
// walking the stack as soon as we enter the profiler category,
// to avoid showing profiler internal code in marker stacks.
// If we reach here, there must be a native stack frame and it must be the
// greatest frame.
if (nativeStackAddr) {
MOZ_ASSERT(nativeIndex >= 0);
void* addr = (void*)aNativeStack.mPCs[nativeIndex];
if (nativeIndex >= 0) {
#if defined(GP_OS_windows) && defined(USE_MOZ_STACK_WALK)
static HANDLE GetThreadHandle(PlatformData* aData);
static void StackWalkCallback(uint32_t aFrameNumber, void* aPC, void* aSP,
void* aClosure) {
NativeStack* nativeStack = static_cast<NativeStack*>(aClosure);
MOZ_ASSERT(nativeStack->mCount < MAX_NATIVE_FRAMES);
nativeStack->mSPs[nativeStack->mCount] = aSP;
nativeStack->mPCs[nativeStack->mCount] = aPC;
static void DoFramePointerBacktrace(PSLockRef aLock,
const RegisteredThread& aRegisteredThread,
const Registers& aRegs,
NativeStack& aNativeStack) {
// WARNING: this function runs within the profiler's "critical section".
// WARNING: this function might be called while the profiler is inactive, and
// cannot rely on ActivePS.
// Start with the current function. We use 0 as the frame number here because
// the FramePointerStackWalk() call below will use 1..N. This is a bit weird
// but it doesn't matter because StackWalkCallback() doesn't use the frame
// number argument.
StackWalkCallback(/* frameNum */ 0, aRegs.mPC, aRegs.mSP, &aNativeStack);
uint32_t maxFrames = uint32_t(MAX_NATIVE_FRAMES - aNativeStack.mCount);
const void* stackEnd = aRegisteredThread.StackTop();
if (aRegs.mFP >= aRegs.mSP && aRegs.mFP <= stackEnd) {
FramePointerStackWalk(StackWalkCallback, maxFrames, &aNativeStack,
#if defined(USE_MOZ_STACK_WALK)
static void DoMozStackWalkBacktrace(PSLockRef aLock,
const RegisteredThread& aRegisteredThread,
const Registers& aRegs,
NativeStack& aNativeStack) {
// WARNING: this function runs within the profiler's "critical section".
// WARNING: this function might be called while the profiler is inactive, and
// cannot rely on ActivePS.
// Start with the current function. We use 0 as the frame number here because
// the MozStackWalkThread() call below will use 1..N. This is a bit weird but
// it doesn't matter because StackWalkCallback() doesn't use the frame number
// argument.
StackWalkCallback(/* frameNum */ 0, aRegs.mPC, aRegs.mSP, &aNativeStack);
uint32_t maxFrames = uint32_t(MAX_NATIVE_FRAMES - aNativeStack.mCount);
HANDLE thread = GetThreadHandle(aRegisteredThread.GetPlatformData());
MozStackWalkThread(StackWalkCallback, maxFrames, &aNativeStack, thread,
/* context */ nullptr);
static void DoEHABIBacktrace(PSLockRef aLock,
const RegisteredThread& aRegisteredThread,
const Registers& aRegs,
NativeStack& aNativeStack) {
// WARNING: this function runs within the profiler's "critical section".
// WARNING: this function might be called while the profiler is inactive, and
// cannot rely on ActivePS.
aNativeStack.mCount =
aNativeStack.mSPs, aNativeStack.mPCs, MAX_NATIVE_FRAMES);
// See the comment at the callsite for why this function is necessary.
MOZ_ASAN_BLACKLIST static void ASAN_memcpy(void* aDst, const void* aSrc,
size_t aLen) {
// The obvious thing to do here is call memcpy(). However, although
// ASAN_memcpy() is not instrumented by ASAN, memcpy() still is, and the
// false positive still manifests! So we must implement memcpy() ourselves
// within this function.
char* dst = static_cast<char*>(aDst);
const char* src = static_cast<const char*>(aSrc);
for (size_t i = 0; i < aLen; i++) {
dst[i] = src[i];
# endif
static void DoLULBacktrace(PSLockRef aLock,
const RegisteredThread& aRegisteredThread,
const Registers& aRegs, NativeStack& aNativeStack) {
// WARNING: this function runs within the profiler's "critical section".
// WARNING: this function might be called while the profiler is inactive, and
// cannot rely on ActivePS.
