Libsanitizer: merge from master.

Merged from revision b638b63b99d66786cb37336292604a2ae3490cfd.

The patch successfully bootstraps on x86_64-linux-gnu and
ppc64le-linux-gnu. I also tested ppc64-linux-gnu that exposed:
https://reviews.llvm.org/D80864 (which is fixed on master).

Abidiff looks happy and I made UBSAN and ASAN bootstrap on
x86_64-linux-gnu.

I'm planning to do merge from master twice a year, once now and
next time short before stage1 closes.

I am going to install the patches as merge from master is obvious
and I haven't made anything special.

libsanitizer/ChangeLog:

	* MERGE: Merge from master.

16 files changed, 589 insertions, 140 deletions

diff --git a/libsanitizer/lsan/lsan.cpp b/libsanitizer/lsan/lsan.cpp
index 4ce0304..80a6e2f 100644
--- a/libsanitizer/lsan/lsan.cpp
+++ b/libsanitizer/lsan/lsan.cpp
@@ -15,7 +15,6 @@
 
 #include "sanitizer_common/sanitizer_flags.h"
 #include "sanitizer_common/sanitizer_flag_parser.h"
-#include "sanitizer_common/sanitizer_stacktrace.h"
 #include "lsan_allocator.h"
 #include "lsan_common.h"
 #include "lsan_thread.h"
@@ -87,17 +86,6 @@ static void InitializeFlags() {
   __sanitizer_set_report_path(common_flags()->log_path);
 }
 
-static void OnStackUnwind(const SignalContext &sig, const void *,
-                          BufferedStackTrace *stack) {
-  stack->Unwind(StackTrace::GetNextInstructionPc(sig.pc), sig.bp, sig.context,
-                common_flags()->fast_unwind_on_fatal);
-}
-
-static void LsanOnDeadlySignal(int signo, void *siginfo, void *context) {
-  HandleDeadlySignal(siginfo, context, GetCurrentThread(), &OnStackUnwind,
-                     nullptr);
-}
-
 extern "C" void __lsan_init() {
   CHECK(!lsan_init_is_running);
   if (lsan_inited)
@@ -114,10 +102,7 @@ extern "C" void __lsan_init() {
   InitializeInterceptors();
   InitializeThreadRegistry();
   InstallDeadlySignalHandlers(LsanOnDeadlySignal);
-  u32 tid = ThreadCreate(0, 0, true);
-  CHECK_EQ(tid, 0);
-  ThreadStart(tid, GetTid());
-  SetCurrentThread(tid);
+  InitializeMainThread();
 
   if (common_flags()->detect_leaks && common_flags()->leak_check_at_exit)
     Atexit(DoLeakCheck);
diff --git a/libsanitizer/lsan/lsan.h b/libsanitizer/lsan/lsan.h
index 9904ada..1e82ad7 100644
--- a/libsanitizer/lsan/lsan.h
+++ b/libsanitizer/lsan/lsan.h
@@ -12,6 +12,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "lsan_thread.h"
+#if SANITIZER_POSIX
+#include "lsan_posix.h"
+#elif SANITIZER_FUCHSIA
+#include "lsan_fuchsia.h"
+#endif
 #include "sanitizer_common/sanitizer_flags.h"
 #include "sanitizer_common/sanitizer_stacktrace.h"
 
@@ -33,6 +38,7 @@ namespace __lsan {
 
 void InitializeInterceptors();
 void ReplaceSystemMalloc();
+void LsanOnDeadlySignal(int signo, void *siginfo, void *context);
 
 #define ENSURE_LSAN_INITED do {   \
   CHECK(!lsan_init_is_running);   \
diff --git a/libsanitizer/lsan/lsan_allocator.h b/libsanitizer/lsan/lsan_allocator.h
index e139709..bda9d8c 100644
--- a/libsanitizer/lsan/lsan_allocator.h
+++ b/libsanitizer/lsan/lsan_allocator.h
@@ -66,7 +66,10 @@ template <typename AddressSpaceView>
 using PrimaryAllocatorASVT = SizeClassAllocator32<AP32<AddressSpaceView>>;
 using PrimaryAllocator = PrimaryAllocatorASVT<LocalAddressSpaceView>;
 #elif defined(__x86_64__) || defined(__powerpc64__)
-# if defined(__powerpc64__)
+# if SANITIZER_FUCHSIA
+const uptr kAllocatorSpace = ~(uptr)0;
+const uptr kAllocatorSize  =  0x40000000000ULL;  // 4T.
+# elif defined(__powerpc64__)
 const uptr kAllocatorSpace = 0xa0000000000ULL;
 const uptr kAllocatorSize  = 0x20000000000ULL;  // 2T.
 # else
diff --git a/libsanitizer/lsan/lsan_common.cpp b/libsanitizer/lsan/lsan_common.cpp
index 9ff9f4c..32ea4e8 100644
--- a/libsanitizer/lsan/lsan_common.cpp
+++ b/libsanitizer/lsan/lsan_common.cpp
@@ -211,6 +211,13 @@ void ForEachExtraStackRangeCb(uptr begin, uptr end, void* arg) {
   ScanRangeForPointers(begin, end, frontier, "FAKE STACK", kReachable);
 }
 
+#if SANITIZER_FUCHSIA
+
+// Fuchsia handles all threads together with its own callback.
+static void ProcessThreads(SuspendedThreadsList const &, Frontier *) {}
+
+#else
+
 // Scans thread data (stacks and TLS) for heap pointers.
 static void ProcessThreads(SuspendedThreadsList const &suspended_threads,
                            Frontier *frontier) {
@@ -308,6 +315,8 @@ static void ProcessThreads(SuspendedThreadsList const &suspended_threads,
   }
 }
 
+#endif  // SANITIZER_FUCHSIA
+
 void ScanRootRegion(Frontier *frontier, const RootRegion &root_region,
                     uptr region_begin, uptr region_end, bool is_readable) {
   uptr intersection_begin = Max(root_region.begin, region_begin);
@@ -443,25 +452,23 @@ void ProcessPC(Frontier *frontier) {
 }
 
