Adding upstream version 86.0.1.upstream/86.0.1upstream

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

1 files changed, 3712 insertions, 0 deletions

diff --git a/mozglue/baseprofiler/core/platform.cpp b/mozglue/baseprofiler/core/platform.cpp
new file mode 100644
index 0000000000..14c48ce649
--- /dev/null
+++ b/mozglue/baseprofiler/core/platform.cpp
@@ -0,0 +1,3712 @@
+/* -*- 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/. */
+
+// 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"
+#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)
+#  define HAVE_NATIVE_UNWIND
+#  define USE_FRAME_POINTER_STACK_WALK
+#endif
+
+// Win64 builds always omit frame pointers, so we use the slower
+// MozStackWalk(), which works in that case.
+#if defined(GP_PLAT_amd64_windows)
+#  define HAVE_NATIVE_UNWIND
+#  define USE_MOZ_STACK_WALK
+#endif
+
+// AArch64 Win64 doesn't seem to use frame pointers, so we use the slower
+// MozStackWalk().
+#if defined(GP_PLAT_arm64_windows)
+#  define HAVE_NATIVE_UNWIND
+#  define USE_MOZ_STACK_WALK
+#endif
+
+// 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)
+#  define HAVE_NATIVE_UNWIND
+#  define USE_FRAME_POINTER_STACK_WALK
+#endif
+
+// 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)
+#    define HAVE_NATIVE_UNWIND
+#    define USE_EHABI_STACKWALK
+#    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) || \
+      defined(GP_PLAT_arm64_freebsd)
+#    define HAVE_NATIVE_UNWIND
+#    define USE_LUL_STACKWALK
+#    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)
+#      define USE_FRAME_POINTER_STACK_WALK
+#    endif
+#  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.
+#if defined(USE_FRAME_POINTER_STACK_WALK) || defined(USE_MOZ_STACK_WALK)
+#  define HAVE_FASTINIT_NATIVE_UNWIND
+#endif
+
+#ifdef MOZ_VALGRIND
+#  include <valgrind/memcheck.h>
+#else
+#  define VALGRIND_MAKE_MEM_DEFINED(_addr, _len) ((void)0)
+#endif
+
+#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
+#  include <ucontext.h>
+#endif
+
+namespace mozilla {
+namespace baseprofiler {
+
+using detail::RacyFeatures;
+
+bool LogTest(int aLevelToTest) {
+  static const int maxLevel = getenv("MOZ_BASE_PROFILER_VERBOSE_LOGGING") ? 5
+                              : getenv("MOZ_BASE_PROFILER_DEBUG_LOGGING") ? 4
+                              : getenv("MOZ_BASE_PROFILER_LOGGING")       ? 3
+                                                                          : 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);
+#else
+  vfprintf(stderr, aFmt, args);
+#endif
+  va_end(args);
+}
+
+// Statically initialized to 0, then set once from profiler_init(), which should
+// be called from the main thread before any other use of the profiler.
+int scProfilerMainThreadId;
+
+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;                             \
+  }                                           \
+  ++expectedFeatureNumber;
+
+  BASE_PROFILER_FOR_EACH_FEATURE(CHECK_FEATURE)
+
+#undef CHECK_FEATURE
+
+  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_) \
+  ProfilerFeature::Set##Name_(features);
+
+  // Add all the possible features.
+  BASE_PROFILER_FOR_EACH_FEATURE(ADD_FEATURE)
+
+#undef ADD_FEATURE
+
+  // Now remove features not supported on this platform/configuration.
+  ProfilerFeature::ClearJava(features);
+  ProfilerFeature::ClearJS(features);
+  ProfilerFeature::ClearScreenshots(features);
+#if !defined(HAVE_NATIVE_UNWIND)
+  ProfilerFeature::ClearStackWalk(features);
+#endif
+  ProfilerFeature::ClearTaskTracer(features);
+  ProfilerFeature::ClearJSTracer(features);
+
+  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 CPUUtilization by default for startup profiles as it is useful to
+  // see when startup alternates between CPU intensive tasks and being blocked.
+  // 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::CPUUtilization | ProfilerFeature::MainThreadIO;
+}
+
+class MOZ_RAII PSAutoTryLock;
+
+// 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 {
+ public:
+  PSAutoLock() { gPSMutex.Lock(); }
+
+  ~PSAutoLock() { gPSMutex.Unlock(); }
+
+  PSAutoLock(const PSAutoLock&) = delete;
+  void operator=(const PSAutoLock&) = delete;
+
+  [[nodiscard]] static bool IsLockedOnCurrentThread() {
+    return gPSMutex.IsLockedOnCurrentThread();
+  }
+
+ private:
+  // Allow PSAutoTryLock to access gPSMutex, and to call the following
+  // `PSAutoLock(int)` constructor through `Maybe<const PSAutoLock>::emplace()`.
+  friend class PSAutoTryLock;
+  friend class Maybe<const PSAutoLock>;
+
+  // Special constructor for an already-locked gPSMutex. The `int` parameter is
+  // necessary to distinguish it from the main constructor.
+  explicit PSAutoLock(int) { gPSMutex.AssertCurrentThreadOwns(); }
+
+  static detail::BaseProfilerMutex gPSMutex;
+};
+
+// RAII class that attempts to lock the profiler mutex. Example usage:
+//   PSAutoTryLock tryLock;
+//   if (tryLock.IsLocked()) { locked_foo(tryLock.LockRef()); }
+class MOZ_RAII PSAutoTryLock {
+ public:
+  PSAutoTryLock() {
+    if (PSAutoLock::gPSMutex.TryLock()) {
+      mMaybePSAutoLock.emplace(0);
+    }
+  }
+
+  // Return true if the mutex was aquired and locked.
+  [[nodiscard]] bool IsLocked() const { return mMaybePSAutoLock.isSome(); }
+
+  // Assuming the mutex is locked, return a reference to a `PSAutoLock` for that
+  // mutex, which can be passed as proof-of-lock.
+  [[nodiscard]] const PSAutoLock& LockRef() const {
+    MOZ_ASSERT(IsLocked());
+    return mMaybePSAutoLock.ref();
+  }
+
+ private:
+  // `mMaybePSAutoLock` is `Nothing` if locking failed, otherwise it contains a
+  // `const PSAutoLock` holding the locked mutex, and whose reference may be
+  // passed to functions expecting a proof-of-lock.
+  Maybe<const PSAutoLock> mMaybePSAutoLock;
+};
+
+detail::BaseProfilerMutex PSAutoLock::gPSMutex;
+
+// 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 {
+ private:
+  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.
+        mCoreBuffer(ProfileChunkedBuffer::ThreadSafety::WithMutex)
+#ifdef USE_LUL_STACKWALK
+        ,
+        mLul(nullptr)
+#endif
+  {
+  }
+
+  ~CorePS() {}
+
+ public:
+  static void Create(PSLockRef aLock) {
+    MOZ_ASSERT(!sInstance);
+    sInstance = new CorePS();
+  }
+
+  static void Destroy(PSLockRef aLock) {
+    MOZ_ASSERT(sInstance);
+    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) {
+    MOZ_ASSERT(sInstance);
+
+    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);
+    }
+#endif
+  }
+
+  // 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) {
+    MOZ_ASSERT(sInstance);
+    MOZ_RELEASE_ASSERT(
+        sInstance->mRegisteredThreads.append(std::move(aRegisteredThread)));
+  }
+
+  static void RemoveRegisteredThread(PSLockRef,
+                                     RegisteredThread* aRegisteredThread) {
+    MOZ_ASSERT(sInstance);
+    // Remove aRegisteredThread from mRegisteredThreads.
+    for (UniquePtr<RegisteredThread>& rt : sInstance->mRegisteredThreads) {
+      if (rt.get() == aRegisteredThread) {
+        sInstance->mRegisteredThreads.erase(&rt);
+        return;
+      }
+    }
+  }
+
+  PS_GET(Vector<RefPtr<PageInformation>>&, RegisteredPages)
+
+  static void AppendRegisteredPage(PSLockRef,
+                                   RefPtr<PageInformation>&& aRegisteredPage) {
+    MOZ_ASSERT(sInstance);
+    struct RegisteredPageComparator {
+      PageInformation* aA;
+      bool operator()(PageInformation* aB) const { return aA->Equals(aB); }
+    };
+
+    auto foundPageIter = std::find_if(
+        sInstance->mRegisteredPages.begin(), sInstance->mRegisteredPages.end(),
+        RegisteredPageComparator{aRegisteredPage.get()});
+
+    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.
+        sInstance->mRegisteredPages.erase(foundPageIter);
+      } else {
+        // Do not register the same page again.
+        return;
+      }
+    }
+    MOZ_RELEASE_ASSERT(
+        sInstance->mRegisteredPages.append(std::move(aRegisteredPage)));
+  }
+
+  static void RemoveRegisteredPage(PSLockRef,
+                                   uint64_t aRegisteredInnerWindowID) {
+    MOZ_ASSERT(sInstance);
+    // Remove RegisteredPage from mRegisteredPages by given inner window ID.
+    sInstance->mRegisteredPages.eraseIf([&](const RefPtr<PageInformation>& rd) {
+      return rd->InnerWindowID() == aRegisteredInnerWindowID;
+    });
+  }
+
+  static void ClearRegisteredPages(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    sInstance->mRegisteredPages.clear();
+  }
+
+  PS_GET(const Vector<BaseProfilerCount*>&, Counters)
+
+  static void AppendCounter(PSLockRef, BaseProfilerCount* aCounter) {
+    MOZ_ASSERT(sInstance);
+    // we don't own the counter; they may be stored in static objects
+    MOZ_RELEASE_ASSERT(sInstance->mCounters.append(aCounter));
+  }
+
+  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());
+      sInstance->mCounters.erase(counter);
+    }
+  }
+
+#ifdef USE_LUL_STACKWALK
+  static lul::LUL* Lul(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    return sInstance->mLul.get();
+  }
+  static void SetLul(PSLockRef, UniquePtr<lul::LUL> aLul) {
+    MOZ_ASSERT(sInstance);
+    sInstance->mLul = std::move(aLul);
+  }
+#endif
+
+  PS_GET_AND_SET(const std::string&, ProcessName)
+  PS_GET_AND_SET(const std::string&, ETLDplus1)
+
+ private:
+  // 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;
+
+#ifdef USE_LUL_STACKWALK
+  // LUL's state. Null prior to the first activation, non-null thereafter.
+  UniquePtr<lul::LUL> mLul;
+#endif
+
+  // 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() {
+  MOZ_ASSERT(CorePS::Exists());
+  return CorePS::CoreBuffer();
+}
+
+class SamplerThread;
+
+static SamplerThread* NewSamplerThread(PSLockRef aLock, uint32_t aGeneration,
+                                       double aInterval);
+
+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 {
+ private:
+  // 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;
+
+ public:
+  // 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;
+  }
+
+ private:
+  constexpr static uint32_t ChunkSizeForEntries(uint32_t aEntries) {
+    return uint32_t(std::min(size_t(ClampToAllowedEntries(aEntries)) *
+                                 scBytesPerEntry / scMinimumNumberOfChunks,
+                             size_t(scMaximumChunkSize)));
+  }
+
+  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++),
+        mCapacity(aCapacity),
+        mDuration(aDuration),
+        mInterval(aInterval),
+        mFeatures(AdjustFeatures(aFeatures, aFilterCount)),
+        mProfileBufferChunkManager(
+            size_t(ClampToAllowedEntries(aCapacity.Value())) * scBytesPerEntry,
+            ChunkSizeForEntries(aCapacity.Value())),
+        mProfileBuffer([this]() -> ProfileChunkedBuffer& {
+          CorePS::CoreBuffer().SetChunkManager(mProfileBufferChunkManager);
+          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.
+        mSamplerThread(NewSamplerThread(aLock, mGeneration, aInterval)),
+        mIsPaused(false),
+        mIsSamplingPaused(false)
+#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
+        ,
+        mWasSamplingPaused(false)
+#endif
+  {
+    // Deep copy aFilters.
