Read proc/self/maps to find main thread stack base

pthread_getattr_np implementation in bionic throws sigabrt on failure to
read proc/ file. Implement this function to avoid crashes.

BUG=1129941

Change-Id: I54b94a609201a998924aaa8c8e77051f85acf377
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2425744
Commit-Queue: ssid <ssid@chromium.org>
Reviewed-by: Mike Wittman <wittman@chromium.org>
Reviewed-by: Tommy Nyquist <nyquist@chromium.org>
Cr-Commit-Position: refs/heads/master@{#810829}

base/BUILD.gn

@@ -3096,6 +3096,7 @@ test("base_unittests") {
       sources += [
         "cpu_affinity_posix_unittest.cc",
         "profiler/stack_copier_signal_unittest.cc",
+        "profiler/thread_delegate_posix_unittest.cc",
       ]
     }
   }

base/profiler/native_unwinder_android_unittest.cc

@@ -73,8 +73,11 @@ std::vector<Frame> CaptureScenario(
       scenario,
       BindLambdaForTesting(
           [&](SamplingProfilerThreadToken target_thread_token) {
-            auto stack_copier = std::make_unique<StackCopierSignal>(
-                std::make_unique<ThreadDelegatePosix>(target_thread_token));
+            auto thread_delegate =
+                ThreadDelegatePosix::Create(target_thread_token);
+            ASSERT_TRUE(thread_delegate);
+            auto stack_copier =
+                std::make_unique<StackCopierSignal>(std::move(thread_delegate));
             std::unique_ptr<StackBuffer> stack_buffer =
                 StackSampler::CreateStackBuffer();
 

base/profiler/stack_copier_signal_unittest.cc

@@ -95,8 +95,10 @@ TEST(StackCopierSignalTest, MAYBE_CopyStack) {
   RegisterContext context;
   TestStackCopierDelegate stack_copier_delegate;
 
-  StackCopierSignal copier(std::make_unique<ThreadDelegatePosix>(
-      GetSamplingProfilerCurrentThreadToken()));
+  auto thread_delegate =
+      ThreadDelegatePosix::Create(GetSamplingProfilerCurrentThreadToken());
+  ASSERT_TRUE(thread_delegate);
+  StackCopierSignal copier(std::move(thread_delegate));
 
   // Copy the sentinel values onto the stack. Volatile to defeat compiler
   // optimizations.
@@ -132,8 +134,10 @@ TEST(StackCopierSignalTest, MAYBE_CopyStackTimestamp) {
   RegisterContext context;
   TestStackCopierDelegate stack_copier_delegate;
 
-  StackCopierSignal copier(std::make_unique<ThreadDelegatePosix>(
-      GetSamplingProfilerCurrentThreadToken()));
+  auto thread_delegate =
+      ThreadDelegatePosix::Create(GetSamplingProfilerCurrentThreadToken());
+  ASSERT_TRUE(thread_delegate);
+  StackCopierSignal copier(std::move(thread_delegate));
 
   TimeTicks before = TimeTicks::Now();
   bool result = copier.CopyStack(&stack_buffer, &stack_top, &timestamp,
@@ -159,8 +163,10 @@ TEST(StackCopierSignalTest, MAYBE_CopyStackDelegateInvoked) {
   RegisterContext context;
   TestStackCopierDelegate stack_copier_delegate;
 
-  StackCopierSignal copier(std::make_unique<ThreadDelegatePosix>(
-      GetSamplingProfilerCurrentThreadToken()));
+  auto thread_delegate =
+      ThreadDelegatePosix::Create(GetSamplingProfilerCurrentThreadToken());
+  ASSERT_TRUE(thread_delegate);
+  StackCopierSignal copier(std::move(thread_delegate));
 
   bool result = copier.CopyStack(&stack_buffer, &stack_top, &timestamp,
                                  &context, &stack_copier_delegate);
@@ -190,7 +196,9 @@ TEST(StackCopierSignalTest, MAYBE_CopyStackFromOtherThread) {
   const SamplingProfilerThreadToken thread_token =
       target_thread.GetThreadToken();
 
-  StackCopierSignal copier(std::make_unique<ThreadDelegatePosix>(thread_token));
+  auto thread_delegate = ThreadDelegatePosix::Create(thread_token);
+  ASSERT_TRUE(thread_delegate);
+  StackCopierSignal copier(std::move(thread_delegate));
 
   bool result = copier.CopyStack(&stack_buffer, &stack_top, &timestamp,
                                  &context, &stack_copier_delegate);

base/profiler/stack_sampler_android.cc

@@ -21,9 +21,11 @@ std::unique_ptr<StackSampler> StackSampler::Create(
     UnwindersFactory core_unwinders_factory,
     RepeatingClosure record_sample_callback,
     StackSamplerTestDelegate* test_delegate) {
+  auto thread_delegate = ThreadDelegatePosix::Create(thread_token);
+  if (!thread_delegate)
+    return nullptr;
   return std::make_unique<StackSamplerImpl>(
-      std::make_unique<StackCopierSignal>(
-          std::make_unique<ThreadDelegatePosix>(thread_token)),
+      std::make_unique<StackCopierSignal>(std::move(thread_delegate)),
       std::move(core_unwinders_factory), module_cache,
       std::move(record_sample_callback), test_delegate);
 }

base/profiler/thread_delegate_posix.cc

@@ -2,18 +2,44 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include <inttypes.h>
 #include <pthread.h>
+#include <stdio.h>
 