 // Sets the appropriate tag on each chunk.
-static void ClassifyAllChunks(SuspendedThreadsList const &suspended_threads) {
-  // Holds the flood fill frontier.
-  Frontier frontier;
-
-  ForEachChunk(CollectIgnoredCb, &frontier);
-  ProcessGlobalRegions(&frontier);
-  ProcessThreads(suspended_threads, &frontier);
-  ProcessRootRegions(&frontier);
-  FloodFillTag(&frontier, kReachable);
+static void ClassifyAllChunks(SuspendedThreadsList const &suspended_threads,
+                              Frontier *frontier) {
+  ForEachChunk(CollectIgnoredCb, frontier);
+  ProcessGlobalRegions(frontier);
+  ProcessThreads(suspended_threads, frontier);
+  ProcessRootRegions(frontier);
+  FloodFillTag(frontier, kReachable);
 
-  CHECK_EQ(0, frontier.size());
-  ProcessPC(&frontier);
+  CHECK_EQ(0, frontier->size());
+  ProcessPC(frontier);
 
   // The check here is relatively expensive, so we do this in a separate flood
   // fill. That way we can skip the check for chunks that are reachable
   // otherwise.
   LOG_POINTERS("Processing platform-specific allocations.\n");
-  ProcessPlatformSpecificAllocations(&frontier);
-  FloodFillTag(&frontier, kReachable);
+  ProcessPlatformSpecificAllocations(frontier);
+  FloodFillTag(frontier, kReachable);
 
   // Iterate over leaked chunks and mark those that are reachable from other
   // leaked chunks.
@@ -521,11 +528,6 @@ static void PrintMatchedSuppressions() {
   Printf("%s\n\n", line);
 }
 
-struct CheckForLeaksParam {
-  bool success;
-  LeakReport leak_report;
-};
-
 static void ReportIfNotSuspended(ThreadContextBase *tctx, void *arg) {
   const InternalMmapVector<tid_t> &suspended_threads =
       *(const InternalMmapVector<tid_t> *)arg;
@@ -538,6 +540,14 @@ static void ReportIfNotSuspended(ThreadContextBase *tctx, void *arg) {
   }
 }
 
+#if SANITIZER_FUCHSIA
+
+// Fuchsia provides a libc interface that guarantees all threads are
+// covered, and SuspendedThreadList is never really used.
+static void ReportUnsuspendedThreads(const SuspendedThreadsList &) {}
+
+#else  // !SANITIZER_FUCHSIA
+
 static void ReportUnsuspendedThreads(
     const SuspendedThreadsList &suspended_threads) {
   InternalMmapVector<tid_t> threads(suspended_threads.ThreadCount());
@@ -550,13 +560,15 @@ static void ReportUnsuspendedThreads(
       &ReportIfNotSuspended, &threads);
 }
 
+#endif  // !SANITIZER_FUCHSIA
+
 static void CheckForLeaksCallback(const SuspendedThreadsList &suspended_threads,
                                   void *arg) {
   CheckForLeaksParam *param = reinterpret_cast<CheckForLeaksParam *>(arg);
   CHECK(param);
   CHECK(!param->success);
   ReportUnsuspendedThreads(suspended_threads);
-  ClassifyAllChunks(suspended_threads);
+  ClassifyAllChunks(suspended_threads, &param->frontier);
   ForEachChunk(CollectLeaksCb, &param->leak_report);
   // Clean up for subsequent leak checks. This assumes we did not overwrite any
   // kIgnored tags.
@@ -569,7 +581,6 @@ static bool CheckForLeaks() {
       return false;
   EnsureMainThreadIDIsCorrect();
   CheckForLeaksParam param;
-  param.success = false;
   LockStuffAndStopTheWorld(CheckForLeaksCallback, &param);
 
   if (!param.success) {
diff --git a/libsanitizer/lsan/lsan_common.h b/libsanitizer/lsan/lsan_common.h
index d24abe3..6252d52 100644
--- a/libsanitizer/lsan/lsan_common.h
+++ b/libsanitizer/lsan/lsan_common.h
@@ -40,7 +40,7 @@
 #elif defined(__arm__) && \
     SANITIZER_LINUX && !SANITIZER_ANDROID
 #define CAN_SANITIZE_LEAKS 1
-#elif SANITIZER_NETBSD
+#elif SANITIZER_NETBSD || SANITIZER_FUCHSIA
 #define CAN_SANITIZE_LEAKS 1
 #else
 #define CAN_SANITIZE_LEAKS 0
@@ -126,12 +126,24 @@ struct RootRegion {
   uptr size;
 };
 
+// LockStuffAndStopTheWorld can start to use Scan* calls to collect into
+// this Frontier vector before the StopTheWorldCallback actually runs.
+// This is used when the OS has a unified callback API for suspending
+// threads and enumerating roots.
+struct CheckForLeaksParam {
+  Frontier frontier;
+  LeakReport leak_report;
+  bool success = false;
+};
+
 InternalMmapVector<RootRegion> const *GetRootRegions();
 void ScanRootRegion(Frontier *frontier, RootRegion const &region,
                     uptr region_begin, uptr region_end, bool is_readable);
+void ForEachExtraStackRangeCb(uptr begin, uptr end, void* arg);
 // Run stoptheworld while holding any platform-specific locks, as well as the
 // allocator and thread registry locks.
-void LockStuffAndStopTheWorld(StopTheWorldCallback callback, void* argument);
+void LockStuffAndStopTheWorld(StopTheWorldCallback callback,
+                              CheckForLeaksParam* argument);
 
