Adding upstream version 110.0.1.upstream/110.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 637 insertions, 0 deletions

diff --git a/tools/profiler/core/platform-linux-android.cpp b/tools/profiler/core/platform-linux-android.cpp
new file mode 100644
index 0000000000..3bfe36ffc8
--- /dev/null
+++ b/tools/profiler/core/platform-linux-android.cpp
@@ -0,0 +1,637 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+// Copyright (c) 2006-2011 The Chromium Authors. All rights reserved.
+//
+// Redistribution and use in source and binary forms, with or without
+// modification, are permitted provided that the following conditions
+// are met:
+//  * Redistributions of source code must retain the above copyright
+//    notice, this list of conditions and the following disclaimer.
+//  * Redistributions in binary form must reproduce the above copyright
+//    notice, this list of conditions and the following disclaimer in
+//    the documentation and/or other materials provided with the
+//    distribution.
+//  * Neither the name of Google, Inc. nor the names of its contributors
+//    may be used to endorse or promote products derived from this
+//    software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+// FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+// COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+// BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+// OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+// AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+// OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+// OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+// SUCH DAMAGE.
+
+// This file is used for both Linux and Android as well as FreeBSD.
+
+#include <stdio.h>
+#include <math.h>
+
+#include <pthread.h>
+#if defined(GP_OS_freebsd)
+#  include <sys/thr.h>
+#endif
+#include <semaphore.h>
+#include <signal.h>
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <sys/syscall.h>
+#include <sys/types.h>
+#include <stdlib.h>
+#include <sched.h>
+#include <ucontext.h>
+// Ubuntu Dapper requires memory pages to be marked as
+// executable. Otherwise, OS raises an exception when executing code
+// in that page.
+#include <sys/types.h>  // mmap & munmap
+#include <sys/mman.h>   // mmap & munmap
+#include <sys/stat.h>   // open
+#include <fcntl.h>      // open
+#include <unistd.h>     // sysconf
+#include <semaphore.h>
+#ifdef __GLIBC__
+#  include <execinfo.h>  // backtrace, backtrace_symbols
+#endif                   // def __GLIBC__
+#include <strings.h>     // index
+#include <errno.h>
+#include <stdarg.h>
+
+#include "prenv.h"
+#include "mozilla/PodOperations.h"
+#include "mozilla/DebugOnly.h"
+#if defined(GP_OS_linux) || defined(GP_OS_android)
+#  include "common/linux/breakpad_getcontext.h"
+#endif
+
+#include <string.h>
+#include <list>
+
+using namespace mozilla;
+
+static void PopulateRegsFromContext(Registers& aRegs, ucontext_t* aContext) {
+  aRegs.mContext = aContext;
+  mcontext_t& mcontext = aContext->uc_mcontext;
+
+  // Extracting the sample from the context is extremely machine dependent.
+#if defined(GP_PLAT_x86_linux) || defined(GP_PLAT_x86_android)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.gregs[REG_EIP]);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.gregs[REG_ESP]);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.gregs[REG_EBP]);
+  aRegs.mLR = 0;
+#elif defined(GP_PLAT_amd64_linux) || defined(GP_PLAT_amd64_android)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.gregs[REG_RIP]);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.gregs[REG_RSP]);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.gregs[REG_RBP]);
+  aRegs.mLR = 0;
+#elif defined(GP_PLAT_amd64_freebsd)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.mc_rip);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.mc_rsp);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.mc_rbp);
+  aRegs.mLR = 0;
+#elif defined(GP_PLAT_arm_linux) || defined(GP_PLAT_arm_android)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.arm_pc);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.arm_sp);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.arm_fp);
+  aRegs.mLR = reinterpret_cast<Address>(mcontext.arm_lr);
+#elif defined(GP_PLAT_arm64_linux) || defined(GP_PLAT_arm64_android)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.pc);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.sp);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.regs[29]);