+    MOZ_ALWAYS_TRUE(mFilters.resize(aFilterCount));
+    for (uint32_t i = 0; i < aFilterCount; ++i) {
+      mFilters[i] = aFilters[i];
+    }
+  }
+
+  ~ActivePS() { CorePS::CoreBuffer().ResetChunkManager(); }
+
+  bool ThreadSelected(const char* aThreadName) {
+    if (mFilters.empty()) {
+      return true;
+    }
+
+    std::string name = aThreadName;
+    std::transform(name.begin(), name.end(), name.begin(), ::tolower);
+
+    for (uint32_t i = 0; i < mFilters.length(); ++i) {
+      std::string filter = mFilters[i];
+
+      if (filter == "*") {
+        return true;
+      }
+
+      std::transform(filter.begin(), filter.end(), filter.begin(), ::tolower);
+
+      // 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 = std::to_string(profiler_current_process_id());
+        if (filter.compare(4, std::string::npos, mypid) == 0) {
+          return true;
+        }
+      }
+    }
+
+    return false;
+  }
+
+ public:
+  static void Create(PSLockRef aLock, PowerOfTwo32 aCapacity, double aInterval,
+                     uint32_t aFeatures, const char** aFilters,
+                     uint32_t aFilterCount, const Maybe<double>& aDuration) {
+    MOZ_ASSERT(!sInstance);
+    sInstance = new ActivePS(aLock, aCapacity, aInterval, aFeatures, aFilters,
+                             aFilterCount, aDuration);
+  }
+
+  [[nodiscard]] static SamplerThread* Destroy(PSLockRef aLock) {
+    MOZ_ASSERT(sInstance);
+    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) {
+    MOZ_ASSERT(sInstance);
+    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) {
+    MOZ_ASSERT(sInstance);
+
+    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) {
+    MOZ_ASSERT(sInstance);
+    return ((aInfo->IsMainThread() || FeatureThreads(aLock)) &&
+            sInstance->ThreadSelected(aInfo->Name()));
+  }
+
+  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); \
+  }
+
+  BASE_PROFILER_FOR_EACH_FEATURE(PS_GET_FEATURE)
+
+#undef PS_GET_FEATURE
+
+  PS_GET(const Vector<std::string>&, Filters)
+
+  static void FulfillChunkRequests(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    sInstance->mProfileBufferChunkManager.FulfillChunkRequests();
+  }
+
+  static ProfileBuffer& Buffer(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    return sInstance->mProfileBuffer;
+  }
+
+  static const Vector<LiveProfiledThreadData>& LiveProfiledThreads(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    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) {
+    MOZ_ASSERT(sInstance);
+    Vector<std::pair<RegisteredThread*, ProfiledThreadData*>> array;
+    MOZ_RELEASE_ASSERT(
+        array.initCapacity(sInstance->mLiveProfiledThreads.length() +
+                           sInstance->mDeadProfiledThreads.length()));
+    for (auto& t : sInstance->mLiveProfiledThreads) {
+      MOZ_RELEASE_ASSERT(array.append(
+          std::make_pair(t.mRegisteredThread, t.mProfiledThreadData.get())));
+    }
+    for (auto& t : sInstance->mDeadProfiledThreads) {
+      MOZ_RELEASE_ASSERT(
+          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() <
+                       b.second->Info()->RegisterTime();
+              });
+    return array;
+  }
+
+  static Vector<RefPtr<PageInformation>> ProfiledPages(PSLockRef aLock) {
+    MOZ_ASSERT(sInstance);
+    Vector<RefPtr<PageInformation>> array;
+    for (auto& d : CorePS::RegisteredPages(aLock)) {
+      MOZ_RELEASE_ASSERT(array.append(d));
+    }
+    for (auto& d : sInstance->mDeadProfiledPages) {
+      MOZ_RELEASE_ASSERT(array.append(d));
+    }
+    // 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) {
+    MOZ_ASSERT(sInstance);
+    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) {
+    MOZ_ASSERT(sInstance);
+    MOZ_RELEASE_ASSERT(
+        sInstance->mLiveProfiledThreads.append(LiveProfiledThreadData{
+            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) {
+    MOZ_ASSERT(sInstance);
+
+    DiscardExpiredDeadProfiledThreads(aLockRef);
+
+    // 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) {
+        thread.mProfiledThreadData->NotifyUnregistered(
+            sInstance->mProfileBuffer.BufferRangeEnd());
+        MOZ_RELEASE_ASSERT(sInstance->mDeadProfiledThreads.append(
+            std::move(thread.mProfiledThreadData)));
+        sInstance->mLiveProfiledThreads.erase(
+            &sInstance->mLiveProfiledThreads[i]);
+        return;
+      }
+    }
+  }
+
+  PS_GET_AND_SET(bool, IsPaused)
+
+  // True if sampling is paused (though generic `SetIsPaused()` or specific
+  // `SetIsSamplingPaused()`).
+  static bool IsSamplingPaused(PSLockRef lock) {
+    MOZ_ASSERT(sInstance);
+    return IsPaused(lock) || sInstance->mIsSamplingPaused;
+  }
+
+  static void SetIsSamplingPaused(PSLockRef, bool aIsSamplingPaused) {
+    MOZ_ASSERT(sInstance);
+    sInstance->mIsSamplingPaused = aIsSamplingPaused;
+  }
+
+#if defined(GP_OS_linux) || defined(GP_OS_freebsd)
+  PS_GET_AND_SET(bool, WasSamplingPaused)
+#endif
+
+  static void DiscardExpiredDeadProfiledThreads(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
+    // Discard any dead threads that were unregistered before bufferRangeStart.
+    sInstance->mDeadProfiledThreads.eraseIf(
+        [bufferRangeStart](
+            const UniquePtr<ProfiledThreadData>& aProfiledThreadData) {
+          Maybe<uint64_t> bufferPosition =
+              aProfiledThreadData->BufferPositionWhenUnregistered();
+          MOZ_RELEASE_ASSERT(bufferPosition,
+                             "should have unregistered this thread");
+          return *bufferPosition < bufferRangeStart;
+        });
+  }
+
+  static void UnregisterPage(PSLockRef aLock,
+                             uint64_t aRegisteredInnerWindowID) {
+    MOZ_ASSERT(sInstance);
+    auto& registeredPages = CorePS::RegisteredPages(aLock);
+    for (size_t i = 0; i < registeredPages.length(); i++) {
+      RefPtr<PageInformation>& page = registeredPages[i];
+      if (page->InnerWindowID() == aRegisteredInnerWindowID) {
+        page->NotifyUnregistered(sInstance->mProfileBuffer.BufferRangeEnd());
+        MOZ_RELEASE_ASSERT(
+            sInstance->mDeadProfiledPages.append(std::move(page)));
+        registeredPages.erase(&registeredPages[i--]);
+      }
+    }
+  }
+
+  static void DiscardExpiredPages(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
+    // Discard any dead pages that were unregistered before
+    // bufferRangeStart.
+    sInstance->mDeadProfiledPages.eraseIf(
+        [bufferRangeStart](const RefPtr<PageInformation>& aProfiledPage) {
+          Maybe<uint64_t> bufferPosition =
+              aProfiledPage->BufferPositionWhenUnregistered();
+          MOZ_RELEASE_ASSERT(bufferPosition,
+                             "should have unregistered this page");
+          return *bufferPosition < bufferRangeStart;
+        });
+  }
+
+  static void ClearUnregisteredPages(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    sInstance->mDeadProfiledPages.clear();
+  }
+
+  static void ClearExpiredExitProfiles(PSLockRef) {
+    MOZ_ASSERT(sInstance);
+    uint64_t bufferRangeStart = sInstance->mProfileBuffer.BufferRangeStart();
+    // Discard exit profiles that were gathered before our buffer RangeStart.
+    sInstance->mExitProfiles.eraseIf(
+        [bufferRangeStart](const ExitProfile& aExitProfile) {
+          return aExitProfile.mBufferPositionAtGatherTime < bufferRangeStart;
+        });
+  }
+
+  static void AddExitProfile(PSLockRef aLock, const std::string& aExitProfile) {
+    MOZ_ASSERT(sInstance);
+
+    ClearExpiredExitProfiles(aLock);
+
+    MOZ_RELEASE_ASSERT(sInstance->mExitProfiles.append(
+        ExitProfile{aExitProfile, sInstance->mProfileBuffer.BufferRangeEnd()}));
+  }
+
+  static Vector<std::string> MoveExitProfiles(PSLockRef aLock) {
+    MOZ_ASSERT(sInstance);
+
+    ClearExpiredExitProfiles(aLock);
+
+    Vector<std::string> profiles;
+    MOZ_RELEASE_ASSERT(
+        profiles.initCapacity(sInstance->mExitProfiles.length()));
+    for (auto& profile : sInstance->mExitProfiles) {
+      MOZ_RELEASE_ASSERT(profiles.append(std::move(profile.mJSON)));
+    }
+    sInstance->mExitProfiles.clear();
+    return profiles;
+  }
+
+ private:
+  // 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;
+
+  // 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;
+#endif
+
+  struct ExitProfile {
+    std::string mJSON;
+    uint64_t mBufferPositionAtGatherTime;
+  };
+  Vector<ExitProfile> mExitProfiles;
+};
+
+ActivePS* ActivePS::sInstance = nullptr;
+uint32_t ActivePS::sNextGeneration = 0;
+
+#undef PS_GET
+#undef PS_GET_LOCKLESS
+#undef PS_GET_AND_SET
+
+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 {
+ public:
+  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) {
+    sRegisteredThread.set(aRegisteredThread);
+    AutoProfilerLabel::sProfilingStack.set(
+        aRegisteredThread
+            ? &aRegisteredThread->RacyRegisteredThread().ProfilingStack()
+            : nullptr);
+  }
+
+ private:
+  // 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 {
+ public:
+  Registers() : mPC{nullptr}, mSP{nullptr}, mFP{nullptr}, mLR{nullptr} {}
+
+#if defined(HAVE_NATIVE_UNWIND)
+  // Fills in mPC, mSP, mFP, mLR, and mContext for a synchronous sample.
+  void SyncPopulate();
+#endif
+
+  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.
+#endif
+};
+
+// 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 {
+  void* mPCs[MAX_NATIVE_FRAMES];
+  void* mSPs[MAX_NATIVE_FRAMES];
+  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 =
+      aRegisteredThread.RacyRegisteredThread().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 =
+          profilingStackFrames[profilingStackIndex];
+
+      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()) {
+        profilingStackIndex++;
+        continue;
+      }
+
+      MOZ_ASSERT(lastLabelFrameStackAddr);
+      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;
+      nativeIndex--;
+      MOZ_ASSERT(profilingStackAddr);
+    }
+
+    // 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 =
+          profilingStackFrames[profilingStackIndex];
+
+      // Sp marker frames are just annotations and should not be recorded in
+      // the profile.
+      if (!profilingStackFrame.isSpMarkerFrame()) {
+        aCollector.CollectProfilingStackFrame(profilingStackFrame);
+      }
+      profilingStackIndex++;
+      continue;
+    }
+
+    // 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];
+      aCollector.CollectNativeLeafAddr(addr);
+    }
+    if (nativeIndex >= 0) {
+      nativeIndex--;
+    }
+  }
+}
+
+#if defined(GP_OS_windows) && defined(USE_MOZ_STACK_WALK)
+static HANDLE GetThreadHandle(PlatformData* aData);
+#endif
+
+#if defined(USE_FRAME_POINTER_STACK_WALK) || defined(USE_MOZ_STACK_WALK)
+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;
+  nativeStack->mCount++;
+}
+#endif
+
+#if defined(USE_FRAME_POINTER_STACK_WALK)
+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, /* skipFrames */ 0, maxFrames,
+                          &aNativeStack, reinterpret_cast<void**>(aRegs.mFP),
+                          const_cast<void*>(stackEnd));
+  }
+}
+#endif
+
+#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());
+  MOZ_ASSERT(thread);
+  MozStackWalkThread(StackWalkCallback, /* skipFrames */ 0, maxFrames,
+                     &aNativeStack, thread, /* context */ nullptr);
+}
+#endif
+
+#ifdef USE_EHABI_STACKWALK
+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 =
+      EHABIStackWalk(aRegs.mContext->uc_mcontext,
+                     const_cast<void*>(aRegisteredThread.StackTop()),
+                     aNativeStack.mSPs, aNativeStack.mPCs, MAX_NATIVE_FRAMES);
+}
+#endif
+
+#ifdef USE_LUL_STACKWALK
+
+// See the comment at the callsite for why this function is necessary.
+#  if defined(MOZ_HAVE_ASAN_BLACKLIST)
+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) || \
+      defined(GP_PLAT_amd64_freebsd)
+    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) || \
+      defined(GP_PLAT_arm64_freebsd)
+    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;
+    }
+    MOZ_ASSERT(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.
+#  if defined(MOZ_HAVE_ASAN_BLACKLIST)
+      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);
+  lul->Unwind(reinterpret_cast<uintptr_t*>(aNativeStack.mPCs),
+              reinterpret_cast<uintptr_t*>(aNativeStack.mSPs),
+              &aNativeStack.mCount, &framePointerFramesAcquired,
+              MAX_NATIVE_FRAMES, &startRegs, &stackImg);
+
+  // Update stats in the LUL stats object.  Unfortunately this requires
+  // three global memory operations.
+  lul->mStats.mContext += 1;
+  lul->mStats.mCFI += aNativeStack.mCount - 1 - framePointerFramesAcquired;
+  lul->mStats.mFP += framePointerFramesAcquired;
+}
+
+#endif
+
+#ifdef HAVE_NATIVE_UNWIND
+static void DoNativeBacktrace(PSLockRef aLock,
+                              const RegisteredThread& aRegisteredThread,
+                              const Registers& aRegs,
+                              NativeStack& aNativeStack) {
+  // This method determines which stackwalker is used for periodic and
+  // synchronous samples. (Backtrace samples are treated differently, see
+  // profiler_suspend_and_sample_thread() for details). The only part of the
+  // ordering that matters is that LUL must precede FRAME_POINTER, because on
+  // Linux they can both be present.