 void ScanRangeForPointers(uptr begin, uptr end,
                           Frontier *frontier,
@@ -211,6 +223,7 @@ ThreadRegistry *GetThreadRegistryLocked();
 bool GetThreadRangesLocked(tid_t os_id, uptr *stack_begin, uptr *stack_end,
                            uptr *tls_begin, uptr *tls_end, uptr *cache_begin,
                            uptr *cache_end, DTLS **dtls);
+void GetAllThreadAllocatorCachesLocked(InternalMmapVector<uptr> *caches);
 void ForEachExtraStackRange(tid_t os_id, RangeIteratorCallback callback,
                             void *arg);
 // If called from the main thread, updates the main thread's TID in the thread
diff --git a/libsanitizer/lsan/lsan_common_fuchsia.cpp b/libsanitizer/lsan/lsan_common_fuchsia.cpp
new file mode 100644
index 0000000..caedbf1
--- /dev/null
+++ b/libsanitizer/lsan/lsan_common_fuchsia.cpp
@@ -0,0 +1,166 @@
+//=-- lsan_common_fuchsia.cpp --------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This file is a part of LeakSanitizer.
+// Implementation of common leak checking functionality. Fuchsia-specific code.
+//
+//===---------------------------------------------------------------------===//
+
+#include "lsan_common.h"
+#include "sanitizer_common/sanitizer_platform.h"
+
+#if CAN_SANITIZE_LEAKS && SANITIZER_FUCHSIA
+#include <zircon/sanitizer.h>
+
+#include "lsan_allocator.h"
+#include "sanitizer_common/sanitizer_flags.h"
+#include "sanitizer_common/sanitizer_thread_registry.h"
+
+// Ensure that the Zircon system ABI is linked in.
+#pragma comment(lib, "zircon")
+
+namespace __lsan {
+
+void InitializePlatformSpecificModules() {}
+
+LoadedModule *GetLinker() { return nullptr; }
+
+__attribute__((tls_model("initial-exec"))) THREADLOCAL int disable_counter;
+bool DisabledInThisThread() { return disable_counter > 0; }
+void DisableInThisThread() { disable_counter++; }
+void EnableInThisThread() {
+  if (disable_counter == 0) {
+    DisableCounterUnderflow();
+  }
+  disable_counter--;
+}
+
+// There is nothing left to do after the globals callbacks.
+void ProcessGlobalRegions(Frontier *frontier) {}
+
+// Nothing to do here.
+void ProcessPlatformSpecificAllocations(Frontier *frontier) {}
+
+// On Fuchsia, we can intercept _Exit gracefully, and return a failing exit
+// code if required at that point.  Calling Die() here is undefined
+// behavior and causes rare race conditions.
+void HandleLeaks() {}
+
+int ExitHook(int status) {
+  return status == 0 && HasReportedLeaks() ? common_flags()->exitcode : status;
+}
+
+void LockStuffAndStopTheWorld(StopTheWorldCallback callback,
+                              CheckForLeaksParam *argument) {
+  LockThreadRegistry();
+  LockAllocator();
+
+  struct Params {
+    InternalMmapVector<uptr> allocator_caches;
+    StopTheWorldCallback callback;
+    CheckForLeaksParam *argument;
+  } params = {{}, callback, argument};
+
+  // Callback from libc for globals (data/bss modulo relro), when enabled.
+  auto globals = +[](void *chunk, size_t size, void *data) {
+    auto params = static_cast<const Params *>(data);
+    uptr begin = reinterpret_cast<uptr>(chunk);
+    uptr end = begin + size;
+    ScanGlobalRange(begin, end, &params->argument->frontier);
+  };
+
+  // Callback from libc for thread stacks.
+  auto stacks = +[](void *chunk, size_t size, void *data) {
+    auto params = static_cast<const Params *>(data);
+    uptr begin = reinterpret_cast<uptr>(chunk);
+    uptr end = begin + size;
+    ScanRangeForPointers(begin, end, &params->argument->frontier, "STACK",
+                         kReachable);
+  };
+
+  // Callback from libc for thread registers.
+  auto registers = +[](void *chunk, size_t size, void *data) {
+    auto params = static_cast<const Params *>(data);
+    uptr begin = reinterpret_cast<uptr>(chunk);
+    uptr end = begin + size;
+    ScanRangeForPointers(begin, end, &params->argument->frontier, "REGISTERS",
+                         kReachable);
+  };
+
+  if (flags()->use_tls) {
+    // Collect the allocator cache range from each thread so these
+    // can all be excluded from the reported TLS ranges.
+    GetAllThreadAllocatorCachesLocked(&params.allocator_caches);
+    __sanitizer::Sort(params.allocator_caches.data(),
+                      params.allocator_caches.size());
+  }
+
+  // Callback from libc for TLS regions.  This includes thread_local
+  // variables as well as C11 tss_set and POSIX pthread_setspecific.
+  auto tls = +[](void *chunk, size_t size, void *data) {
+    auto params = static_cast<const Params *>(data);
+    uptr begin = reinterpret_cast<uptr>(chunk);
+    uptr end = begin + size;
+    auto i = __sanitizer::InternalLowerBound(params->allocator_caches, 0,
+                                             params->allocator_caches.size(),
+                                             begin, CompareLess<uptr>());
+    if (i < params->allocator_caches.size() &&
+        params->allocator_caches[i] >= begin &&
+        end - params->allocator_caches[i] <= sizeof(AllocatorCache)) {
+      // Split the range in two and omit the allocator cache within.
+      ScanRangeForPointers(begin, params->allocator_caches[i],
+                           &params->argument->frontier, "TLS", kReachable);
+      uptr begin2 = params->allocator_caches[i] + sizeof(AllocatorCache);
+      ScanRangeForPointers(begin2, end, &params->argument->frontier, "TLS",
+                           kReachable);
+    } else {
+      ScanRangeForPointers(begin, end, &params->argument->frontier, "TLS",
+                           kReachable);
+    }
+  };
+
+  // This stops the world and then makes callbacks for various memory regions.
+  // The final callback is the last thing before the world starts up again.
+  __sanitizer_memory_snapshot(
+      flags()->use_globals ? globals : nullptr,
+      flags()->use_stacks ? stacks : nullptr,
+      flags()->use_registers ? registers : nullptr,
+      flags()->use_tls ? tls : nullptr,
+      [](zx_status_t, void *data) {
+        auto params = static_cast<const Params *>(data);
+
+        // We don't use the thread registry at all for enumerating the threads
+        // and their stacks, registers, and TLS regions.  So use it separately
+        // just for the allocator cache, and to call ForEachExtraStackRange,
+        // which ASan needs.
+        if (flags()->use_stacks) {
+          GetThreadRegistryLocked()->RunCallbackForEachThreadLocked(
+              [](ThreadContextBase *tctx, void *arg) {
+                ForEachExtraStackRange(tctx->os_id, ForEachExtraStackRangeCb,
+                                       arg);
+              },
+              &params->argument->frontier);
+        }
+
+        params->callback({}, params->argument);
+      },
+      &params);
+
+  UnlockAllocator();
+  UnlockThreadRegistry();
+}
+
+}  // namespace __lsan
+
+// This is declared (in extern "C") by <zircon/sanitizer.h>.
+// _Exit calls this directly to intercept and change the status value.
+int __sanitizer_process_exit_hook(int status) {
+  return __lsan::ExitHook(status);
+}
+
+#endif
diff --git a/libsanitizer/lsan/lsan_common_linux.cpp b/libsanitizer/lsan/lsan_common_linux.cpp
index ea1a4a2..c97ef315 100644
--- a/libsanitizer/lsan/lsan_common_linux.cpp
+++ b/libsanitizer/lsan/lsan_common_linux.cpp
@@ -134,7 +134,8 @@ static int LockStuffAndStopTheWorldCallback(struct dl_phdr_info *info,
 // while holding the libdl lock in the parent thread, we can safely reenter it
 // in the tracer. The solution is to run stoptheworld from a dl_iterate_phdr()
 // callback in the parent thread.
-void LockStuffAndStopTheWorld(StopTheWorldCallback callback, void *argument) {
+void LockStuffAndStopTheWorld(StopTheWorldCallback callback,
+                              CheckForLeaksParam *argument) {
   DoStopTheWorldParam param = {callback, argument};
   dl_iterate_phdr(LockStuffAndStopTheWorldCallback, &param);
 }
diff --git a/libsanitizer/lsan/lsan_common_mac.cpp b/libsanitizer/lsan/lsan_common_mac.cpp
index c1804e9..8516a17 100644
--- a/libsanitizer/lsan/lsan_common_mac.cpp
+++ b/libsanitizer/lsan/lsan_common_mac.cpp
@@ -193,7 +193,8 @@ void ProcessPlatformSpecificAllocations(Frontier *frontier) {
 // causes rare race conditions.
 void HandleLeaks() {}
 