+  aRegs.mLR = reinterpret_cast<Address>(mcontext.regs[30]);
+#elif defined(GP_PLAT_arm64_freebsd)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.mc_gpregs.gp_elr);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.mc_gpregs.gp_sp);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.mc_gpregs.gp_x[29]);
+  aRegs.mLR = reinterpret_cast<Address>(mcontext.mc_gpregs.gp_lr);
+#elif defined(GP_PLAT_mips64_linux) || defined(GP_PLAT_mips64_android)
+  aRegs.mPC = reinterpret_cast<Address>(mcontext.pc);
+  aRegs.mSP = reinterpret_cast<Address>(mcontext.gregs[29]);
+  aRegs.mFP = reinterpret_cast<Address>(mcontext.gregs[30]);
+
+#else
+#  error "bad platform"
+#endif
+}
+
+#if defined(GP_OS_android)
+#  define SYS_tgkill __NR_tgkill
+#endif
+
+#if defined(GP_OS_linux) || defined(GP_OS_android)
+int tgkill(pid_t tgid, pid_t tid, int signalno) {
+  return syscall(SYS_tgkill, tgid, tid, signalno);
+}
+#endif
+
+#if defined(GP_OS_freebsd)
+#  define tgkill thr_kill2
+#endif
+
+mozilla::profiler::PlatformData::PlatformData(ProfilerThreadId aThreadId) {
+  MOZ_ASSERT(aThreadId == profiler_current_thread_id());
+  if (clockid_t clockid; pthread_getcpuclockid(pthread_self(), &clockid) == 0) {
+    mClockId = Some(clockid);
+  }
+}
+
+mozilla::profiler::PlatformData::~PlatformData() = default;
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN Sampler target specifics
+
+// The only way to reliably interrupt a Linux thread and inspect its register
+// and stack state is by sending a signal to it, and doing the work inside the
+// signal handler.  But we don't want to run much code inside the signal
+// handler, since POSIX severely restricts what we can do in signal handlers.
+// So we use a system of semaphores to suspend the thread and allow the
+// sampler thread to do all the work of unwinding and copying out whatever
+// data it wants.
+//
+// A four-message protocol is used to reliably suspend and later resume the
+// thread to be sampled (the samplee):
+//
+// Sampler (signal sender) thread              Samplee (thread to be sampled)
+//
+// Prepare the SigHandlerCoordinator
+// and point sSigHandlerCoordinator at it
+//
+// send SIGPROF to samplee ------- MSG 1 ----> (enter signal handler)
+// wait(mMessage2)                             Copy register state
+//                                               into sSigHandlerCoordinator
+//                         <------ MSG 2 ----- post(mMessage2)
+// Samplee is now suspended.                   wait(mMessage3)
+//   Examine its stack/register
+//   state at leisure
+//
+// Release samplee:
+//   post(mMessage3)       ------- MSG 3 ----->
+// wait(mMessage4)                              Samplee now resumes.  Tell
+//                                                the sampler that we are done.
+//                         <------ MSG 4 ------ post(mMessage4)
+// Now we know the samplee's signal             (leave signal handler)
+//   handler has finished using
+//   sSigHandlerCoordinator.  We can
+//   safely reuse it for some other thread.
+//
+
+// A type used to coordinate between the sampler (signal sending) thread and
+// the thread currently being sampled (the samplee, which receives the
+// signals).
+//
+// The first message is sent using a SIGPROF signal delivery.  The subsequent
+// three are sent using sem_wait/sem_post pairs.  They are named accordingly
+// in the following struct.
+struct SigHandlerCoordinator {
+  SigHandlerCoordinator() {
+    PodZero(&mUContext);
+    int r = sem_init(&mMessage2, /* pshared */ 0, 0);
+    r |= sem_init(&mMessage3, /* pshared */ 0, 0);
+    r |= sem_init(&mMessage4, /* pshared */ 0, 0);
+    MOZ_ASSERT(r == 0);
+    (void)r;
+  }
+
+  ~SigHandlerCoordinator() {
+    int r = sem_destroy(&mMessage2);
+    r |= sem_destroy(&mMessage3);
+    r |= sem_destroy(&mMessage4);
+    MOZ_ASSERT(r == 0);
+    (void)r;
+  }
+
+  sem_t mMessage2;       // To sampler: "context is in sSigHandlerCoordinator"
+  sem_t mMessage3;       // To samplee: "resume"
+  sem_t mMessage4;       // To sampler: "finished with sSigHandlerCoordinator"
+  ucontext_t mUContext;  // Context at signal
+};
+
+struct SigHandlerCoordinator* Sampler::sSigHandlerCoordinator = nullptr;
+
+static void SigprofHandler(int aSignal, siginfo_t* aInfo, void* aContext) {
+  // Avoid TSan warning about clobbering errno.