+#  if defined(USE_LUL_STACKWALK)
+  DoLULBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
+#  elif defined(USE_EHABI_STACKWALK)
+  DoEHABIBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
+#  elif defined(USE_FRAME_POINTER_STACK_WALK)
+  DoFramePointerBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
+#  elif defined(USE_MOZ_STACK_WALK)
+  DoMozStackWalkBacktrace(aLock, aRegisteredThread, aRegs, aNativeStack);
+#  else
+#    error "Invalid configuration"
+#  endif
+}
+#endif
+
+// Writes some components shared by periodic and synchronous profiles to
+// ActivePS's ProfileBuffer. (This should only be called from DoSyncSample()
+// and DoPeriodicSample().)
+//
+// The grammar for entry sequences is in a comment above
+// ProfileBuffer::StreamSamplesToJSON.
+static inline void DoSharedSample(PSLockRef aLock, bool aIsSynchronous,
+                                  RegisteredThread& aRegisteredThread,
+                                  const Registers& aRegs, uint64_t aSamplePos,
+                                  ProfileBuffer& aBuffer) {
+  // WARNING: this function runs within the profiler's "critical section".
+
+  MOZ_ASSERT(!aBuffer.IsThreadSafe(),
+             "Mutexes cannot be used inside this critical section");
+
+  MOZ_RELEASE_ASSERT(ActivePS::Exists(aLock));
+
+  ProfileBufferCollector collector(aBuffer, aSamplePos);
+  NativeStack nativeStack;
+#if defined(HAVE_NATIVE_UNWIND)
+  if (ActivePS::FeatureStackWalk(aLock)) {
+    DoNativeBacktrace(aLock, aRegisteredThread, aRegs, nativeStack);
+
+    MergeStacks(ActivePS::Features(aLock), aIsSynchronous, aRegisteredThread,
+                aRegs, nativeStack, collector);
+  } else
+#endif
+  {
+    MergeStacks(ActivePS::Features(aLock), aIsSynchronous, aRegisteredThread,
+                aRegs, nativeStack, collector);
+
+    // We can't walk the whole native stack, but we can record the top frame.
+    if (ActivePS::FeatureLeaf(aLock)) {
+      aBuffer.AddEntry(ProfileBufferEntry::NativeLeafAddr((void*)aRegs.mPC));
+    }
+  }
+}
+
+// Writes the components of a synchronous sample to the given ProfileBuffer.
+static void DoSyncSample(PSLockRef aLock, RegisteredThread& aRegisteredThread,
+                         const TimeStamp& aNow, const Registers& aRegs,
+                         ProfileBuffer& aBuffer) {
+  // WARNING: this function runs within the profiler's "critical section".
+
+  uint64_t samplePos =
+      aBuffer.AddThreadIdEntry(aRegisteredThread.Info()->ThreadId());
+
+  TimeDuration delta = aNow - CorePS::ProcessStartTime();
+  aBuffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));
+
+  DoSharedSample(aLock, /* aIsSynchronous = */ true, aRegisteredThread, aRegs,
+                 samplePos, aBuffer);
+}
+
+// Writes the components of a periodic sample to ActivePS's ProfileBuffer.
+// The ThreadId entry is already written in the main ProfileBuffer, its location
+// is `aSamplePos`, we can write the rest to `aBuffer` (which may be different).
+static void DoPeriodicSample(PSLockRef aLock,
+                             RegisteredThread& aRegisteredThread,
+                             ProfiledThreadData& aProfiledThreadData,
+                             const Registers& aRegs, uint64_t aSamplePos,
+                             ProfileBuffer& aBuffer) {
+  // WARNING: this function runs within the profiler's "critical section".
+
+  DoSharedSample(aLock, /* aIsSynchronous = */ false, aRegisteredThread, aRegs,
+                 aSamplePos, aBuffer);
+}
+
+// END sampling/unwinding code
+////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN saving/streaming code
+
+const static uint64_t kJS_MAX_SAFE_UINTEGER = +9007199254740991ULL;
+
+static int64_t SafeJSInteger(uint64_t aValue) {
+  return aValue <= kJS_MAX_SAFE_UINTEGER ? int64_t(aValue) : -1;
+}
+
+static void AddSharedLibraryInfoToStream(JSONWriter& aWriter,
+                                         const SharedLibrary& aLib) {
+  aWriter.StartObjectElement();
+  aWriter.IntProperty("start", SafeJSInteger(aLib.GetStart()));
+  aWriter.IntProperty("end", SafeJSInteger(aLib.GetEnd()));
+  aWriter.IntProperty("offset", SafeJSInteger(aLib.GetOffset()));
+  aWriter.StringProperty("name", aLib.GetModuleName());
+  aWriter.StringProperty("path", aLib.GetModulePath());
+  aWriter.StringProperty("debugName", aLib.GetDebugName());
+  aWriter.StringProperty("debugPath", aLib.GetDebugPath());
+  aWriter.StringProperty("breakpadId", aLib.GetBreakpadId());
+  aWriter.StringProperty("arch", aLib.GetArch());
+  aWriter.EndObject();
+}
+
+void AppendSharedLibraries(JSONWriter& aWriter) {
+  SharedLibraryInfo info = SharedLibraryInfo::GetInfoForSelf();
+  info.SortByAddress();
+  for (size_t i = 0; i < info.GetSize(); i++) {
+    AddSharedLibraryInfoToStream(aWriter, info.GetEntry(i));
+  }
+}
+
+static void StreamCategories(SpliceableJSONWriter& aWriter) {
+  // Same order as ProfilingCategory. Format:
+  // [
+  //   {
+  //     name: "Idle",
+  //     color: "transparent",
+  //     subcategories: ["Other"],
+  //   },
+  //   {
+  //     name: "Other",
+  //     color: "grey",
+  //     subcategories: [
+  //       "JSM loading",
+  //       "Subprocess launching",
+  //       "DLL loading"
+  //     ]
+  //   },
+  //   ...
+  // ]
+
+#define CATEGORY_JSON_BEGIN_CATEGORY(name, labelAsString, color) \
+  aWriter.Start();                                               \
+  aWriter.StringProperty("name", labelAsString);                 \
+  aWriter.StringProperty("color", color);                        \
+  aWriter.StartArrayProperty("subcategories");
+#define CATEGORY_JSON_SUBCATEGORY(supercategory, name, labelAsString) \
+  aWriter.StringElement(labelAsString);
+#define CATEGORY_JSON_END_CATEGORY \
+  aWriter.EndArray();              \
+  aWriter.EndObject();
+
+  MOZ_PROFILING_CATEGORY_LIST(CATEGORY_JSON_BEGIN_CATEGORY,
+                              CATEGORY_JSON_SUBCATEGORY,
+                              CATEGORY_JSON_END_CATEGORY)
+
+#undef CATEGORY_JSON_BEGIN_CATEGORY
+#undef CATEGORY_JSON_SUBCATEGORY
+#undef CATEGORY_JSON_END_CATEGORY
+}
+
+static void StreamMarkerSchema(SpliceableJSONWriter& aWriter) {
+  // Get an array view with all registered marker-type-specific functions.
+  Span<const base_profiler_markers_detail::Streaming::MarkerTypeFunctions>
+      markerTypeFunctionsArray =
+          base_profiler_markers_detail::Streaming::MarkerTypeFunctionsArray();
+  // List of streamed marker names, this is used to spot duplicates.
+  std::set<std::string> names;
+  // Stream the display schema for each different one. (Duplications may come
+  // from the same code potentially living in different libraries.)
+  for (const auto& markerTypeFunctions : markerTypeFunctionsArray) {
+    auto name = markerTypeFunctions.mMarkerTypeNameFunction();
+    // std::set.insert(T&&) returns a pair, its `second` is true if the element
+    // was actually inserted (i.e., it was not there yet.)
+    const bool didInsert =
+        names.insert(std::string(name.data(), name.size())).second;
+    if (didInsert) {
+      markerTypeFunctions.mMarkerSchemaFunction().Stream(aWriter, name);
+    }
+  }
+}
+
+static int64_t MicrosecondsSince1970();
+
+static void StreamMetaJSCustomObject(PSLockRef aLock,
+                                     SpliceableJSONWriter& aWriter,
+                                     bool aIsShuttingDown) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));
+
+  aWriter.IntProperty("version", 19);
+
+  // The "startTime" field holds the number of milliseconds since midnight
+  // January 1, 1970 GMT. This grotty code computes (Now - (Now -
+  // ProcessStartTime)) to convert CorePS::ProcessStartTime() into that form.
+  TimeDuration delta = TimeStamp::NowUnfuzzed() - CorePS::ProcessStartTime();
+  aWriter.DoubleProperty(
+      "startTime", MicrosecondsSince1970() / 1000.0 - delta.ToMilliseconds());
+
+  // Write the shutdownTime field. Unlike startTime, shutdownTime is not an
+  // absolute time stamp: It's relative to startTime. This is consistent with
+  // all other (non-"startTime") times anywhere in the profile JSON.
+  if (aIsShuttingDown) {
+    aWriter.DoubleProperty("shutdownTime", profiler_time());
+  } else {
+    aWriter.NullProperty("shutdownTime");
+  }
+
+  aWriter.StartArrayProperty("categories");
+  StreamCategories(aWriter);
+  aWriter.EndArray();
+
+  aWriter.StartArrayProperty("markerSchema");
+  StreamMarkerSchema(aWriter);
+  aWriter.EndArray();
+
+  if (!profiler_is_main_thread()) {
+    // Leave the rest of the properties out if we're not on the main thread.
+    // At the moment, the only case in which this function is called on a
+    // background thread is if we're in a content process and are going to
+    // send this profile to the parent process. In that case, the parent
+    // process profile's "meta" object already has the rest of the properties,
+    // and the parent process profile is dumped on that process's main thread.
+    return;
+  }
+
+  aWriter.DoubleProperty("interval", ActivePS::Interval(aLock));
+  aWriter.IntProperty("stackwalk", ActivePS::FeatureStackWalk(aLock));
+
+#ifdef DEBUG
+  aWriter.IntProperty("debug", 1);
+#else
+  aWriter.IntProperty("debug", 0);
+#endif
+
+  aWriter.IntProperty("gcpoison", 0);
+
+  aWriter.IntProperty("asyncstack", 0);
+
+  aWriter.IntProperty("processType", 0);
+}
+
+static void StreamPages(PSLockRef aLock, SpliceableJSONWriter& aWriter) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+  ActivePS::DiscardExpiredPages(aLock);
+  for (const auto& page : ActivePS::ProfiledPages(aLock)) {
+    page->StreamJSON(aWriter);
+  }
+}
+
+static void locked_profiler_stream_json_for_this_process(
+    PSLockRef aLock, SpliceableJSONWriter& aWriter, double aSinceTime,
+    bool aIsShuttingDown, bool aOnlyThreads = false) {
+  LOG("locked_profiler_stream_json_for_this_process");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));
+
+  AUTO_PROFILER_STATS(base_locked_profiler_stream_json_for_this_process);
+
+  const double collectionStartMs = profiler_time();
+
+  ProfileBuffer& buffer = ActivePS::Buffer(aLock);
+
+  // If there is a set "Window length", discard older data.
+  Maybe<double> durationS = ActivePS::Duration(aLock);
+  if (durationS.isSome()) {
+    const double durationStartMs = collectionStartMs - *durationS * 1000;
+    buffer.DiscardSamplesBeforeTime(durationStartMs);
+  }
+
+  if (!aOnlyThreads) {
+    // Put shared library info
+    aWriter.StartArrayProperty("libs");
+    AppendSharedLibraries(aWriter);
+    aWriter.EndArray();
+
+    // Put meta data
+    aWriter.StartObjectProperty("meta");
+    { StreamMetaJSCustomObject(aLock, aWriter, aIsShuttingDown); }
+    aWriter.EndObject();
+
+    // Put page data
+    aWriter.StartArrayProperty("pages");
+    { StreamPages(aLock, aWriter); }
+    aWriter.EndArray();
+
+    buffer.StreamProfilerOverheadToJSON(aWriter, CorePS::ProcessStartTime(),
+                                        aSinceTime);
+    buffer.StreamCountersToJSON(aWriter, CorePS::ProcessStartTime(),
+                                aSinceTime);
+
+    // Lists the samples for each thread profile
+    aWriter.StartArrayProperty("threads");
+  }
+
+  // if aOnlyThreads is true, the only output will be the threads array items.
+  {
+    ActivePS::DiscardExpiredDeadProfiledThreads(aLock);
+    Vector<std::pair<RegisteredThread*, ProfiledThreadData*>> threads =
+        ActivePS::ProfiledThreads(aLock);
+    for (auto& thread : threads) {
+      ProfiledThreadData* profiledThreadData = thread.second;
+      profiledThreadData->StreamJSON(
+          buffer, aWriter, CorePS::ProcessName(aLock), CorePS::ETLDplus1(aLock),
+          CorePS::ProcessStartTime(), aSinceTime);
+    }
+  }
+
+  if (!aOnlyThreads) {
+    aWriter.EndArray();
+
+    aWriter.StartArrayProperty("pausedRanges");
+    { buffer.StreamPausedRangesToJSON(aWriter, aSinceTime); }
+    aWriter.EndArray();
+  }
+
+  const double collectionEndMs = profiler_time();
+
+  // Record timestamps for the collection into the buffer, so that consumers
+  // know why we didn't collect any samples for its duration.