-void LockStuffAndStopTheWorld(StopTheWorldCallback callback, void *argument) {
+void LockStuffAndStopTheWorld(StopTheWorldCallback callback,
+                              CheckForLeaksParam *argument) {
   LockThreadRegistry();
   LockAllocator();
   StopTheWorld(callback, argument);
diff --git a/libsanitizer/lsan/lsan_fuchsia.cpp b/libsanitizer/lsan/lsan_fuchsia.cpp
new file mode 100644
index 0000000..40e65c6
--- /dev/null
+++ b/libsanitizer/lsan/lsan_fuchsia.cpp
@@ -0,0 +1,123 @@
+//=-- lsan_fuchsia.cpp ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This file is a part of LeakSanitizer.
+// Standalone LSan RTL code specific to Fuchsia.
+//
+//===---------------------------------------------------------------------===//
+
+#include "sanitizer_common/sanitizer_platform.h"
+
+#if SANITIZER_FUCHSIA
+#include <zircon/sanitizer.h>
+
+#include "lsan.h"
+#include "lsan_allocator.h"
+
+using namespace __lsan;
+
+namespace __lsan {
+
+void LsanOnDeadlySignal(int signo, void *siginfo, void *context) {}
+
+ThreadContext::ThreadContext(int tid) : ThreadContextLsanBase(tid) {}
+
+struct OnCreatedArgs {
+  uptr stack_begin, stack_end;
+};
+
+// On Fuchsia, the stack bounds of a new thread are available before
+// the thread itself has started running.
+void ThreadContext::OnCreated(void *arg) {
+  // Stack bounds passed through from __sanitizer_before_thread_create_hook
+  // or InitializeMainThread.
+  auto args = reinterpret_cast<const OnCreatedArgs *>(arg);
+  stack_begin_ = args->stack_begin;
+  stack_end_ = args->stack_end;
+}
+
+struct OnStartedArgs {
+  uptr cache_begin, cache_end;
+};
+
+void ThreadContext::OnStarted(void *arg) {
+  auto args = reinterpret_cast<const OnStartedArgs *>(arg);
+  cache_begin_ = args->cache_begin;
+  cache_end_ = args->cache_end;
+}
+
+void ThreadStart(u32 tid) {
+  OnStartedArgs args;
+  GetAllocatorCacheRange(&args.cache_begin, &args.cache_end);
+  CHECK_EQ(args.cache_end - args.cache_begin, sizeof(AllocatorCache));
+  ThreadContextLsanBase::ThreadStart(tid, GetTid(), ThreadType::Regular, &args);
+}
+
+void InitializeMainThread() {
+  OnCreatedArgs args;
+  __sanitizer::GetThreadStackTopAndBottom(true, &args.stack_end,
+                                          &args.stack_begin);
+  u32 tid = ThreadCreate(0, GetThreadSelf(), true, &args);
+  CHECK_EQ(tid, 0);
+  ThreadStart(tid);
+}
+
+void GetAllThreadAllocatorCachesLocked(InternalMmapVector<uptr> *caches) {
+  GetThreadRegistryLocked()->RunCallbackForEachThreadLocked(
+      [](ThreadContextBase *tctx, void *arg) {
+        auto ctx = static_cast<ThreadContext *>(tctx);
+        static_cast<decltype(caches)>(arg)->push_back(ctx->cache_begin());
+      },
+      caches);
+}
+
+}  // namespace __lsan
+
+// These are declared (in extern "C") by <zircon/sanitizer.h>.
+// The system runtime will call our definitions directly.
+
+// This is called before each thread creation is attempted.  So, in
+// its first call, the calling thread is the initial and sole thread.
+void *__sanitizer_before_thread_create_hook(thrd_t thread, bool detached,
+                                            const char *name, void *stack_base,
+                                            size_t stack_size) {
+  uptr user_id = reinterpret_cast<uptr>(thread);
+  ENSURE_LSAN_INITED;
+  EnsureMainThreadIDIsCorrect();
+  OnCreatedArgs args;
+  args.stack_begin = reinterpret_cast<uptr>(stack_base);
+  args.stack_end = args.stack_begin + stack_size;
+  u32 parent_tid = GetCurrentThread();
+  u32 tid = ThreadCreate(parent_tid, user_id, detached, &args);
+  return reinterpret_cast<void *>(static_cast<uptr>(tid));
+}
+
+// This is called after creating a new thread (in the creating thread),
+// with the pointer returned by __sanitizer_before_thread_create_hook (above).
+void __sanitizer_thread_create_hook(void *hook, thrd_t thread, int error) {
+  u32 tid = static_cast<u32>(reinterpret_cast<uptr>(hook));
+  // On success, there is nothing to do here.
+  if (error != thrd_success) {
+    // Clean up the thread registry for the thread creation that didn't happen.
+    GetThreadRegistryLocked()->FinishThread(tid);
+  }
+}
+
+// This is called in the newly-created thread before it runs anything else,
+// with the pointer returned by __sanitizer_before_thread_create_hook (above).
+void __sanitizer_thread_start_hook(void *hook, thrd_t self) {
+  u32 tid = static_cast<u32>(reinterpret_cast<uptr>(hook));
+  ThreadStart(tid);
+}
+
+// Each thread runs this just before it exits,
+// with the pointer returned by BeforeThreadCreateHook (above).
+// All per-thread destructors have already been called.
+void __sanitizer_thread_exit_hook(void *hook, thrd_t self) { ThreadFinish(); }
+
+#endif  // SANITIZER_FUCHSIA
diff --git a/libsanitizer/lsan/lsan_fuchsia.h b/libsanitizer/lsan/lsan_fuchsia.h
new file mode 100644
index 0000000..65d20ea
--- /dev/null
+++ b/libsanitizer/lsan/lsan_fuchsia.h
@@ -0,0 +1,35 @@
+//=-- lsan_fuchsia.h ---------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This file is a part of LeakSanitizer.
+// Standalone LSan RTL code specific to Fuchsia.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef LSAN_FUCHSIA_H
+#define LSAN_FUCHSIA_H
+
+#include "lsan_thread.h"
+#include "sanitizer_common/sanitizer_platform.h"
+
+#if !SANITIZER_FUCHSIA
+#error "lsan_fuchsia.h is used only on Fuchsia systems (SANITIZER_FUCHSIA)"
+#endif
+
+namespace __lsan {
+
+class ThreadContext : public ThreadContextLsanBase {
+ public:
+  explicit ThreadContext(int tid);
+  void OnCreated(void *arg) override;
+  void OnStarted(void *arg) override;
+};
+
+}  // namespace __lsan
+
+#endif  // LSAN_FUCHSIA_H
diff --git a/libsanitizer/lsan/lsan_interceptors.cpp b/libsanitizer/lsan/lsan_interceptors.cpp
index f642bb8..9ce9b78 100644
--- a/libsanitizer/lsan/lsan_interceptors.cpp
+++ b/libsanitizer/lsan/lsan_interceptors.cpp
@@ -22,7 +22,9 @@
 #include "sanitizer_common/sanitizer_platform_interceptors.h"
 #include "sanitizer_common/sanitizer_platform_limits_netbsd.h"
 #include "sanitizer_common/sanitizer_platform_limits_posix.h"
+#if SANITIZER_POSIX
 #include "sanitizer_common/sanitizer_posix.h"
+#endif
 #include "sanitizer_common/sanitizer_tls_get_addr.h"
 #include "lsan.h"
 #include "lsan_allocator.h"
@@ -61,6 +63,9 @@ INTERCEPTOR(void, free, void *p) {
 }
 