+  int savedErrno = errno;
+
+  MOZ_ASSERT(aSignal == SIGPROF);
+  MOZ_ASSERT(Sampler::sSigHandlerCoordinator);
+
+  // By sending us this signal, the sampler thread has sent us message 1 in
+  // the comment above, with the meaning "|sSigHandlerCoordinator| is ready
+  // for use, please copy your register context into it."
+  Sampler::sSigHandlerCoordinator->mUContext =
+      *static_cast<ucontext_t*>(aContext);
+
+  // Send message 2: tell the sampler thread that the context has been copied
+  // into |sSigHandlerCoordinator->mUContext|.  sem_post can never fail by
+  // being interrupted by a signal, so there's no loop around this call.
+  int r = sem_post(&Sampler::sSigHandlerCoordinator->mMessage2);
+  MOZ_ASSERT(r == 0);
+
+  // At this point, the sampler thread assumes we are suspended, so we must
+  // not touch any global state here.
+
+  // Wait for message 3: the sampler thread tells us to resume.
+  while (true) {
+    r = sem_wait(&Sampler::sSigHandlerCoordinator->mMessage3);
+    if (r == -1 && errno == EINTR) {
+      // Interrupted by a signal.  Try again.
+      continue;
+    }
+    // We don't expect any other kind of failure
+    MOZ_ASSERT(r == 0);
+    break;
+  }
+
+  // Send message 4: tell the sampler thread that we are finished accessing
+  // |sSigHandlerCoordinator|.  After this point it is not safe to touch
+  // |sSigHandlerCoordinator|.
+  r = sem_post(&Sampler::sSigHandlerCoordinator->mMessage4);
+  MOZ_ASSERT(r == 0);
+
+  errno = savedErrno;
+}
+
+Sampler::Sampler(PSLockRef aLock)
+    : mMyPid(profiler_current_process_id()),
+      // We don't know what the sampler thread's ID will be until it runs, so
+      // set mSamplerTid to a dummy value and fill it in for real in
+      // SuspendAndSampleAndResumeThread().
+      mSamplerTid{} {
+#if defined(USE_EHABI_STACKWALK)
+  mozilla::EHABIStackWalkInit();
+#endif
+
+  // NOTE: We don't initialize LUL here, instead initializing it in
+  // SamplerThread's constructor. This is because with the
+  // profiler_suspend_and_sample_thread entry point, we want to be able to
+  // sample without waiting for LUL to be initialized.
+
+  // Request profiling signals.
+  struct sigaction sa;
+  sa.sa_sigaction = SigprofHandler;
+  sigemptyset(&sa.sa_mask);
+  sa.sa_flags = SA_RESTART | SA_SIGINFO;
+  if (sigaction(SIGPROF, &sa, &mOldSigprofHandler) != 0) {
+    MOZ_CRASH("Error installing SIGPROF handler in the profiler");
+  }
+}
+
+void Sampler::Disable(PSLockRef aLock) {
+  // Restore old signal handler. This is global state so it's important that
+  // we do it now, while gPSMutex is locked.
+  sigaction(SIGPROF, &mOldSigprofHandler, 0);
+}
+
+static void StreamMetaPlatformSampleUnits(PSLockRef aLock,
+                                          SpliceableJSONWriter& aWriter) {
+  aWriter.StringProperty("threadCPUDelta", "ns");
+}
+
+/* static */
+uint64_t RunningTimes::ConvertRawToJson(uint64_t aRawValue) {
+  return aRawValue;
+}
+
+namespace mozilla::profiler {
+bool GetCpuTimeSinceThreadStartInNs(
+    uint64_t* aResult, const mozilla::profiler::PlatformData& aPlatformData) {
+  Maybe<clockid_t> maybeCid = aPlatformData.GetClockId();
+  if (MOZ_UNLIKELY(!maybeCid)) {
+    return false;
+  }
+
+  timespec t;
+  if (clock_gettime(*maybeCid, &t) != 0) {
+    return false;
+  }
+
+  *aResult = uint64_t(t.tv_sec) * 1'000'000'000u + uint64_t(t.tv_nsec);
+  return true;
+}
+}  // namespace mozilla::profiler
+
+static RunningTimes GetProcessRunningTimesDiff(
+    PSLockRef aLock, RunningTimes& aPreviousRunningTimesToBeUpdated) {
+  AUTO_PROFILER_STATS(GetProcessRunningTimes);
+
+  RunningTimes newRunningTimes;
+  {
+    AUTO_PROFILER_STATS(GetProcessRunningTimes_clock_gettime);
+    if (timespec ts; clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &ts) == 0) {
+      newRunningTimes.SetThreadCPUDelta(uint64_t(ts.tv_sec) * 1'000'000'000u +
+                                        uint64_t(ts.tv_nsec));
+    }
+    newRunningTimes.SetPostMeasurementTimeStamp(TimeStamp::Now());
+  };
+
+  const RunningTimes diff = newRunningTimes - aPreviousRunningTimesToBeUpdated;
+  aPreviousRunningTimesToBeUpdated = newRunningTimes;
+  return diff;
+}
+
+static RunningTimes GetThreadRunningTimesDiff(
+    PSLockRef aLock,
+    ThreadRegistration::UnlockedRWForLockedProfiler& aThreadData) {
+  AUTO_PROFILER_STATS(GetRunningTimes_clock_gettime_thread);
+
+  const mozilla::profiler::PlatformData& platformData =
+      aThreadData.PlatformDataCRef();
+  Maybe<clockid_t> maybeCid = platformData.GetClockId();
+
+  if (MOZ_UNLIKELY(!maybeCid)) {
+    // No clock id -> Nothing to measure apart from the timestamp.