const mcontext_t* mc = &aRegs.mContext->uc_mcontext;
lul::UnwindRegs startRegs;
memset(&startRegs, 0, sizeof(startRegs));
# if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_amd64_android)
startRegs.xip = lul::TaggedUWord(mc->gregs[REG_RIP]);
startRegs.xsp = lul::TaggedUWord(mc->gregs[REG_RSP]);
startRegs.xbp = lul::TaggedUWord(mc->gregs[REG_RBP]);
# elif defined(GP_PLAT_amd64_freebsd)
startRegs.xip = lul::TaggedUWord(mc->mc_rip);
startRegs.xsp = lul::TaggedUWord(mc->mc_rsp);
startRegs.xbp = lul::TaggedUWord(mc->mc_rbp);
# elif defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
startRegs.r15 = lul::TaggedUWord(mc->arm_pc);
startRegs.r14 = lul::TaggedUWord(mc->arm_lr);
startRegs.r13 = lul::TaggedUWord(mc->arm_sp);
startRegs.r12 = lul::TaggedUWord(mc->arm_ip);
startRegs.r11 = lul::TaggedUWord(mc->arm_fp);
startRegs.r7 = lul::TaggedUWord(mc->arm_r7);
# elif defined(GP_PLAT_arm64_linux) || defined(GP_PLAT_arm64_android)
startRegs.pc = lul::TaggedUWord(mc->pc);
startRegs.x29 = lul::TaggedUWord(mc->regs[29]);
startRegs.x30 = lul::TaggedUWord(mc->regs[30]);
startRegs.sp = lul::TaggedUWord(mc->sp);
# elif defined(GP_PLAT_arm64_freebsd)
startRegs.pc = lul::TaggedUWord(mc->mc_gpregs.gp_elr);
startRegs.x29 = lul::TaggedUWord(mc->mc_gpregs.gp_x[29]);
startRegs.x30 = lul::TaggedUWord(mc->mc_gpregs.gp_lr);
startRegs.sp = lul::TaggedUWord(mc->mc_gpregs.gp_sp);
# elif defined(GP_PLAT_x86_linux) || defined(GP_PLAT_x86_android)
startRegs.xip = lul::TaggedUWord(mc->gregs[REG_EIP]);
startRegs.xsp = lul::TaggedUWord(mc->gregs[REG_ESP]);
startRegs.xbp = lul::TaggedUWord(mc->gregs[REG_EBP]);
# elif defined(GP_PLAT_mips64_linux)
startRegs.pc = lul::TaggedUWord(mc->pc);
startRegs.sp = lul::TaggedUWord(mc->gregs[29]);
startRegs.fp = lul::TaggedUWord(mc->gregs[30]);
# else
# error "Unknown plat"
# endif
// Copy up to N_STACK_BYTES from rsp-REDZONE upwards, but not going past the
// stack's registered top point. Do some basic sanity checks too. This
// assumes that the TaggedUWord holding the stack pointer value is valid, but
// it should be, since it was constructed that way in the code just above.
// We could construct |stackImg| so that LUL reads directly from the stack in
// question, rather than from a copy of it. That would reduce overhead and
// space use a bit. However, it gives a problem with dynamic analysis tools
// (ASan, TSan, Valgrind) which is that such tools will report invalid or
// racing memory accesses, and such accesses will be reported deep inside LUL.
// By taking a copy here, we can either sanitise the copy (for Valgrind) or
// copy it using an unchecked memcpy (for ASan, TSan). That way we don't have
// to try and suppress errors inside LUL.
// N_STACK_BYTES is set to 160KB. This is big enough to hold all stacks
// observed in some minutes of testing, whilst keeping the size of this
// function (DoNativeBacktrace)'s frame reasonable. Most stacks observed in
// practice are small, 4KB or less, and so the copy costs are insignificant
// compared to other profiler overhead.
// |stackImg| is allocated on this (the sampling thread's) stack. That
// implies that the frame for this function is at least N_STACK_BYTES large.
// In general it would be considered unacceptable to have such a large frame
// on a stack, but it only exists for the unwinder thread, and so is not
// expected to be a problem. Allocating it on the heap is troublesome because
// this function runs whilst the sampled thread is suspended, so any heap
// allocation risks deadlock. Allocating it as a global variable is not
// thread safe, which would be a problem if we ever allow multiple sampler
// threads. Hence allocating it on the stack seems to be the least-worst
// option.
lul::StackImage stackImg;
# if defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_amd64_android) || \
uintptr_t rEDZONE_SIZE = 128;
uintptr_t start = startRegs.xsp.Value() - rEDZONE_SIZE;
# elif defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
uintptr_t rEDZONE_SIZE = 0;
uintptr_t start = startRegs.r13.Value() - rEDZONE_SIZE;
# elif defined(GP_PLAT_arm64_linux) || defined(GP_PLAT_arm64_android) || \
uintptr_t rEDZONE_SIZE = 0;
uintptr_t start = startRegs.sp.Value() - rEDZONE_SIZE;
# elif defined(GP_PLAT_x86_linux) || defined(GP_PLAT_x86_android)
uintptr_t rEDZONE_SIZE = 0;
uintptr_t start = startRegs.xsp.Value() - rEDZONE_SIZE;
# elif defined(GP_PLAT_mips64_linux)
uintptr_t rEDZONE_SIZE = 0;
uintptr_t start = startRegs.sp.Value() - rEDZONE_SIZE;
# else
# error "Unknown plat"
# endif
uintptr_t end = reinterpret_cast<uintptr_t>(aRegisteredThread.StackTop());
uintptr_t ws = sizeof(void*);
start &= ~(ws - 1);
end &= ~(ws - 1);
uintptr_t nToCopy = 0;
if (start < end) {
nToCopy = end - start;
if (nToCopy > lul::N_STACK_BYTES) nToCopy = lul::N_STACK_BYTES;
stackImg.mLen = nToCopy;
stackImg.mStartAvma = start;
if (nToCopy > 0) {
// If this is a vanilla memcpy(), ASAN makes the following complaint:
// ERROR: AddressSanitizer: stack-buffer-underflow ...
// ...
// HINT: this may be a false positive if your program uses some custom
// stack unwind mechanism or swapcontext
// This code is very much a custom stack unwind mechanism! So we use an
// alternative memcpy() implementation that is ignored by ASAN.
ASAN_memcpy(&stackImg.mContents[0], (void*)start, nToCopy);
# else
memcpy(&stackImg.mContents[0], (void*)start, nToCopy);
# endif
(void)VALGRIND_MAKE_MEM_DEFINED(&stackImg.mContents[0], nToCopy);
size_t framePointerFramesAcquired = 0;
lul::LUL* lul = CorePS::Lul(aLock);
&aNativeStack.mCount, &framePointerFramesAcquired,
MAX_NATIVE_FRAMES, &startRegs, &stackImg);