 INTERCEPTOR(void*, calloc, uptr nmemb, uptr size) {
+  // This hack is not required for Fuchsia because there are no dlsym calls
+  // involved in setting up interceptors.
+#if !SANITIZER_FUCHSIA
   if (lsan_init_is_running) {
     // Hack: dlsym calls calloc before REAL(calloc) is retrieved from dlsym.
     const uptr kCallocPoolSize = 1024;
@@ -72,6 +77,7 @@ INTERCEPTOR(void*, calloc, uptr nmemb, uptr size) {
     CHECK(allocated < kCallocPoolSize);
     return mem;
   }
+#endif  // !SANITIZER_FUCHSIA
   ENSURE_LSAN_INITED;
   GET_STACK_TRACE_MALLOC;
   return lsan_calloc(nmemb, size, stack);
@@ -100,7 +106,7 @@ INTERCEPTOR(void*, valloc, uptr size) {
   GET_STACK_TRACE_MALLOC;
   return lsan_valloc(size, stack);
 }
-#endif
+#endif  // !SANITIZER_MAC
 
 #if SANITIZER_INTERCEPT_MEMALIGN
 INTERCEPTOR(void*, memalign, uptr alignment, uptr size) {
@@ -307,7 +313,7 @@ INTERCEPTOR(void, _ZdaPvRKSt9nothrow_t, void *ptr, std::nothrow_t const&)
 