+    RunningTimes emptyRunningTimes;
+    emptyRunningTimes.SetPostMeasurementTimeStamp(TimeStamp::Now());
+    return emptyRunningTimes;
+  }
+
+  const RunningTimes newRunningTimes = GetRunningTimesWithTightTimestamp(
+      [cid = *maybeCid](RunningTimes& aRunningTimes) {
+        AUTO_PROFILER_STATS(GetRunningTimes_clock_gettime);
+        if (timespec ts; clock_gettime(cid, &ts) == 0) {
+          aRunningTimes.ResetThreadCPUDelta(
+              uint64_t(ts.tv_sec) * 1'000'000'000u + uint64_t(ts.tv_nsec));
+        } else {
+          aRunningTimes.ClearThreadCPUDelta();
+        }
+      });
+
+  ProfiledThreadData* profiledThreadData =
+      aThreadData.GetProfiledThreadData(aLock);
+  MOZ_ASSERT(profiledThreadData);
+  RunningTimes& previousRunningTimes =
+      profiledThreadData->PreviousThreadRunningTimesRef();
+  const RunningTimes diff = newRunningTimes - previousRunningTimes;
+  previousRunningTimes = newRunningTimes;
+  return diff;
+}
+
+static void DiscardSuspendedThreadRunningTimes(
+    PSLockRef aLock,
+    ThreadRegistration::UnlockedRWForLockedProfiler& aThreadData) {
+  AUTO_PROFILER_STATS(DiscardSuspendedThreadRunningTimes);
+
+  // On Linux, suspending a thread uses a signal that makes that thread work
+  // to handle it. So we want to discard any added running time since the call
+  // to GetThreadRunningTimesDiff, which is done by overwriting the thread's
+  // PreviousThreadRunningTimesRef() with the current running time now.
+
+  const mozilla::profiler::PlatformData& platformData =
+      aThreadData.PlatformDataCRef();
+  Maybe<clockid_t> maybeCid = platformData.GetClockId();
+
+  if (MOZ_UNLIKELY(!maybeCid)) {
+    // No clock id -> Nothing to measure.
+    return;
+  }
+
+  ProfiledThreadData* profiledThreadData =
+      aThreadData.GetProfiledThreadData(aLock);
+  MOZ_ASSERT(profiledThreadData);
+  RunningTimes& previousRunningTimes =
+      profiledThreadData->PreviousThreadRunningTimesRef();
+
+  if (timespec ts; clock_gettime(*maybeCid, &ts) == 0) {
+    previousRunningTimes.ResetThreadCPUDelta(
+        uint64_t(ts.tv_sec) * 1'000'000'000u + uint64_t(ts.tv_nsec));
+  } else {
+    previousRunningTimes.ClearThreadCPUDelta();
+  }
+}
+
+template <typename Func>
+void Sampler::SuspendAndSampleAndResumeThread(
+    PSLockRef aLock,
+    const ThreadRegistration::UnlockedReaderAndAtomicRWOnThread& aThreadData,
+    const TimeStamp& aNow, const Func& aProcessRegs) {
+  // Only one sampler thread can be sampling at once.  So we expect to have
+  // complete control over |sSigHandlerCoordinator|.