+  // We put these entries into the buffer after we've collected the profile,
+  // so they'll be visible for the *next* profile collection (if they haven't
+  // been overwritten due to buffer wraparound by then).
+  buffer.AddEntry(ProfileBufferEntry::CollectionStart(collectionStartMs));
+  buffer.AddEntry(ProfileBufferEntry::CollectionEnd(collectionEndMs));
+}
+
+bool profiler_stream_json_for_this_process(SpliceableJSONWriter& aWriter,
+                                           double aSinceTime,
+                                           bool aIsShuttingDown,
+                                           bool aOnlyThreads) {
+  LOG("profiler_stream_json_for_this_process");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return false;
+  }
+
+  locked_profiler_stream_json_for_this_process(lock, aWriter, aSinceTime,
+                                               aIsShuttingDown, aOnlyThreads);
+  return true;
+}
+
+// END saving/streaming code
+////////////////////////////////////////////////////////////////////////
+
+static char FeatureCategory(uint32_t aFeature) {
+  if (aFeature & DefaultFeatures()) {
+    if (aFeature & AvailableFeatures()) {
+      return 'D';
+    }
+    return 'd';
+  }
+
+  if (aFeature & StartupExtraDefaultFeatures()) {
+    if (aFeature & AvailableFeatures()) {
+      return 'S';
+    }
+    return 's';
+  }
+
+  if (aFeature & AvailableFeatures()) {
+    return '-';
+  }
+  return 'x';
+}
+
+static void PrintUsageThenExit(int aExitCode) {
+  PrintToConsole(
+      "\n"
+      "Profiler environment variable usage:\n"
+      "\n"
+      "  MOZ_BASE_PROFILER_HELP\n"
+      "  If set to any value, prints this message.\n"
+      "  (Only BaseProfiler features are known here; Use MOZ_PROFILER_HELP\n"
+      "  for Gecko Profiler help, with more features).\n"
+      "\n"
+      "  MOZ_BASE_PROFILER_{,DEBUG_,VERBOSE}LOGGING\n"
+      "  Enables BaseProfiler logging to stdout. The levels of logging\n"
+      "  available are MOZ_BASE_PROFILER_LOGGING' (least verbose),\n"
+      "  '..._DEBUG_LOGGING', '..._VERBOSE_LOGGING' (most verbose)\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP\n"
+      "  If set to any value other than '' or '0'/'N'/'n', starts the\n"
+      "  profiler immediately on start-up.\n"
+      "  Useful if you want profile code that runs very early.\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_ENTRIES=<%u..%u>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the number of entries\n"
+      "  per process in the profiler's circular buffer when the profiler is\n"
+      "  first started.\n"
+      "  If unset, the platform default is used:\n"
+      "  %u entries per process, or %u when MOZ_PROFILER_STARTUP is set.\n"
+      "  (%u bytes per entry -> %u or %u total bytes per process)\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_DURATION=<1..>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the maximum life time\n"
+      "  of entries in the the profiler's circular buffer when the profiler\n"
+      "  is first started, in seconds.\n"
+      "  If unset, the life time of the entries will only be restricted by\n"
+      "  MOZ_PROFILER_STARTUP_ENTRIES (or its default value), and no\n"
+      "  additional time duration restriction will be applied.\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_INTERVAL=<1..1000>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the sample interval,\n"
+      "  measured in milliseconds, when the profiler is first started.\n"
+      "  If unset, the platform default is used.\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_FEATURES_BITFIELD=<Number>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the profiling\n"
+      "  features, as the integer value of the features bitfield.\n"
+      "  If unset, the value from MOZ_PROFILER_STARTUP_FEATURES is used.\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_FEATURES=<Features>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the profiling\n"
+      "  features, as a comma-separated list of strings.\n"
+      "  Ignored if MOZ_PROFILER_STARTUP_FEATURES_BITFIELD is set.\n"
+      "  If unset, the platform default is used.\n"
+      "\n"
+      "    Features: (x=unavailable, D/d=default/unavailable,\n"
+      "               S/s=MOZ_PROFILER_STARTUP extra "
+      "default/unavailable)\n",
+      unsigned(ActivePS::scMinimumBufferEntries),
+      unsigned(ActivePS::scMaximumBufferEntries),
+      unsigned(BASE_PROFILER_DEFAULT_ENTRIES.Value()),
+      unsigned(BASE_PROFILER_DEFAULT_STARTUP_ENTRIES.Value()),
+      unsigned(scBytesPerEntry),
+      unsigned(BASE_PROFILER_DEFAULT_ENTRIES.Value() * scBytesPerEntry),
+      unsigned(BASE_PROFILER_DEFAULT_STARTUP_ENTRIES.Value() *
+               scBytesPerEntry));
+
+#define PRINT_FEATURE(n_, str_, Name_, desc_)             \
+  PrintToConsole("    %c %7u: \"%s\" (%s)\n",             \
+                 FeatureCategory(ProfilerFeature::Name_), \
+                 ProfilerFeature::Name_, str_, desc_);
+
+  BASE_PROFILER_FOR_EACH_FEATURE(PRINT_FEATURE)
+
+#undef PRINT_FEATURE
+
+  PrintToConsole(
+      "    -        \"default\" (All above D+S defaults)\n"
+      "\n"
+      "  MOZ_PROFILER_STARTUP_FILTERS=<Filters>\n"
+      "  If MOZ_PROFILER_STARTUP is set, specifies the thread filters, as "
+      "a\n"
+      "  comma-separated list of strings. A given thread will be sampled if\n"
+      "  any of the filters is a case-insensitive substring of the thread\n"
+      "  name. If unset, a default is used.\n"
+      "\n"
+      "  MOZ_PROFILER_SHUTDOWN\n"
+      "  If set, the profiler saves a profile to the named file on shutdown.\n"
+      "\n"
+      "  MOZ_PROFILER_SYMBOLICATE\n"
+      "  If set, the profiler will pre-symbolicate profiles.\n"
+      "  *Note* This will add a significant pause when gathering data, and\n"
+      "  is intended mainly for local development.\n"
+      "\n"
+      "  MOZ_PROFILER_LUL_TEST\n"
+      "  If set to any value, runs LUL unit tests at startup.\n"
+      "\n"
+      "  This platform %s native unwinding.\n"
+      "\n",
+#if defined(HAVE_NATIVE_UNWIND)
+      "supports"
+#else
+      "does not support"
+#endif
+  );
+
+  exit(aExitCode);
+}
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN Sampler
+
+#if defined(GP_OS_linux) || defined(GP_OS_android)
+struct SigHandlerCoordinator;
+#endif
+
+// Sampler performs setup and teardown of the state required to sample with the
+// profiler. Sampler may exist when ActivePS is not present.
+//
+// SuspendAndSampleAndResumeThread must only be called from a single thread,
+// and must not sample the thread it is being called from. A separate Sampler
+// instance must be used for each thread which wants to capture samples.
+
+// WARNING WARNING WARNING WARNING WARNING WARNING WARNING WARNING
+//
+// With the exception of SamplerThread, all Sampler objects must be Disable-d
+// before releasing the lock which was used to create them. This avoids races
+// on linux with the SIGPROF signal handler.
+
+class Sampler {
+ public:
+  // Sets up the profiler such that it can begin sampling.
+  explicit Sampler(PSLockRef aLock);
+
+  // Disable the sampler, restoring it to its previous state. This must be
+  // called once, and only once, before the Sampler is destroyed.
+  void Disable(PSLockRef aLock);
+
+  // This method suspends and resumes the samplee thread. It calls the passed-in
+  // function-like object aProcessRegs (passing it a populated |const
+  // Registers&| arg) while the samplee thread is suspended.
+  //
+  // Func must be a function-like object of type `void()`.
+  template <typename Func>
+  void SuspendAndSampleAndResumeThread(
+      PSLockRef aLock, const RegisteredThread& aRegisteredThread,
+      const TimeStamp& aNow, const Func& aProcessRegs);
+
+ private:
+#if defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
+  // Used to restore the SIGPROF handler when ours is removed.
+  struct sigaction mOldSigprofHandler;
+
+  // This process' ID. Needed as an argument for tgkill in
+  // SuspendAndSampleAndResumeThread.
+  int mMyPid;
+
+  // The sampler thread's ID.  Used to assert that it is not sampling itself,
+  // which would lead to deadlock.
+  int mSamplerTid;
+
+ public:
+  // This is the one-and-only variable used to communicate between the sampler
+  // thread and the samplee thread's signal handler. It's static because the
+  // samplee thread's signal handler is static.
+  static struct SigHandlerCoordinator* sSigHandlerCoordinator;
+#endif
+};
+
+// END Sampler
+////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN SamplerThread
+
+// The sampler thread controls sampling and runs whenever the profiler is
+// active. It periodically runs through all registered threads, finds those
+// that should be sampled, then pauses and samples them.
+
+class SamplerThread {
+ public:
+  // Creates a sampler thread, but doesn't start it.
+  SamplerThread(PSLockRef aLock, uint32_t aActivityGeneration,
+                double aIntervalMilliseconds);
+  ~SamplerThread();
+
+  // This runs on (is!) the sampler thread.
+  void Run();
+
+  // This runs on the main thread.
+  void Stop(PSLockRef aLock);
+
+ private:
+  // This suspends the calling thread for the given number of microseconds.
+  // Best effort timing.
+  void SleepMicro(uint32_t aMicroseconds);
+
+  // The sampler used to suspend and sample threads.
+  Sampler mSampler;
+
+  // The activity generation, for detecting when the sampler thread must stop.
+  const uint32_t mActivityGeneration;
+
+  // The interval between samples, measured in microseconds.
+  const int mIntervalMicroseconds;
+
+  // The OS-specific handle for the sampler thread.
+#if defined(GP_OS_windows)
+  HANDLE mThread;
+#elif defined(GP_OS_darwin) || defined(GP_OS_linux) || \
+    defined(GP_OS_android) || defined(GP_OS_freebsd)
+  pthread_t mThread;
+#endif
+
+  SamplerThread(const SamplerThread&) = delete;
+  void operator=(const SamplerThread&) = delete;
+};
+
+// This function is required because we need to create a SamplerThread within
+// ActivePS's constructor, but SamplerThread is defined after ActivePS. It
+// could probably be removed by moving some code around.
+static SamplerThread* NewSamplerThread(PSLockRef aLock, uint32_t aGeneration,
+                                       double aInterval) {
+  return new SamplerThread(aLock, aGeneration, aInterval);
+}
+
+// This function is the sampler thread.  This implementation is used for all
+// targets.
+void SamplerThread::Run() {
+  // TODO: If possible, name this thread later on, after NSPR becomes available.
+  // PR_SetCurrentThreadName("SamplerThread");
+
+  // Features won't change during this SamplerThread's lifetime, so we can read
+  // them once and store them locally.
+  const uint32_t features = []() -> uint32_t {
+    PSAutoLock lock;
+    if (!ActivePS::Exists(lock)) {
+      // If there is no active profiler, it doesn't matter what we return,
+      // because this thread will exit before any feature is used.
+      return 0;
+    }
+    return ActivePS::Features(lock);
+  }();
+
+  // Not *no*-stack-sampling means we do want stack sampling.
+  const bool stackSampling = !ProfilerFeature::HasNoStackSampling(features);
+
+  // Use local BlocksRingBuffer&ProfileBuffer to capture the stack.
+  // (This is to avoid touching the CorePS::CoreBuffer lock while
+  // a thread is suspended, because that thread could be working with
+  // the CorePS::CoreBuffer as well.)
+  ProfileBufferChunkManagerSingle localChunkManager(
+      ProfileBufferChunkManager::scExpectedMaximumStackSize);
+  ProfileChunkedBuffer localBuffer(
+      ProfileChunkedBuffer::ThreadSafety::WithoutMutex, localChunkManager);
+  ProfileBuffer localProfileBuffer(localBuffer);
+
+  // Will be kept between collections, to know what each collection does.
+  auto previousState = localBuffer.GetState();
+
+  // This will be positive if we are running behind schedule (sampling less
+  // frequently than desired) and negative if we are ahead of schedule.
+  TimeDuration lastSleepOvershoot = 0;
+  TimeStamp sampleStart = TimeStamp::NowUnfuzzed();
+
+  while (true) {
+    // This scope is for |lock|. It ends before we sleep below.
+    {
+      PSAutoLock lock;
+      TimeStamp lockAcquired = TimeStamp::NowUnfuzzed();
+
+      if (!ActivePS::Exists(lock)) {
+        return;
+      }
+
+      // At this point profiler_stop() might have been called, and
+      // profiler_start() might have been called on another thread. If this
+      // happens the generation won't match.