 ///// Thread initialization and finalization. /////
 
-#if !SANITIZER_NETBSD && !SANITIZER_FREEBSD
+#if !SANITIZER_NETBSD && !SANITIZER_FREEBSD && !SANITIZER_FUCHSIA
 static unsigned g_thread_finalize_key;
 
 static void thread_finalize(void *v) {
@@ -394,6 +400,8 @@ INTERCEPTOR(char *, strerror, int errnum) {
 #define LSAN_MAYBE_INTERCEPT_STRERROR
 #endif
 
+#if SANITIZER_POSIX
+
 struct ThreadParam {
   void *(*callback)(void *arg);
   void *param;
@@ -416,7 +424,6 @@ extern "C" void *__lsan_thread_start_func(void *arg) {
   int tid = 0;
   while ((tid = atomic_load(&p->tid, memory_order_acquire)) == 0)
     internal_sched_yield();
-  SetCurrentThread(tid);
   ThreadStart(tid, GetTid());
   atomic_store(&p->tid, 0, memory_order_release);
   return callback(param);
@@ -477,9 +484,13 @@ INTERCEPTOR(void, _exit, int status) {
 #define COMMON_INTERCEPT_FUNCTION(name) INTERCEPT_FUNCTION(name)
 #include "sanitizer_common/sanitizer_signal_interceptors.inc"
 
+#endif  // SANITIZER_POSIX
+
 namespace __lsan {
 
 void InitializeInterceptors() {
+  // Fuchsia doesn't use interceptors that require any setup.
+#if !SANITIZER_FUCHSIA
   InitializeSignalInterceptors();
 
   INTERCEPT_FUNCTION(malloc);
@@ -515,6 +526,8 @@ void InitializeInterceptors() {
     Die();
   }
 #endif
+
+#endif  // !SANITIZER_FUCHSIA
 }
 
 } // namespace __lsan
diff --git a/libsanitizer/lsan/lsan_linux.cpp b/libsanitizer/lsan/lsan_linux.cpp
index 14a42b7..47c2f21 100644
--- a/libsanitizer/lsan/lsan_linux.cpp
+++ b/libsanitizer/lsan/lsan_linux.cpp
@@ -6,13 +6,13 @@
 //
 //===----------------------------------------------------------------------===//
 //
-// This file is a part of LeakSanitizer. Linux/NetBSD-specific code.
+// This file is a part of LeakSanitizer. Linux/NetBSD/Fuchsia-specific code.
 //
 //===----------------------------------------------------------------------===//
 
 #include "sanitizer_common/sanitizer_platform.h"
 
-#if SANITIZER_LINUX || SANITIZER_NETBSD
+#if SANITIZER_LINUX || SANITIZER_NETBSD || SANITIZER_FUCHSIA
 
 #include "lsan_allocator.h"
 
@@ -29,4 +29,4 @@ void ReplaceSystemMalloc() {}
 
 } // namespace __lsan
 
-#endif  // SANITIZER_LINUX || SANITIZER_NETBSD
+#endif  // SANITIZER_LINUX || SANITIZER_NETBSD || SANITIZER_FUCHSIA
diff --git a/libsanitizer/lsan/lsan_posix.cpp b/libsanitizer/lsan/lsan_posix.cpp
new file mode 100644
index 0000000..8e05915
--- /dev/null
+++ b/libsanitizer/lsan/lsan_posix.cpp
@@ -0,0 +1,96 @@
+//=-- lsan_posix.cpp -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This file is a part of LeakSanitizer.
+// Standalone LSan RTL code common to POSIX-like systems.
+//
+//===---------------------------------------------------------------------===//
+
+#include "sanitizer_common/sanitizer_platform.h"
+
+#if SANITIZER_POSIX
+#include "lsan.h"
+#include "lsan_allocator.h"
+#include "sanitizer_common/sanitizer_stacktrace.h"
+#include "sanitizer_common/sanitizer_tls_get_addr.h"
+
+namespace __lsan {
+
+ThreadContext::ThreadContext(int tid) : ThreadContextLsanBase(tid) {}
+
+struct OnStartedArgs {
+  uptr stack_begin;
+  uptr stack_end;
+  uptr cache_begin;
+  uptr cache_end;
+  uptr tls_begin;
+  uptr tls_end;
+  DTLS *dtls;
+};
+
+void ThreadContext::OnStarted(void *arg) {
+  auto args = reinterpret_cast<const OnStartedArgs *>(arg);
+  stack_begin_ = args->stack_begin;
+  stack_end_ = args->stack_end;
+  tls_begin_ = args->tls_begin;
+  tls_end_ = args->tls_end;
+  cache_begin_ = args->cache_begin;
+  cache_end_ = args->cache_end;
+  dtls_ = args->dtls;
+}
+
+void ThreadStart(u32 tid, tid_t os_id, ThreadType thread_type) {
+  OnStartedArgs args;
+  uptr stack_size = 0;
+  uptr tls_size = 0;
+  GetThreadStackAndTls(tid == 0, &args.stack_begin, &stack_size,
+                       &args.tls_begin, &tls_size);
+  args.stack_end = args.stack_begin + stack_size;
+  args.tls_end = args.tls_begin + tls_size;
+  GetAllocatorCacheRange(&args.cache_begin, &args.cache_end);
+  args.dtls = DTLS_Get();
+  ThreadContextLsanBase::ThreadStart(tid, os_id, thread_type, &args);
+}
+
+bool GetThreadRangesLocked(tid_t os_id, uptr *stack_begin, uptr *stack_end,
+                           uptr *tls_begin, uptr *tls_end, uptr *cache_begin,
+                           uptr *cache_end, DTLS **dtls) {
+  ThreadContext *context = static_cast<ThreadContext *>(
+      GetThreadRegistryLocked()->FindThreadContextByOsIDLocked(os_id));
+  if (!context)
+    return false;
+  *stack_begin = context->stack_begin();
+  *stack_end = context->stack_end();
+  *tls_begin = context->tls_begin();
+  *tls_end = context->tls_end();
+  *cache_begin = context->cache_begin();
+  *cache_end = context->cache_end();
+  *dtls = context->dtls();
+  return true;
+}
+
+void InitializeMainThread() {
+  u32 tid = ThreadCreate(0, 0, true);
+  CHECK_EQ(tid, 0);
+  ThreadStart(tid, GetTid());
+}
+
+static void OnStackUnwind(const SignalContext &sig, const void *,
+                          BufferedStackTrace *stack) {
+  stack->Unwind(StackTrace::GetNextInstructionPc(sig.pc), sig.bp, sig.context,
+                common_flags()->fast_unwind_on_fatal);
+}
+
+void LsanOnDeadlySignal(int signo, void *siginfo, void *context) {
+  HandleDeadlySignal(siginfo, context, GetCurrentThread(), &OnStackUnwind,
+                     nullptr);
+}
+
+}  // namespace __lsan
+
+#endif  // SANITIZER_POSIX
diff --git a/libsanitizer/lsan/lsan_posix.h b/libsanitizer/lsan/lsan_posix.h
new file mode 100644
index 0000000..840e427
--- /dev/null
+++ b/libsanitizer/lsan/lsan_posix.h
@@ -0,0 +1,49 @@
+//=-- lsan_posix.h -----------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===---------------------------------------------------------------------===//
+//
+// This file is a part of LeakSanitizer.
+// Standalone LSan RTL code common to POSIX-like systems.
+//
+//===---------------------------------------------------------------------===//
+
+#ifndef LSAN_POSIX_H
+#define LSAN_POSIX_H
+
+#include "lsan_thread.h"
+#include "sanitizer_common/sanitizer_platform.h"
+
+#if !SANITIZER_POSIX
+#error "lsan_posix.h is used only on POSIX-like systems (SANITIZER_POSIX)"
+#endif
+
+namespace __sanitizer {
+struct DTLS;
+}
+
+namespace __lsan {
+
+class ThreadContext : public ThreadContextLsanBase {
+ public:
+  explicit ThreadContext(int tid);
+  void OnStarted(void *arg) override;
+  uptr tls_begin() { return tls_begin_; }
+  uptr tls_end() { return tls_end_; }
+  DTLS *dtls() { return dtls_; }
+
+ private:
+  uptr tls_begin_ = 0;
+  uptr tls_end_ = 0;
+  DTLS *dtls_ = nullptr;
+};
+
+void ThreadStart(u32 tid, tid_t os_id,
+                 ThreadType thread_type = ThreadType::Regular);
+
+}  // namespace __lsan
+
+#endif  // LSAN_POSIX_H
diff --git a/libsanitizer/lsan/lsan_thread.cpp b/libsanitizer/lsan/lsan_thread.cpp
index 84e7ce6..40bdc25 100644
--- a/libsanitizer/lsan/lsan_thread.cpp
+++ b/libsanitizer/lsan/lsan_thread.cpp
@@ -13,12 +13,13 @@
 