+  MOZ_ASSERT(!sSigHandlerCoordinator);
+
+  if (!mSamplerTid.IsSpecified()) {
+    mSamplerTid = profiler_current_thread_id();
+  }
+  ProfilerThreadId sampleeTid = aThreadData.Info().ThreadId();
+  MOZ_RELEASE_ASSERT(sampleeTid != mSamplerTid);
+
+  //----------------------------------------------------------------//
+  // Suspend the samplee thread and get its context.
+
+  SigHandlerCoordinator coord;  // on sampler thread's stack
+  sSigHandlerCoordinator = &coord;
+
+  // Send message 1 to the samplee (the thread to be sampled), by
+  // signalling at it.
+  // This could fail if the thread doesn't exist anymore.
+  int r = tgkill(mMyPid.ToNumber(), sampleeTid.ToNumber(), SIGPROF);
+  if (r == 0) {
+    // Wait for message 2 from the samplee, indicating that the context
+    // is available and that the thread is suspended.
+    while (true) {
+      r = sem_wait(&sSigHandlerCoordinator->mMessage2);
+      if (r == -1 && errno == EINTR) {
+        // Interrupted by a signal.  Try again.
+        continue;
+      }
+      // We don't expect any other kind of failure.
+      MOZ_ASSERT(r == 0);
+      break;
+    }
+
+    //----------------------------------------------------------------//
+    // Sample the target thread.
+
+    // WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
+    //
+    // The profiler's "critical section" begins here.  In the critical section,
+    // we must not do any dynamic memory allocation, nor try to acquire any lock
+    // or any other unshareable resource.  This is because the thread to be
+    // sampled has been suspended at some entirely arbitrary point, and we have
+    // no idea which unsharable resources (locks, essentially) it holds.  So any
+    // attempt to acquire any lock, including the implied locks used by the
+    // malloc implementation, risks deadlock.  This includes TimeStamp::Now(),
+    // which gets a lock on Windows.
+
+    // The samplee thread is now frozen and sSigHandlerCoordinator->mUContext is
+    // valid.  We can poke around in it and unwind its stack as we like.
+
+    // Extract the current register values.
+    Registers regs;
+    PopulateRegsFromContext(regs, &sSigHandlerCoordinator->mUContext);
+    aProcessRegs(regs, aNow);
+
+    //----------------------------------------------------------------//
+    // Resume the target thread.
+
+    // Send message 3 to the samplee, which tells it to resume.
+    r = sem_post(&sSigHandlerCoordinator->mMessage3);
+    MOZ_ASSERT(r == 0);
+
+    // Wait for message 4 from the samplee, which tells us that it has
+    // finished with |sSigHandlerCoordinator|.
+    while (true) {
+      r = sem_wait(&sSigHandlerCoordinator->mMessage4);
+      if (r == -1 && errno == EINTR) {
+        continue;
+      }
+      MOZ_ASSERT(r == 0);
+      break;
+    }
+
+    // The profiler's critical section ends here.  After this point, none of the
+    // critical section limitations documented above apply.
+    //
+    // WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
+  }
+
+  // This isn't strictly necessary, but doing so does help pick up anomalies
+  // in which the signal handler is running when it shouldn't be.
+  sSigHandlerCoordinator = nullptr;
+}
+
+// END Sampler target specifics
+////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN SamplerThread target specifics
+
+static void* ThreadEntry(void* aArg) {
+  auto thread = static_cast<SamplerThread*>(aArg);
+  thread->Run();
+  return nullptr;
+}
+
+SamplerThread::SamplerThread(PSLockRef aLock, uint32_t aActivityGeneration,
+                             double aIntervalMilliseconds, uint32_t aFeatures)
+    : mSampler(aLock),
+      mActivityGeneration(aActivityGeneration),
+      mIntervalMicroseconds(
+          std::max(1, int(floor(aIntervalMilliseconds * 1000 + 0.5)))) {
+#if defined(USE_LUL_STACKWALK)
+  lul::LUL* lul = CorePS::Lul();
+  if (!lul && ProfilerFeature::HasStackWalk(aFeatures)) {
+    CorePS::SetLul(MakeUnique<lul::LUL>(logging_sink_for_LUL));
+    // Read all the unwind info currently available.
+    lul = CorePS::Lul();
+    read_procmaps(lul);
+
+    // Switch into unwind mode. After this point, we can't add or remove any
+    // unwind info to/from this LUL instance. The only thing we can do with
+    // it is Unwind() calls.