+      if (ActivePS::Generation(lock) != mActivityGeneration) {
+        return;
+      }
+
+      ActivePS::ClearExpiredExitProfiles(lock);
+
+      TimeStamp expiredMarkersCleaned = TimeStamp::NowUnfuzzed();
+
+      if (!ActivePS::IsSamplingPaused(lock)) {
+        TimeDuration delta = sampleStart - CorePS::ProcessStartTime();
+        ProfileBuffer& buffer = ActivePS::Buffer(lock);
+
+        // handle per-process generic counters
+        const Vector<BaseProfilerCount*>& counters = CorePS::Counters(lock);
+        for (auto& counter : counters) {
+          // create Buffer entries for each counter
+          buffer.AddEntry(ProfileBufferEntry::CounterId(counter));
+          buffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));
+          // XXX support keyed maps of counts
+          // In the future, we'll support keyed counters - for example, counters
+          // with a key which is a thread ID. For "simple" counters we'll just
+          // use a key of 0.
+          int64_t count;
+          uint64_t number;
+          counter->Sample(count, number);
+          buffer.AddEntry(ProfileBufferEntry::CounterKey(0));
+          buffer.AddEntry(ProfileBufferEntry::Count(count));
+          if (number) {
+            buffer.AddEntry(ProfileBufferEntry::Number(number));
+          }
+        }
+        TimeStamp countersSampled = TimeStamp::NowUnfuzzed();
+
+        if (stackSampling) {
+          const Vector<LiveProfiledThreadData>& liveThreads =
+              ActivePS::LiveProfiledThreads(lock);
+
+          for (auto& thread : liveThreads) {
+            RegisteredThread* registeredThread = thread.mRegisteredThread;
+            ProfiledThreadData* profiledThreadData =
+                thread.mProfiledThreadData.get();
+            RefPtr<ThreadInfo> info = registeredThread->Info();
+
+            // If the thread is asleep and has been sampled before in the same
+            // sleep episode, find and copy the previous sample, as that's
+            // cheaper than taking a new sample.
+            if (registeredThread->RacyRegisteredThread()
+                    .CanDuplicateLastSampleDueToSleep()) {
+              bool dup_ok = ActivePS::Buffer(lock).DuplicateLastSample(
+                  info->ThreadId(), CorePS::ProcessStartTime(),
+                  profiledThreadData->LastSample());
+              if (dup_ok) {
+                continue;
+              }
+            }
+
+            AUTO_PROFILER_STATS(base_SamplerThread_Run_DoPeriodicSample);
+
+            TimeStamp now = TimeStamp::NowUnfuzzed();
+
+            // Add the thread ID now, so we know its position in the main
+            // buffer, which is used by some JS data. (DoPeriodicSample only
+            // knows about the temporary local buffer.)
+            uint64_t samplePos =
+                buffer.AddThreadIdEntry(registeredThread->Info()->ThreadId());
+            profiledThreadData->LastSample() = Some(samplePos);
+
+            // Also add the time, so it's always there after the thread ID, as
+            // expected by the parser. (Other stack data is optional.)
+            TimeDuration delta = now - CorePS::ProcessStartTime();
+            buffer.AddEntry(ProfileBufferEntry::Time(delta.ToMilliseconds()));
+
+            mSampler.SuspendAndSampleAndResumeThread(
+                lock, *registeredThread, now,
+                [&](const Registers& aRegs, const TimeStamp& aNow) {
+                  DoPeriodicSample(lock, *registeredThread, *profiledThreadData,
+                                   aRegs, samplePos, localProfileBuffer);
+                });
+
+            // If data is complete, copy it into the global buffer.
+            auto state = localBuffer.GetState();
+            if (state.mClearedBlockCount != previousState.mClearedBlockCount) {
+              LOG("Stack sample too big for local storage, needed %u bytes",
+                  unsigned(state.mRangeEnd - previousState.mRangeEnd));
+            } else if (state.mRangeEnd - previousState.mRangeEnd >=
+                       *CorePS::CoreBuffer().BufferLength()) {
+              LOG("Stack sample too big for profiler storage, needed %u bytes",
+                  unsigned(state.mRangeEnd - previousState.mRangeEnd));
+            } else {
+              CorePS::CoreBuffer().AppendContents(localBuffer);
+            }
+
+            // Clean up for the next run.
+            localBuffer.Clear();
+            previousState = localBuffer.GetState();
+          }
+        }
+
+#if defined(USE_LUL_STACKWALK)
+        // The LUL unwind object accumulates frame statistics. Periodically we
+        // should poke it to give it a chance to print those statistics.  This
+        // involves doing I/O (fprintf, __android_log_print, etc.) and so
+        // can't safely be done from the critical section inside
+        // SuspendAndSampleAndResumeThread, which is why it is done here.
+        CorePS::Lul(lock)->MaybeShowStats();
+#endif
+        TimeStamp threadsSampled = TimeStamp::NowUnfuzzed();
+
+        {
+          AUTO_PROFILER_STATS(Sampler_FulfillChunkRequests);
+          ActivePS::FulfillChunkRequests(lock);
+        }
+
+        buffer.CollectOverheadStats(delta, lockAcquired - sampleStart,
+                                    expiredMarkersCleaned - lockAcquired,
+                                    countersSampled - expiredMarkersCleaned,
+                                    threadsSampled - countersSampled);
+      }
+    }
+    // gPSMutex is not held after this point.
+
+    // Calculate how long a sleep to request.  After the sleep, measure how
+    // long we actually slept and take the difference into account when
+    // calculating the sleep interval for the next iteration.  This is an
+    // attempt to keep "to schedule" in the presence of inaccuracy of the
+    // actual sleep intervals.
+    TimeStamp targetSleepEndTime =
+        sampleStart + TimeDuration::FromMicroseconds(mIntervalMicroseconds);
+    TimeStamp beforeSleep = TimeStamp::NowUnfuzzed();
+    TimeDuration targetSleepDuration = targetSleepEndTime - beforeSleep;
+    double sleepTime = std::max(
+        0.0, (targetSleepDuration - lastSleepOvershoot).ToMicroseconds());
+    SleepMicro(static_cast<uint32_t>(sleepTime));
+    sampleStart = TimeStamp::NowUnfuzzed();
+    lastSleepOvershoot =
+        sampleStart - (beforeSleep + TimeDuration::FromMicroseconds(sleepTime));
+  }
+}
+
+// Temporary closing namespaces from enclosing platform.cpp.
+}  // namespace baseprofiler
+}  // namespace mozilla
+
+// We #include these files directly because it means those files can use
+// declarations from this file trivially.  These provide target-specific
+// implementations of all SamplerThread methods except Run().
+#if defined(GP_OS_windows)
+#  include "platform-win32.cpp"
+#elif defined(GP_OS_darwin)
+#  include "platform-macos.cpp"
+#elif defined(GP_OS_linux) || defined(GP_OS_android) || defined(GP_OS_freebsd)
+#  include "platform-linux-android.cpp"
+#else
+#  error "bad platform"
+#endif
+
+namespace mozilla {
+namespace baseprofiler {
+
+UniquePlatformData AllocPlatformData(int aThreadId) {
+  return UniquePlatformData(new PlatformData(aThreadId));
+}
+
+void PlatformDataDestructor::operator()(PlatformData* aData) { delete aData; }
+
+// END SamplerThread
+////////////////////////////////////////////////////////////////////////
+
+////////////////////////////////////////////////////////////////////////
+// BEGIN externally visible functions
+
+static uint32_t ParseFeature(const char* aFeature, bool aIsStartup) {
+  if (strcmp(aFeature, "default") == 0) {
+    return (aIsStartup ? (DefaultFeatures() | StartupExtraDefaultFeatures())
+                       : DefaultFeatures()) &
+           AvailableFeatures();
+  }
+
+#define PARSE_FEATURE_BIT(n_, str_, Name_, desc_) \
+  if (strcmp(aFeature, str_) == 0) {              \
+    return ProfilerFeature::Name_;                \
+  }
+
+  BASE_PROFILER_FOR_EACH_FEATURE(PARSE_FEATURE_BIT)
+
+#undef PARSE_FEATURE_BIT
+
+  PrintToConsole("\nUnrecognized feature \"%s\".\n\n", aFeature);
+  // Since we may have an old feature we don't implement anymore, don't exit
+  PrintUsageThenExit(0);
+  return 0;
+}
+
+uint32_t ParseFeaturesFromStringArray(const char** aFeatures,
+                                      uint32_t aFeatureCount,
+                                      bool aIsStartup /* = false */) {
+  uint32_t features = 0;
+  for (size_t i = 0; i < aFeatureCount; i++) {
+    features |= ParseFeature(aFeatures[i], aIsStartup);
+  }
+  return features;
+}
+
+// Find the RegisteredThread for the current thread. This should only be called
+// in places where TLSRegisteredThread can't be used.
+static RegisteredThread* FindCurrentThreadRegisteredThread(PSLockRef aLock) {
+  int id = profiler_current_thread_id();
+  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
+      CorePS::RegisteredThreads(aLock);
+  for (auto& registeredThread : registeredThreads) {
+    if (registeredThread->Info()->ThreadId() == id) {
+      return registeredThread.get();
+    }
+  }
+
+  return nullptr;
+}
+
+static ProfilingStack* locked_register_thread(PSLockRef aLock,
+                                              const char* aName,
+                                              void* aStackTop) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  MOZ_ASSERT(!FindCurrentThreadRegisteredThread(aLock));
+
+  VTUNE_REGISTER_THREAD(aName);
+
+  if (!TLSRegisteredThread::Init(aLock)) {
+    return nullptr;
+  }
+
+  RefPtr<ThreadInfo> info = new ThreadInfo(aName, profiler_current_thread_id(),
+                                           profiler_is_main_thread());
+  UniquePtr<RegisteredThread> registeredThread =
+      MakeUnique<RegisteredThread>(info, aStackTop);
+
+  TLSRegisteredThread::SetRegisteredThread(aLock, registeredThread.get());
+
+  if (ActivePS::Exists(aLock) && ActivePS::ShouldProfileThread(aLock, info)) {
+    registeredThread->RacyRegisteredThread().SetIsBeingProfiled(true);
+    ActivePS::AddLiveProfiledThread(aLock, registeredThread.get(),
+                                    MakeUnique<ProfiledThreadData>(info));
+  }
+
+  ProfilingStack* profilingStack =
+      &registeredThread->RacyRegisteredThread().ProfilingStack();
+
+  CorePS::AppendRegisteredThread(aLock, std::move(registeredThread));
+
+  return profilingStack;
+}
+
+static void locked_profiler_start(PSLockRef aLock, PowerOfTwo32 aCapacity,
+                                  double aInterval, uint32_t aFeatures,
+                                  const char** aFilters, uint32_t aFilterCount,
+                                  const Maybe<double>& aDuration);
+
+static Vector<const char*> SplitAtCommas(const char* aString,
+                                         UniquePtr<char[]>& aStorage) {
+  size_t len = strlen(aString);
+  aStorage = MakeUnique<char[]>(len + 1);
+  PodCopy(aStorage.get(), aString, len + 1);
+
+  // Iterate over all characters in aStorage and split at commas, by
+  // overwriting commas with the null char.
+  Vector<const char*> array;
+  size_t currentElementStart = 0;
+  for (size_t i = 0; i <= len; i++) {
+    if (aStorage[i] == ',') {
+      aStorage[i] = '\0';
+    }
+    if (aStorage[i] == '\0') {
+      MOZ_RELEASE_ASSERT(array.append(&aStorage[currentElementStart]));
+      currentElementStart = i + 1;
+    }
+  }
+  return array;
+}
+
+void profiler_init(void* aStackTop) {
+  LOG("profiler_init");
+
+  scProfilerMainThreadId = profiler_current_thread_id();
+
+  VTUNE_INIT();
+
+  MOZ_RELEASE_ASSERT(!CorePS::Exists());
+
+  if (getenv("MOZ_BASE_PROFILER_HELP")) {
+    PrintUsageThenExit(0);  // terminates execution
+  }
+
+  SharedLibraryInfo::Initialize();
+
+  uint32_t features = DefaultFeatures() & AvailableFeatures();
+
+  UniquePtr<char[]> filterStorage;
+
+  Vector<const char*> filters;
+  MOZ_RELEASE_ASSERT(filters.append(kMainThreadName));
+
+  PowerOfTwo32 capacity = BASE_PROFILER_DEFAULT_ENTRIES;
+  Maybe<double> duration = Nothing();
+  double interval = BASE_PROFILER_DEFAULT_INTERVAL;
+
+  {
+    PSAutoLock lock;
+
+    // We've passed the possible failure point. Instantiate CorePS, which
+    // indicates that the profiler has initialized successfully.
+    CorePS::Create(lock);
+
+    Unused << locked_register_thread(lock, kMainThreadName, aStackTop);
+
+    // Platform-specific initialization.
+    PlatformInit(lock);
+
+    // (Linux-only) We could create CorePS::mLul and read unwind info into it
+    // at this point. That would match the lifetime implied by destruction of
+    // it in profiler_shutdown() just below. However, that gives a big delay on
+    // startup, even if no profiling is actually to be done. So, instead, it is
+    // created on demand at the first call to PlatformStart().