 #include "lsan_thread.h"
 
+#include "lsan.h"
+#include "lsan_allocator.h"
+#include "lsan_common.h"
 #include "sanitizer_common/sanitizer_common.h"
 #include "sanitizer_common/sanitizer_placement_new.h"
 #include "sanitizer_common/sanitizer_thread_registry.h"
 #include "sanitizer_common/sanitizer_tls_get_addr.h"
-#include "lsan_allocator.h"
-#include "lsan_common.h"
 
 namespace __lsan {
 
@@ -26,7 +27,7 @@ static ThreadRegistry *thread_registry;
 
 static ThreadContextBase *CreateThreadContext(u32 tid) {
   void *mem = MmapOrDie(sizeof(ThreadContext), "ThreadContext");
-  return new(mem) ThreadContext(tid);
+  return new (mem) ThreadContext(tid);
 }
 
 static const uptr kMaxThreads = 1 << 13;
@@ -34,59 +35,26 @@ static const uptr kThreadQuarantineSize = 64;
 
 void InitializeThreadRegistry() {
   static ALIGNED(64) char thread_registry_placeholder[sizeof(ThreadRegistry)];
-  thread_registry = new(thread_registry_placeholder)
-    ThreadRegistry(CreateThreadContext, kMaxThreads, kThreadQuarantineSize);
+  thread_registry = new (thread_registry_placeholder)
+      ThreadRegistry(CreateThreadContext, kMaxThreads, kThreadQuarantineSize);
 }
 
-ThreadContext::ThreadContext(int tid)
-    : ThreadContextBase(tid),
-      stack_begin_(0),
-      stack_end_(0),
-      cache_begin_(0),
-      cache_end_(0),
-      tls_begin_(0),
-      tls_end_(0),
-      dtls_(nullptr) {}
-
-struct OnStartedArgs {
-  uptr stack_begin, stack_end,
-       cache_begin, cache_end,
-       tls_begin, tls_end;
-  DTLS *dtls;
-};
-
-void ThreadContext::OnStarted(void *arg) {
-  OnStartedArgs *args = reinterpret_cast<OnStartedArgs *>(arg);
-  stack_begin_ = args->stack_begin;
-  stack_end_ = args->stack_end;
-  tls_begin_ = args->tls_begin;
-  tls_end_ = args->tls_end;
-  cache_begin_ = args->cache_begin;
-  cache_end_ = args->cache_end;
-  dtls_ = args->dtls;
-}
+ThreadContextLsanBase::ThreadContextLsanBase(int tid)
+    : ThreadContextBase(tid) {}
 
-void ThreadContext::OnFinished() {
+void ThreadContextLsanBase::OnFinished() {
   AllocatorThreadFinish();
   DTLS_Destroy();
 }
 
-u32 ThreadCreate(u32 parent_tid, uptr user_id, bool detached) {
-  return thread_registry->CreateThread(user_id, detached, parent_tid,
-                                       /* arg */ nullptr);
+u32 ThreadCreate(u32 parent_tid, uptr user_id, bool detached, void *arg) {
+  return thread_registry->CreateThread(user_id, detached, parent_tid, arg);
 }
 