+    lul->EnableUnwinding();
+
+    // Has a test been requested?
+    if (PR_GetEnv("MOZ_PROFILER_LUL_TEST")) {
+      int nTests = 0, nTestsPassed = 0;
+      RunLulUnitTests(&nTests, &nTestsPassed, lul);
+    }
+  }
+#endif
+
+  // Start the sampling thread. It repeatedly sends a SIGPROF signal. Sending
+  // the signal ourselves instead of relying on itimer provides much better
+  // accuracy.
+  //
+  // At least 350 KiB of stack space are needed when built with TSAN. This
+  // includes lul::N_STACK_BYTES plus whatever else is needed for the sampler
+  // thread. Set the stack size to 800 KiB to keep a safe margin above that.
+  pthread_attr_t attr;
+  if (pthread_attr_init(&attr) != 0 ||
+      pthread_attr_setstacksize(&attr, 800 * 1024) != 0 ||
+      pthread_create(&mThread, &attr, ThreadEntry, this) != 0) {
+    MOZ_CRASH("pthread_create failed");
+  }
+  pthread_attr_destroy(&attr);
+}
+
+SamplerThread::~SamplerThread() {
+  pthread_join(mThread, nullptr);
+  // Just in the unlikely case some callbacks were added between the end of the
+  // thread and now.
+  InvokePostSamplingCallbacks(std::move(mPostSamplingCallbackList),
+                              SamplingState::JustStopped);
+}
+
+void SamplerThread::SleepMicro(uint32_t aMicroseconds) {
+  if (aMicroseconds >= 1000000) {
+    // Use usleep for larger intervals, because the nanosleep
+    // code below only supports intervals < 1 second.
+    MOZ_ALWAYS_TRUE(!::usleep(aMicroseconds));
+    return;
+  }
+
+  struct timespec ts;
+  ts.tv_sec = 0;
+  ts.tv_nsec = aMicroseconds * 1000UL;
+
+  int rv = ::nanosleep(&ts, &ts);
+
+  while (rv != 0 && errno == EINTR) {
+    // Keep waiting in case of interrupt.
+    // nanosleep puts the remaining time back into ts.
+    rv = ::nanosleep(&ts, &ts);
+  }
+
+  MOZ_ASSERT(!rv, "nanosleep call failed");
+}
+
+void SamplerThread::Stop(PSLockRef aLock) {
+  // Restore old signal handler. This is global state so it's important that
+  // we do it now, while gPSMutex is locked. It's safe to do this now even
+  // though this SamplerThread is still alive, because the next time the main
+  // loop of Run() iterates it won't get past the mActivityGeneration check,
+  // and so won't send any signals.
+  mSampler.Disable(aLock);
+}
+
+// END SamplerThread target specifics
+////////////////////////////////////////////////////////////////////////
+
+#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
+
+// We use pthread_atfork() to temporarily disable signal delivery during any
+// fork() call. Without that, fork() can be repeatedly interrupted by signal
+// delivery, requiring it to be repeatedly restarted, which can lead to *long*
+// delays. See bug 837390.
+//
+// We provide no paf_child() function to run in the child after forking. This
+// is fine because we always immediately exec() after fork(), and exec()
+// clobbers all process state. Also, we don't want the sampler to resume in the
+// child process between fork() and exec(), it would be wasteful.
+//
+// Unfortunately all this is only doable on non-Android because Bionic doesn't
+// have pthread_atfork.
+
+// In the parent, before the fork, increase gSkipSampling to ensure that
+// profiler sampling loops will be skipped. There could be one in progress now,
+// causing a small delay, but further sampling will be skipped, allowing `fork`
+// to complete.
+static void paf_prepare() { ++gSkipSampling; }
+
+// In the parent, after the fork, decrease gSkipSampling to let the sampler
+// resume sampling (unless other places have made it non-zero as well).
+static void paf_parent() { --gSkipSampling; }
+
+static void PlatformInit(PSLockRef aLock) {
+  // Set up the fork handlers.
+  pthread_atfork(paf_prepare, paf_parent, nullptr);
+}
+
+#else
+
+static void PlatformInit(PSLockRef aLock) {}
+
+#endif
+
+#if defined(HAVE_NATIVE_UNWIND)
+void Registers::SyncPopulate() {
+  if (!getcontext(&mContextSyncStorage)) {
+    PopulateRegsFromContext(*this, &mContextSyncStorage);
+  }
+}
+#endif