+
+    const char* startupEnv = getenv("MOZ_PROFILER_STARTUP");
+    if (!startupEnv || startupEnv[0] == '\0' ||
+        ((startupEnv[0] == '0' || startupEnv[0] == 'N' ||
+          startupEnv[0] == 'n') &&
+         startupEnv[1] == '\0')) {
+      return;
+    }
+
+    // Hidden option to stop Base Profiler, mostly due to Talos intermittents,
+    // see https://bugzilla.mozilla.org/show_bug.cgi?id=1638851#c3
+    // TODO: Investigate root cause and remove this in bugs 1648324 and 1648325.
+    if (getenv("MOZ_PROFILER_STARTUP_NO_BASE")) {
+      return;
+    }
+
+    LOG("- MOZ_PROFILER_STARTUP is set");
+
+    // Startup default capacity may be different.
+    capacity = BASE_PROFILER_DEFAULT_STARTUP_ENTRIES;
+
+    const char* startupCapacity = getenv("MOZ_PROFILER_STARTUP_ENTRIES");
+    if (startupCapacity && startupCapacity[0] != '\0') {
+      errno = 0;
+      long capacityLong = strtol(startupCapacity, nullptr, 10);
+      // `long` could be 32 or 64 bits, so we force a 64-bit comparison with
+      // the maximum 32-bit signed number (as more than that is clamped down to
+      // 2^31 anyway).
+      if (errno == 0 && capacityLong > 0 &&
+          static_cast<uint64_t>(capacityLong) <=
+              static_cast<uint64_t>(INT32_MAX)) {
+        capacity = PowerOfTwo32(ActivePS::ClampToAllowedEntries(
+            static_cast<uint32_t>(capacityLong)));
+        LOG("- MOZ_PROFILER_STARTUP_ENTRIES = %u", unsigned(capacity.Value()));
+      } else {
+        PrintToConsole("- MOZ_PROFILER_STARTUP_ENTRIES not a valid integer: %s",
+                       startupCapacity);
+        PrintUsageThenExit(1);
+      }
+    }
+
+    const char* startupDuration = getenv("MOZ_PROFILER_STARTUP_DURATION");
+    if (startupDuration && startupDuration[0] != '\0') {
+      // The duration is a floating point number. Use StringToDouble rather than
+      // strtod, so that "." is used as the decimal separator regardless of OS
+      // locale.
+      auto durationVal = StringToDouble(std::string(startupDuration));
+      if (durationVal && *durationVal >= 0.0) {
+        if (*durationVal > 0.0) {
+          duration = Some(*durationVal);
+        }
+        LOG("- MOZ_PROFILER_STARTUP_DURATION = %f", *durationVal);
+      } else {
+        PrintToConsole("- MOZ_PROFILER_STARTUP_DURATION not a valid float: %s",
+                       startupDuration);
+        PrintUsageThenExit(1);
+      }
+    }
+
+    const char* startupInterval = getenv("MOZ_PROFILER_STARTUP_INTERVAL");
+    if (startupInterval && startupInterval[0] != '\0') {
+      // The interval is a floating point number. Use StringToDouble rather than
+      // strtod, so that "." is used as the decimal separator regardless of OS
+      // locale.
+      auto intervalValue = StringToDouble(MakeStringSpan(startupInterval));
+      if (intervalValue && *intervalValue > 0.0 && *intervalValue <= 1000.0) {
+        interval = *intervalValue;
+        LOG("- MOZ_PROFILER_STARTUP_INTERVAL = %f", interval);
+      } else {
+        PrintToConsole("- MOZ_PROFILER_STARTUP_INTERVAL not a valid float: %s",
+                       startupInterval);
+        PrintUsageThenExit(1);
+      }
+    }
+
+    features |= StartupExtraDefaultFeatures() & AvailableFeatures();
+
+    const char* startupFeaturesBitfield =
+        getenv("MOZ_PROFILER_STARTUP_FEATURES_BITFIELD");
+    if (startupFeaturesBitfield && startupFeaturesBitfield[0] != '\0') {
+      errno = 0;
+      features = strtol(startupFeaturesBitfield, nullptr, 10);
+      if (errno == 0 && features != 0) {
+        LOG("- MOZ_PROFILER_STARTUP_FEATURES_BITFIELD = %d", features);
+      } else {
+        PrintToConsole(
+            "- MOZ_PROFILER_STARTUP_FEATURES_BITFIELD not a valid integer: %s",
+            startupFeaturesBitfield);
+        PrintUsageThenExit(1);
+      }
+    } else {
+      const char* startupFeatures = getenv("MOZ_PROFILER_STARTUP_FEATURES");
+      if (startupFeatures && startupFeatures[0] != '\0') {
+        // Interpret startupFeatures as a list of feature strings, separated by
+        // commas.
+        UniquePtr<char[]> featureStringStorage;
+        Vector<const char*> featureStringArray =
+            SplitAtCommas(startupFeatures, featureStringStorage);
+        features = ParseFeaturesFromStringArray(featureStringArray.begin(),
+                                                featureStringArray.length(),
+                                                /* aIsStartup */ true);
+        LOG("- MOZ_PROFILER_STARTUP_FEATURES = %d", features);
+      }
+    }
+
+    const char* startupFilters = getenv("MOZ_PROFILER_STARTUP_FILTERS");
+    if (startupFilters && startupFilters[0] != '\0') {
+      filters = SplitAtCommas(startupFilters, filterStorage);
+      LOG("- MOZ_PROFILER_STARTUP_FILTERS = %s", startupFilters);
+    }
+
+    locked_profiler_start(lock, capacity, interval, features, filters.begin(),
+                          filters.length(), duration);
+  }
+
+  // TODO: Install memory counter if it is possible from mozglue.
+  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
+  //   // start counting memory allocations (outside of lock because this may
+  //   call
+  //   // profiler_add_sampled_counter which would attempt to take the lock.)
+  //   mozilla::profiler::install_memory_counter(true);
+  // #endif
+}
+
+static void locked_profiler_save_profile_to_file(PSLockRef aLock,
+                                                 const char* aFilename,
+                                                 bool aIsShuttingDown);
+
+static SamplerThread* locked_profiler_stop(PSLockRef aLock);
+
+void profiler_shutdown() {
+  LOG("profiler_shutdown");
+
+  VTUNE_SHUTDOWN();
+
+  MOZ_RELEASE_ASSERT(profiler_is_main_thread());
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  // If the profiler is active we must get a handle to the SamplerThread before
+  // ActivePS is destroyed, in order to delete it.
+  SamplerThread* samplerThread = nullptr;
+  {
+    PSAutoLock lock;
+
+    // Save the profile on shutdown if requested.
+    if (ActivePS::Exists(lock)) {
+      const char* filename = getenv("MOZ_PROFILER_SHUTDOWN");
+      if (filename) {
+        locked_profiler_save_profile_to_file(lock, filename,
+                                             /* aIsShuttingDown */ true);
+      }
+
+      samplerThread = locked_profiler_stop(lock);
+    }
+
+    CorePS::Destroy(lock);
+
+    // We just destroyed CorePS and the ThreadInfos it contains, so we can
+    // clear this thread's TLSRegisteredThread.
+    TLSRegisteredThread::SetRegisteredThread(lock, nullptr);
+  }
+
+  // We do these operations with gPSMutex unlocked. The comments in
+  // profiler_stop() explain why.
+  if (samplerThread) {
+    delete samplerThread;
+  }
+}
+
+static bool WriteProfileToJSONWriter(SpliceableChunkedJSONWriter& aWriter,
+                                     double aSinceTime, bool aIsShuttingDown,
+                                     bool aOnlyThreads = false) {
+  LOG("WriteProfileToJSONWriter");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  if (!aOnlyThreads) {
+    aWriter.Start();
+    {
+      if (!profiler_stream_json_for_this_process(
+              aWriter, aSinceTime, aIsShuttingDown, aOnlyThreads)) {
+        return false;
+      }
+
+      // Don't include profiles from other processes because this is a
+      // synchronous function.
+      aWriter.StartArrayProperty("processes");
+      aWriter.EndArray();
+    }
+    aWriter.End();
+  } else {
+    aWriter.StartBareList();
+    if (!profiler_stream_json_for_this_process(aWriter, aSinceTime,
+                                               aIsShuttingDown, aOnlyThreads)) {
+      return false;
+    }
+    aWriter.EndBareList();
+  }
+  return true;
+}
+
+void profiler_set_process_name(const std::string& aProcessName,
+                               const std::string* aETLDplus1) {
+  LOG("profiler_set_process_name(\"%s\", \"%s\")", aProcessName.c_str(),
+      aETLDplus1 ? aETLDplus1->c_str() : "<none>");
+  PSAutoLock lock;
+  CorePS::SetProcessName(lock, aProcessName);
+  if (aETLDplus1) {
+    CorePS::SetETLDplus1(lock, *aETLDplus1);
+  }
+}
+
+UniquePtr<char[]> profiler_get_profile(double aSinceTime, bool aIsShuttingDown,
+                                       bool aOnlyThreads) {
+  LOG("profiler_get_profile");
+
+  SpliceableChunkedJSONWriter b;
+  if (!WriteProfileToJSONWriter(b, aSinceTime, aIsShuttingDown, aOnlyThreads)) {
+    return nullptr;
+  }
+  return b.ChunkedWriteFunc().CopyData();
+}
+
+void profiler_get_profile_json_into_lazily_allocated_buffer(
+    const std::function<char*(size_t)>& aAllocator, double aSinceTime,
+    bool aIsShuttingDown) {
+  LOG("profiler_get_profile_json_into_lazily_allocated_buffer");
+
+  SpliceableChunkedJSONWriter b;
+  if (!WriteProfileToJSONWriter(b, aSinceTime, aIsShuttingDown)) {
+    return;
+  }
+
+  b.ChunkedWriteFunc().CopyDataIntoLazilyAllocatedBuffer(aAllocator);
+}
+
+void profiler_get_start_params(int* aCapacity, Maybe<double>* aDuration,
+                               double* aInterval, uint32_t* aFeatures,
+                               Vector<const char*>* aFilters) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  if (!aCapacity || !aDuration || !aInterval || !aFeatures || !aFilters) {
+    return;
+  }
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    *aCapacity = 0;
+    *aDuration = Nothing();
+    *aInterval = 0;
+    *aFeatures = 0;
+    aFilters->clear();
+    return;
+  }
+
+  *aCapacity = ActivePS::Capacity(lock).Value();
+  *aDuration = ActivePS::Duration(lock);
+  *aInterval = ActivePS::Interval(lock);
+  *aFeatures = ActivePS::Features(lock);
+
+  const Vector<std::string>& filters = ActivePS::Filters(lock);
+  MOZ_ALWAYS_TRUE(aFilters->resize(filters.length()));
+  for (uint32_t i = 0; i < filters.length(); ++i) {
+    (*aFilters)[i] = filters[i].c_str();
+  }
+}
+
+void GetProfilerEnvVarsForChildProcess(
+    std::function<void(const char* key, const char* value)>&& aSetEnv) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    aSetEnv("MOZ_PROFILER_STARTUP", "");
+    return;
+  }
+
+  aSetEnv("MOZ_PROFILER_STARTUP", "1");
+  auto capacityString =
+      Smprintf("%u", unsigned(ActivePS::Capacity(lock).Value()));
+  aSetEnv("MOZ_PROFILER_STARTUP_ENTRIES", capacityString.get());
+
+  // Use AppendFloat instead of Smprintf with %f because the decimal
+  // separator used by %f is locale-dependent. But the string we produce needs
+  // to be parseable by strtod, which only accepts the period character as a
+  // decimal separator. AppendFloat always uses the period character.
+  std::string intervalString = std::to_string(ActivePS::Interval(lock));
+  aSetEnv("MOZ_PROFILER_STARTUP_INTERVAL", intervalString.c_str());
+
+  auto featuresString = Smprintf("%d", ActivePS::Features(lock));
+  aSetEnv("MOZ_PROFILER_STARTUP_FEATURES_BITFIELD", featuresString.get());
+
+  std::string filtersString;
+  const Vector<std::string>& filters = ActivePS::Filters(lock);
+  for (uint32_t i = 0; i < filters.length(); ++i) {
+    filtersString += filters[i];
+    if (i != filters.length() - 1) {
+      filtersString += ",";
+    }
+  }
+  aSetEnv("MOZ_PROFILER_STARTUP_FILTERS", filtersString.c_str());
+}
+
+void profiler_received_exit_profile(const std::string& aExitProfile) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+  PSAutoLock lock;
+  if (!ActivePS::Exists(lock)) {
+    return;
+  }
+  ActivePS::AddExitProfile(lock, aExitProfile);
+}
+
+Vector<std::string> profiler_move_exit_profiles() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+  PSAutoLock lock;
+  Vector<std::string> profiles;
+  if (ActivePS::Exists(lock)) {
+    profiles = ActivePS::MoveExitProfiles(lock);
+  }
+  return profiles;
+}
+
+static void locked_profiler_save_profile_to_file(PSLockRef aLock,
+                                                 const char* aFilename,
+                                                 bool aIsShuttingDown = false) {
+  LOG("locked_profiler_save_profile_to_file(%s)", aFilename);
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));
+
+  std::ofstream stream;
+  stream.open(aFilename);
+  if (stream.is_open()) {
+    SpliceableJSONWriter w(MakeUnique<OStreamJSONWriteFunc>(stream));
+    w.Start();
+    {
+      locked_profiler_stream_json_for_this_process(aLock, w, /* sinceTime */ 0,
+                                                   aIsShuttingDown);
+
+      w.StartArrayProperty("processes");
+      Vector<std::string> exitProfiles = ActivePS::MoveExitProfiles(aLock);
+      for (auto& exitProfile : exitProfiles) {
+        if (!exitProfile.empty()) {
+          w.Splice(exitProfile);
+        }
+      }
+      w.EndArray();
+    }
+    w.End();
+
+    stream.close();
+  }
+}
+
+void profiler_save_profile_to_file(const char* aFilename) {
+  LOG("profiler_save_profile_to_file(%s)", aFilename);
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return;
+  }
+
+  locked_profiler_save_profile_to_file(lock, aFilename);
+}
+
+uint32_t profiler_get_available_features() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+  return AvailableFeatures();
+}
+
+Maybe<ProfilerBufferInfo> profiler_get_buffer_info() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return Nothing();
+  }
+
+  return Some(ActivePS::Buffer(lock).GetProfilerBufferInfo());
+}
+
+// This basically duplicates AutoProfilerLabel's constructor.