-void ThreadStart(u32 tid, tid_t os_id, ThreadType thread_type) {
-  OnStartedArgs args;
-  uptr stack_size = 0;
-  uptr tls_size = 0;
-  GetThreadStackAndTls(tid == 0, &args.stack_begin, &stack_size,
-                       &args.tls_begin, &tls_size);
-  args.stack_end = args.stack_begin + stack_size;
-  args.tls_end = args.tls_begin + tls_size;
-  GetAllocatorCacheRange(&args.cache_begin, &args.cache_end);
-  args.dtls = DTLS_Get();
-  thread_registry->StartThread(tid, os_id, thread_type, &args);
+void ThreadContextLsanBase::ThreadStart(u32 tid, tid_t os_id,
+                                        ThreadType thread_type, void *arg) {
+  thread_registry->StartThread(tid, os_id, thread_type, arg);
+  SetCurrentThread(tid);
 }
 
 void ThreadFinish() {
@@ -95,7 +63,8 @@ void ThreadFinish() {
 }
 
 ThreadContext *CurrentThreadContext() {
-  if (!thread_registry) return nullptr;
+  if (!thread_registry)
+    return nullptr;
   if (GetCurrentThread() == kInvalidTid)
     return nullptr;
   // No lock needed when getting current thread.
@@ -111,12 +80,12 @@ static bool FindThreadByUid(ThreadContextBase *tctx, void *arg) {
 }
 
 u32 ThreadTid(uptr uid) {
-  return thread_registry->FindThread(FindThreadByUid, (void*)uid);
+  return thread_registry->FindThread(FindThreadByUid, (void *)uid);
 }
 
 void ThreadJoin(u32 tid) {
   CHECK_NE(tid, kInvalidTid);
-  thread_registry->JoinThread(tid, /* arg */nullptr);
+  thread_registry->JoinThread(tid, /* arg */ nullptr);
 }
 
 void EnsureMainThreadIDIsCorrect() {
@@ -126,37 +95,16 @@ void EnsureMainThreadIDIsCorrect() {
 
 ///// Interface to the common LSan module. /////
 
-bool GetThreadRangesLocked(tid_t os_id, uptr *stack_begin, uptr *stack_end,
-                           uptr *tls_begin, uptr *tls_end, uptr *cache_begin,
-                           uptr *cache_end, DTLS **dtls) {
-  ThreadContext *context = static_cast<ThreadContext *>(
-      thread_registry->FindThreadContextByOsIDLocked(os_id));
-  if (!context) return false;
-  *stack_begin = context->stack_begin();
-  *stack_end = context->stack_end();
-  *tls_begin = context->tls_begin();
-  *tls_end = context->tls_end();
-  *cache_begin = context->cache_begin();
-  *cache_end = context->cache_end();
-  *dtls = context->dtls();
-  return true;
-}
-
 void ForEachExtraStackRange(tid_t os_id, RangeIteratorCallback callback,
-                            void *arg) {
-}
+                            void *arg) {}
 
-void LockThreadRegistry() {
-  thread_registry->Lock();
-}
+void LockThreadRegistry() { thread_registry->Lock(); }
 
-void UnlockThreadRegistry() {
-  thread_registry->Unlock();
-}
+void UnlockThreadRegistry() { thread_registry->Unlock(); }
 
 ThreadRegistry *GetThreadRegistryLocked() {
   thread_registry->CheckLocked();
   return thread_registry;
 }
 
-} // namespace __lsan
+}  // namespace __lsan
diff --git a/libsanitizer/lsan/lsan_thread.h b/libsanitizer/lsan/lsan_thread.h
index b869d06..0ab1582 100644
--- a/libsanitizer/lsan/lsan_thread.h
+++ b/libsanitizer/lsan/lsan_thread.h
@@ -16,38 +16,36 @@
 
 #include "sanitizer_common/sanitizer_thread_registry.h"
 
-namespace __sanitizer {
-struct DTLS;
-}
-
 namespace __lsan {
 
-class ThreadContext : public ThreadContextBase {
+class ThreadContextLsanBase : public ThreadContextBase {
  public:
-  explicit ThreadContext(int tid);
-  void OnStarted(void *arg) override;
+  explicit ThreadContextLsanBase(int tid);
   void OnFinished() override;
   uptr stack_begin() { return stack_begin_; }
   uptr stack_end() { return stack_end_; }
-  uptr tls_begin() { return tls_begin_; }
-  uptr tls_end() { return tls_end_; }
   uptr cache_begin() { return cache_begin_; }
   uptr cache_end() { return cache_end_; }
-  DTLS *dtls() { return dtls_; }
 
- private:
-  uptr stack_begin_, stack_end_,
-       cache_begin_, cache_end_,
-       tls_begin_, tls_end_;
-  DTLS *dtls_;
+  // The argument is passed on to the subclass's OnStarted member function.
+  static void ThreadStart(u32 tid, tid_t os_id, ThreadType thread_type,
+                          void *onstarted_arg);
+
+ protected:
+  uptr stack_begin_ = 0;
+  uptr stack_end_ = 0;
+  uptr cache_begin_ = 0;
+  uptr cache_end_ = 0;
 };
 
+// This subclass of ThreadContextLsanBase is declared in an OS-specific header.
+class ThreadContext;
+
 void InitializeThreadRegistry();
+void InitializeMainThread();
 
-void ThreadStart(u32 tid, tid_t os_id,
-                 ThreadType thread_type = ThreadType::Regular);
+u32 ThreadCreate(u32 tid, uptr uid, bool detached, void *arg = nullptr);
 void ThreadFinish();
-u32 ThreadCreate(u32 tid, uptr uid, bool detached);
 void ThreadJoin(u32 tid);
 u32 ThreadTid(uptr uid);
 
@@ -55,6 +53,7 @@ u32 GetCurrentThread();
 void SetCurrentThread(u32 tid);
 ThreadContext *CurrentThreadContext();
 void EnsureMainThreadIDIsCorrect();
+
 }  // namespace __lsan
 
 #endif  // LSAN_THREAD_H