+static void* MozGlueBaseLabelEnter(const char* aLabel,
+                                   const char* aDynamicString, void* aSp) {
+  ProfilingStack* profilingStack = AutoProfilerLabel::sProfilingStack.get();
+  if (profilingStack) {
+    profilingStack->pushLabelFrame(aLabel, aDynamicString, aSp,
+                                   ProfilingCategoryPair::OTHER);
+  }
+  return profilingStack;
+}
+
+// This basically duplicates AutoProfilerLabel's destructor.
+static void MozGlueBaseLabelExit(void* sProfilingStack) {
+  if (sProfilingStack) {
+    reinterpret_cast<ProfilingStack*>(sProfilingStack)->pop();
+  }
+}
+
+static void locked_profiler_start(PSLockRef aLock, PowerOfTwo32 aCapacity,
+                                  double aInterval, uint32_t aFeatures,
+                                  const char** aFilters, uint32_t aFilterCount,
+                                  const Maybe<double>& aDuration) {
+  if (LOG_TEST) {
+    LOG("locked_profiler_start");
+    LOG("- capacity  = %d", int(aCapacity.Value()));
+    LOG("- duration  = %.2f", aDuration ? *aDuration : -1);
+    LOG("- interval = %.2f", aInterval);
+
+#define LOG_FEATURE(n_, str_, Name_, desc_)     \
+  if (ProfilerFeature::Has##Name_(aFeatures)) { \
+    LOG("- feature  = %s", str_);               \
+  }
+
+    BASE_PROFILER_FOR_EACH_FEATURE(LOG_FEATURE)
+
+#undef LOG_FEATURE
+
+    for (uint32_t i = 0; i < aFilterCount; i++) {
+      LOG("- threads  = %s", aFilters[i]);
+    }
+  }
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists() && !ActivePS::Exists(aLock));
+
+#if defined(GP_PLAT_amd64_windows)
+  InitializeWin64ProfilerHooks();
+#endif
+
+  // Fall back to the default values if the passed-in values are unreasonable.
+  // We want to be able to store at least one full stack.
+  // TODO: Review magic numbers.
+  PowerOfTwo32 capacity =
+      (aCapacity.Value() >=
+       ProfileBufferChunkManager::scExpectedMaximumStackSize / scBytesPerEntry)
+          ? aCapacity
+          : BASE_PROFILER_DEFAULT_ENTRIES;
+  Maybe<double> duration = aDuration;
+
+  if (aDuration && *aDuration <= 0) {
+    duration = Nothing();
+  }
+  double interval = aInterval > 0 ? aInterval : BASE_PROFILER_DEFAULT_INTERVAL;
+
+  ActivePS::Create(aLock, capacity, interval, aFeatures, aFilters, aFilterCount,
+                   duration);
+
+  // Set up profiling for each registered thread, if appropriate.
+  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
+      CorePS::RegisteredThreads(aLock);
+  for (auto& registeredThread : registeredThreads) {
+    RefPtr<ThreadInfo> info = registeredThread->Info();
+
+    if (ActivePS::ShouldProfileThread(aLock, info)) {
+      registeredThread->RacyRegisteredThread().SetIsBeingProfiled(true);
+      ActivePS::AddLiveProfiledThread(aLock, registeredThread.get(),
+                                      MakeUnique<ProfiledThreadData>(info));
+      registeredThread->RacyRegisteredThread().ReinitializeOnResume();
+    }
+  }
+
+  // Setup support for pushing/popping labels in mozglue.
+  RegisterProfilerLabelEnterExit(MozGlueBaseLabelEnter, MozGlueBaseLabelExit);
+
+  // At the very end, set up RacyFeatures.
+  RacyFeatures::SetActive(ActivePS::Features(aLock));
+}
+
+void profiler_start(PowerOfTwo32 aCapacity, double aInterval,
+                    uint32_t aFeatures, const char** aFilters,
+                    uint32_t aFilterCount, const Maybe<double>& aDuration) {
+  LOG("profiler_start");
+
+  SamplerThread* samplerThread = nullptr;
+  {
+    PSAutoLock lock;
+
+    // Initialize if necessary.
+    if (!CorePS::Exists()) {
+      profiler_init(nullptr);
+    }
+
+    // Reset the current state if the profiler is running.
+    if (ActivePS::Exists(lock)) {
+      samplerThread = locked_profiler_stop(lock);
+    }
+
+    locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
+                          aFilterCount, aDuration);
+  }
+
+  // TODO: Install memory counter if it is possible from mozglue.
+  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
+  //   // start counting memory allocations (outside of lock because this may
+  //   call
+  //   // profiler_add_sampled_counter which would attempt to take the lock.)
+  //   mozilla::profiler::install_memory_counter(true);
+  // #endif
+
+  // We do these operations with gPSMutex unlocked. The comments in
+  // profiler_stop() explain why.
+  if (samplerThread) {
+    delete samplerThread;
+  }
+}
+
+void profiler_ensure_started(PowerOfTwo32 aCapacity, double aInterval,
+                             uint32_t aFeatures, const char** aFilters,
+                             uint32_t aFilterCount,
+                             const Maybe<double>& aDuration) {
+  LOG("profiler_ensure_started");
+
+  // bool startedProfiler = false; (See TODO below)
+  SamplerThread* samplerThread = nullptr;
+  {
+    PSAutoLock lock;
+
+    // Initialize if necessary.
+    if (!CorePS::Exists()) {
+      profiler_init(nullptr);
+    }
+
+    if (ActivePS::Exists(lock)) {
+      // The profiler is active.
+      if (!ActivePS::Equals(lock, aCapacity, aDuration, aInterval, aFeatures,
+                            aFilters, aFilterCount)) {
+        // Stop and restart with different settings.
+        samplerThread = locked_profiler_stop(lock);
+        locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
+                              aFilterCount, aDuration);
+        // startedProfiler = true; (See TODO below)
+      }
+    } else {
+      // The profiler is stopped.
+      locked_profiler_start(lock, aCapacity, aInterval, aFeatures, aFilters,
+                            aFilterCount, aDuration);
+      // startedProfiler = true; (See TODO below)
+    }
+  }
+
+  // TODO: Install memory counter if it is possible from mozglue.
+  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
+  //   // start counting memory allocations (outside of lock because this may
+  //   // call profiler_add_sampled_counter which would attempt to take the
+  //   // lock.)
+  //   mozilla::profiler::install_memory_counter(true);
+  // #endif
+
+  // We do these operations with gPSMutex unlocked. The comments in
+  // profiler_stop() explain why.
+  if (samplerThread) {
+    delete samplerThread;
+  }
+}
+
+[[nodiscard]] static SamplerThread* locked_profiler_stop(PSLockRef aLock) {
+  LOG("locked_profiler_stop");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists() && ActivePS::Exists(aLock));
+
+  // At the very start, clear RacyFeatures.
+  RacyFeatures::SetInactive();
+
+  // TODO: Uninstall memory counter if it is possible from mozglue.
+  // #if defined(MOZ_REPLACE_MALLOC) && defined(MOZ_PROFILER_MEMORY)
+  //   mozilla::profiler::install_memory_counter(false);
+  // #endif
+
+  // Remove support for pushing/popping labels in mozglue.
+  RegisterProfilerLabelEnterExit(nullptr, nullptr);
+
+  // Stop sampling live threads.
+  const Vector<LiveProfiledThreadData>& liveProfiledThreads =
+      ActivePS::LiveProfiledThreads(aLock);
+  for (auto& thread : liveProfiledThreads) {
+    RegisteredThread* registeredThread = thread.mRegisteredThread;
+    registeredThread->RacyRegisteredThread().SetIsBeingProfiled(false);
+  }
+
+  // The Stop() call doesn't actually stop Run(); that happens in this
+  // function's caller when the sampler thread is destroyed. Stop() just gives
+  // the SamplerThread a chance to do some cleanup with gPSMutex locked.
+  SamplerThread* samplerThread = ActivePS::Destroy(aLock);
+  samplerThread->Stop(aLock);
+
+  return samplerThread;
+}
+
+void profiler_stop() {
+  LOG("profiler_stop");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  SamplerThread* samplerThread;
+  {
+    PSAutoLock lock;
+
+    if (!ActivePS::Exists(lock)) {
+      return;
+    }
+
+    samplerThread = locked_profiler_stop(lock);
+  }
+
+  // We delete with gPSMutex unlocked. Otherwise we would get a deadlock: we
+  // would be waiting here with gPSMutex locked for SamplerThread::Run() to
+  // return so the join operation within the destructor can complete, but Run()
+  // needs to lock gPSMutex to return.
+  //
+  // Because this call occurs with gPSMutex unlocked, it -- including the final
+  // iteration of Run()'s loop -- must be able detect deactivation and return
+  // in a way that's safe with respect to other gPSMutex-locking operations
+  // that may have occurred in the meantime.
+  delete samplerThread;
+}
+
+bool profiler_is_paused() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return false;
+  }
+
+  return ActivePS::IsPaused(lock);
+}
+
+void profiler_pause() {
+  LOG("profiler_pause");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  {
+    PSAutoLock lock;
+
+    if (!ActivePS::Exists(lock)) {
+      return;
+    }
+
+    RacyFeatures::SetPaused();
+    ActivePS::SetIsPaused(lock, true);
+    ActivePS::Buffer(lock).AddEntry(ProfileBufferEntry::Pause(profiler_time()));
+  }
+}
+
+void profiler_resume() {
+  LOG("profiler_resume");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  {
+    PSAutoLock lock;
+
+    if (!ActivePS::Exists(lock)) {
+      return;
+    }
+
+    ActivePS::Buffer(lock).AddEntry(
+        ProfileBufferEntry::Resume(profiler_time()));
+    ActivePS::SetIsPaused(lock, false);
+    RacyFeatures::SetUnpaused();
+  }
+}
+
+bool profiler_is_sampling_paused() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return false;
+  }
+
+  return ActivePS::IsSamplingPaused(lock);
+}
+
+void profiler_pause_sampling() {
+  LOG("profiler_pause_sampling");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  {
+    PSAutoLock lock;
+
+    if (!ActivePS::Exists(lock)) {
+      return;
+    }
+
+    RacyFeatures::SetSamplingPaused();
+    ActivePS::SetIsSamplingPaused(lock, true);
+    ActivePS::Buffer(lock).AddEntry(
+        ProfileBufferEntry::PauseSampling(profiler_time()));
+  }
+}
+
+void profiler_resume_sampling() {
+  LOG("profiler_resume_sampling");
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  {
+    PSAutoLock lock;
+
+    if (!ActivePS::Exists(lock)) {
+      return;
+    }
+
+    ActivePS::Buffer(lock).AddEntry(
+        ProfileBufferEntry::ResumeSampling(profiler_time()));
+    ActivePS::SetIsSamplingPaused(lock, false);
+    RacyFeatures::SetSamplingUnpaused();
+  }
+}
+
+bool profiler_feature_active(uint32_t aFeature) {
+  // This function runs both on and off the main thread.
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  // This function is hot enough that we use RacyFeatures, not ActivePS.
+  return RacyFeatures::IsActiveWithFeature(aFeature);
+}
+
+void profiler_add_sampled_counter(BaseProfilerCount* aCounter) {
+  DEBUG_LOG("profiler_add_sampled_counter(%s)", aCounter->mLabel);
+  PSAutoLock lock;
+  CorePS::AppendCounter(lock, aCounter);
+}
+
+void profiler_remove_sampled_counter(BaseProfilerCount* aCounter) {
+  DEBUG_LOG("profiler_remove_sampled_counter(%s)", aCounter->mLabel);
+  PSAutoLock lock;
+  // Note: we don't enforce a final sample, though we could do so if the
+  // profiler was active
+  CorePS::RemoveCounter(lock, aCounter);
+}
+
+ProfilingStack* profiler_register_thread(const char* aName,
+                                         void* aGuessStackTop) {
+  DEBUG_LOG("profiler_register_thread(%s)", aName);
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (RegisteredThread* thread = FindCurrentThreadRegisteredThread(lock);
+      thread) {
+    LOG("profiler_register_thread(%s) - thread %d already registered as %s",
+        aName, profiler_current_thread_id(), thread->Info()->Name());
+    // TODO: Use new name. This is currently not possible because the
+    // RegisteredThread's ThreadInfo cannot be changed.
+    // In the meantime, we record a marker that could be used in the frontend.
+    std::string text("Thread ");
+    text += std::to_string(profiler_current_thread_id());
+    text += " \"";
+    text += thread->Info()->Name();
+    text += "\" attempted to re-register as \"";
+    text += aName;
+    text += "\"";
+    BASE_PROFILER_MARKER_TEXT("profiler_register_thread again", OTHER_Profiling,
+                              MarkerThreadId::MainThread(), text);
+
+    return &thread->RacyRegisteredThread().ProfilingStack();
+  }
+
+  void* stackTop = GetStackTop(aGuessStackTop);
+  return locked_register_thread(lock, aName, stackTop);
+}
+
+void profiler_unregister_thread() {
+  if (!CorePS::Exists()) {
+    // This function can be called after the main thread has already shut down.
+    return;
+  }
+
+  PSAutoLock lock;
+
+  RegisteredThread* registeredThread = FindCurrentThreadRegisteredThread(lock);
+  MOZ_RELEASE_ASSERT(registeredThread ==
+                     TLSRegisteredThread::RegisteredThread(lock));
+  if (registeredThread) {
+    RefPtr<ThreadInfo> info = registeredThread->Info();
+
+    DEBUG_LOG("profiler_unregister_thread: %s", info->Name());
+
+    if (ActivePS::Exists(lock)) {
+      ActivePS::UnregisterThread(lock, registeredThread);
+    }
+
+    // Clear the pointer to the RegisteredThread object that we're about to
+    // destroy.
+    TLSRegisteredThread::SetRegisteredThread(lock, nullptr);
+
+    // Remove the thread from the list of registered threads. This deletes the
+    // registeredThread object.
+    CorePS::RemoveRegisteredThread(lock, registeredThread);
+  } else {
+    LOG("profiler_unregister_thread() - thread %d already unregistered",
+        profiler_current_thread_id());
+    // We cannot record a marker on this thread because it was already
+    // unregistered. Send it to the main thread (unless this *is* already the
+    // main thread, which has been unregistered); this may be useful to catch
+    // mismatched register/unregister pairs in Firefox.
+    if (int tid = profiler_current_thread_id();
+        tid != profiler_main_thread_id()) {
+      BASE_PROFILER_MARKER_TEXT("profiler_unregister_thread again",
+                                OTHER_Profiling, MarkerThreadId::MainThread(),
+                                std::to_string(profiler_current_thread_id()));
+    }
+    // There are two ways FindCurrentThreadRegisteredThread() might have failed.
+    //
+    // - TLSRegisteredThread::Init() failed in locked_register_thread().
+    //
+    // - We've already called profiler_unregister_thread() for this thread.
+    //   (Whether or not it should, this does happen in practice.)
+    //
+    // Either way, TLSRegisteredThread should be empty.
+    MOZ_RELEASE_ASSERT(!TLSRegisteredThread::RegisteredThread(lock));
+  }
+}
+
+void profiler_register_page(uint64_t aBrowsingContextID,
+                            uint64_t aInnerWindowID, const std::string& aUrl,
+                            uint64_t aEmbedderInnerWindowID) {
+  DEBUG_LOG("profiler_register_page(%" PRIu64 ", %" PRIu64 ", %s, %" PRIu64 ")",
+            aBrowsingContextID, aInnerWindowID, aUrl.c_str(),
+            aEmbedderInnerWindowID);
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  // When a Browsing context is first loaded, the first url loaded in it will be
+  // about:blank. Because of that, this call keeps the first non-about:blank
+  // registration of window and discards the previous one.
+  RefPtr<PageInformation> pageInfo = new PageInformation(
+      aBrowsingContextID, aInnerWindowID, aUrl, aEmbedderInnerWindowID);
+  CorePS::AppendRegisteredPage(lock, std::move(pageInfo));
+
+  // After appending the given page to CorePS, look for the expired
+  // pages and remove them if there are any.
+  if (ActivePS::Exists(lock)) {
+    ActivePS::DiscardExpiredPages(lock);
+  }
+}
+
+void profiler_unregister_page(uint64_t aRegisteredInnerWindowID) {
+  if (!CorePS::Exists()) {
+    // This function can be called after the main thread has already shut down.
+    return;
+  }
+
+  PSAutoLock lock;
+
+  // During unregistration, if the profiler is active, we have to keep the
+  // page information since there may be some markers associated with the given
+  // page. But if profiler is not active. we have no reason to keep the
+  // page information here because there can't be any marker associated with it.
+  if (ActivePS::Exists(lock)) {
+    ActivePS::UnregisterPage(lock, aRegisteredInnerWindowID);
+  } else {
+    CorePS::RemoveRegisteredPage(lock, aRegisteredInnerWindowID);
+  }
+}
+
+void profiler_clear_all_pages() {
+  if (!CorePS::Exists()) {
+    // This function can be called after the main thread has already shut down.
+    return;
+  }
+
+  {
+    PSAutoLock lock;
+    CorePS::ClearRegisteredPages(lock);
+    if (ActivePS::Exists(lock)) {
+      ActivePS::ClearUnregisteredPages(lock);
+    }
+  }
+}
+
+void profiler_thread_sleep() {
+  // This function runs both on and off the main thread.
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  RacyRegisteredThread* racyRegisteredThread =
+      TLSRegisteredThread::RacyRegisteredThread();
+  if (!racyRegisteredThread) {
+    return;
+  }
+
+  racyRegisteredThread->SetSleeping();
+}
+
+void profiler_thread_wake() {
+  // This function runs both on and off the main thread.
+
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  RacyRegisteredThread* racyRegisteredThread =
+      TLSRegisteredThread::RacyRegisteredThread();
+  if (!racyRegisteredThread) {
+    return;
+  }
+
+  racyRegisteredThread->SetAwake();
+}
+
+bool detail::IsThreadBeingProfiled() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  const RacyRegisteredThread* racyRegisteredThread =
+      TLSRegisteredThread::RacyRegisteredThread();
+  return racyRegisteredThread && racyRegisteredThread->IsBeingProfiled();
+}
+
+bool profiler_thread_is_sleeping() {
+  MOZ_RELEASE_ASSERT(profiler_is_main_thread());
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  RacyRegisteredThread* racyRegisteredThread =
+      TLSRegisteredThread::RacyRegisteredThread();
+  if (!racyRegisteredThread) {
+    return false;
+  }
+  return racyRegisteredThread->IsSleeping();
+}
+
+double profiler_time() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  TimeDuration delta = TimeStamp::NowUnfuzzed() - CorePS::ProcessStartTime();
+  return delta.ToMilliseconds();
+}
+
+bool profiler_capture_backtrace_into(ProfileChunkedBuffer& aChunkedBuffer) {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  PSAutoLock lock;
+
+  if (!ActivePS::Exists(lock)) {
+    return false;
+  }
+
+  RegisteredThread* registeredThread =
+      TLSRegisteredThread::RegisteredThread(lock);
+  if (!registeredThread) {
+    MOZ_ASSERT(registeredThread);
+    return false;
+  }
+
+  ProfileBuffer profileBuffer(aChunkedBuffer);
+
+  Registers regs;
+#if defined(HAVE_NATIVE_UNWIND)
+  regs.SyncPopulate();
+#else
+  regs.Clear();
+#endif
+
+  DoSyncSample(lock, *registeredThread, TimeStamp::NowUnfuzzed(), regs,
+               profileBuffer);
+
+  return true;
+}
+
+UniquePtr<ProfileChunkedBuffer> profiler_capture_backtrace() {
+  MOZ_RELEASE_ASSERT(CorePS::Exists());
+
+  // Quick is-active check before allocating a buffer.
+  if (!profiler_is_active()) {
+    return nullptr;
+  }
+
+  auto buffer = MakeUnique<ProfileChunkedBuffer>(
+      ProfileChunkedBuffer::ThreadSafety::WithoutMutex,
+      MakeUnique<ProfileBufferChunkManagerSingle>(
+          ProfileBufferChunkManager::scExpectedMaximumStackSize));
+
+  if (!profiler_capture_backtrace_into(*buffer)) {
+    return nullptr;
+  }
+
+  return buffer;
+}
+
+UniqueProfilerBacktrace profiler_get_backtrace() {
+  UniquePtr<ProfileChunkedBuffer> buffer = profiler_capture_backtrace();
+
+  if (!buffer) {
+    return nullptr;
+  }
+
+  return UniqueProfilerBacktrace(
+      new ProfilerBacktrace("SyncProfile", std::move(buffer)));
+}
+
+void ProfilerBacktraceDestructor::operator()(ProfilerBacktrace* aBacktrace) {
+  delete aBacktrace;
+}
+
+bool profiler_is_locked_on_current_thread() {
+  // This function is used to help users avoid calling `profiler_...` functions
+  // when the profiler may already have a lock in place, which would prevent a
+  // 2nd recursive lock (resulting in a crash or a never-ending wait).
+  // So we must return `true` for any of:
+  // - The main profiler mutex, used by most functions, and/or
+  // - The buffer mutex, used directly in some functions without locking the
+  //   main mutex, e.g., marker-related functions.
+  return PSAutoLock::IsLockedOnCurrentThread() ||
+         CorePS::CoreBuffer().IsThreadSafeAndLockedOnCurrentThread();
+}
+
+// This is a simplified version of profiler_add_marker that can be easily passed
+// into the JS engine.
+void profiler_add_js_marker(const char* aMarkerName, const char* aMarkerText) {
+  BASE_PROFILER_MARKER_TEXT(
+      ProfilerString8View::WrapNullTerminatedString(aMarkerName), JS, {},
+      ProfilerString8View::WrapNullTerminatedString(aMarkerText));
+}
+
+// NOTE: aCollector's methods will be called while the target thread is paused.
+// Doing things in those methods like allocating -- which may try to claim
+// locks -- is a surefire way to deadlock.
+void profiler_suspend_and_sample_thread(int aThreadId, uint32_t aFeatures,
+                                        ProfilerStackCollector& aCollector,
+                                        bool aSampleNative /* = true */) {
+  // Lock the profiler mutex
+  PSAutoLock lock;
+
+  const Vector<UniquePtr<RegisteredThread>>& registeredThreads =
+      CorePS::RegisteredThreads(lock);
+  for (auto& thread : registeredThreads) {
+    RefPtr<ThreadInfo> info = thread->Info();
+    RegisteredThread& registeredThread = *thread.get();
+
+    if (info->ThreadId() == aThreadId) {
+      if (info->IsMainThread()) {
+        aCollector.SetIsMainThread();
+      }
+
+      // Allocate the space for the native stack
+      NativeStack nativeStack;
+
+      // Suspend, sample, and then resume the target thread.
+      Sampler sampler(lock);
+      TimeStamp now = TimeStamp::NowUnfuzzed();
+      sampler.SuspendAndSampleAndResumeThread(
+          lock, registeredThread, now,
+          [&](const Registers& aRegs, const TimeStamp& aNow) {
+            // The target thread is now suspended. Collect a native
+            // backtrace, and call the callback.
+            bool isSynchronous = false;
+#if defined(HAVE_FASTINIT_NATIVE_UNWIND)
+            if (aSampleNative) {
+          // We can only use FramePointerStackWalk or MozStackWalk from
+          // suspend_and_sample_thread as other stackwalking methods may not be
+          // initialized.
+#  if defined(USE_FRAME_POINTER_STACK_WALK)
+              DoFramePointerBacktrace(lock, registeredThread, aRegs,
+                                      nativeStack);
+#  elif defined(USE_MOZ_STACK_WALK)
+              DoMozStackWalkBacktrace(lock, registeredThread, aRegs,
+                                      nativeStack);
+#  else
+#    error "Invalid configuration"
+#  endif
+
+              MergeStacks(aFeatures, isSynchronous, registeredThread, aRegs,
+                          nativeStack, aCollector);
+            } else
+#endif
+            {
+              MergeStacks(aFeatures, isSynchronous, registeredThread, aRegs,
+                          nativeStack, aCollector);
+
+              if (ProfilerFeature::HasLeaf(aFeatures)) {
+                aCollector.CollectNativeLeafAddr((void*)aRegs.mPC);
+              }
+            }
+          });
+
+      // NOTE: Make sure to disable the sampler before it is destroyed, in case
+      // the profiler is running at the same time.
+      sampler.Disable(lock);
+      break;
+    }
+  }
+}
+
+// END externally visible functions
+////////////////////////////////////////////////////////////////////////
+
+}  // namespace baseprofiler
+}  // namespace mozilla