+#include "base/memory/ptr_util.h"
+#include "base/optional.h"
 #include "base/process/process_handle.h"
 #include "base/profiler/thread_delegate_posix.h"
 #include "base/stl_util.h"
-
 #include "build/build_config.h"
 
+#if defined(OS_ANDROID)
+#include "base/files/file_util.h"
+#include "base/files/scoped_file.h"
+#endif
+
 namespace base {
 
 namespace {
 
+#if defined(OS_ANDROID)
+base::Optional<uintptr_t> GetAndroidMainThreadStackBaseAddressImpl() {
+  char line[1024];
+  base::ScopedFILE fp(base::OpenFile(base::FilePath("/proc/self/maps"), "r"));
+  uintptr_t stack_addr = reinterpret_cast<uintptr_t>(line);
+  if (!fp)
+    return base::nullopt;
+  while (fgets(line, sizeof(line), fp.get()) != nullptr) {
+    uintptr_t start, end;
+    if (sscanf(line, "%" SCNxPTR "-%" SCNxPTR, &start, &end) == 2) {
+      if (start <= stack_addr && stack_addr < end)
+        return end;
+    }
+  }
+  return base::nullopt;
+}
+#endif
+
 uintptr_t GetThreadStackBaseAddressImpl(
     SamplingProfilerThreadToken thread_token) {
   pthread_attr_t attr;
@@ -27,15 +53,18 @@ uintptr_t GetThreadStackBaseAddressImpl(
   return base_address;
 }
 
-uintptr_t GetThreadStackBaseAddress(SamplingProfilerThreadToken thread_token) {
+base::Optional<uintptr_t> GetThreadStackBaseAddress(
+    SamplingProfilerThreadToken thread_token) {
 #if defined(OS_ANDROID)
-  // Caches the main thread base address on Android since Bionic has to read
-  // /proc/$PID/maps to obtain it. Other thread base addresses are sourced from
-  // pthread state so are cheap to get.
+  // The implementation of pthread_getattr_np() in Bionic reads proc/self/maps
+  // to find the main thread base address, and throws SIGABRT when it fails to
+  // read or parse the file. So, try to read the maps to get the main thread
+  // stack base and cache the result. Other thread base addresses are sourced
+  // from pthread state so are cheap to get.
   const bool is_main_thread = thread_token.id == GetCurrentProcId();
   if (is_main_thread) {
-    static const uintptr_t main_thread_base_address =
-        GetThreadStackBaseAddressImpl(thread_token);
+    static const base::Optional<uintptr_t> main_thread_base_address =
+        GetAndroidMainThreadStackBaseAddressImpl();
     return main_thread_base_address;
   }
 #endif
@@ -44,10 +73,18 @@ uintptr_t GetThreadStackBaseAddress(SamplingProfilerThreadToken thread_token) {
 
 }  // namespace
 
-ThreadDelegatePosix::ThreadDelegatePosix(
-    SamplingProfilerThreadToken thread_token)
-    : thread_id_(thread_token.id),
-      thread_stack_base_address_(GetThreadStackBaseAddress(thread_token)) {}
+// static
+std::unique_ptr<ThreadDelegatePosix> ThreadDelegatePosix::Create(
+    SamplingProfilerThreadToken thread_token) {
+  base::Optional<uintptr_t> base_address =
+      GetThreadStackBaseAddress(thread_token);
+  if (!base_address)
+    return nullptr;
+  return base::WrapUnique(
+      new ThreadDelegatePosix(thread_token.id, *base_address));
+}
+
+ThreadDelegatePosix::~ThreadDelegatePosix() = default;
 
 PlatformThreadId ThreadDelegatePosix::GetThreadId() const {
   return thread_id_;
@@ -117,4 +154,8 @@ std::vector<uintptr_t*> ThreadDelegatePosix::GetRegistersToRewrite(
 #endif
 }
 
+ThreadDelegatePosix::ThreadDelegatePosix(PlatformThreadId id,
+                                         uintptr_t base_address)
+    : thread_id_(id), thread_stack_base_address_(base_address) {}
+
 }  // namespace base

base/profiler/thread_delegate_posix.h

@@ -16,7 +16,10 @@ namespace base {
 // POSIX.
 class BASE_EXPORT ThreadDelegatePosix : public ThreadDelegate {
  public:
-  ThreadDelegatePosix(SamplingProfilerThreadToken thread_token);
+  static std::unique_ptr<ThreadDelegatePosix> Create(
+      SamplingProfilerThreadToken thread_token);
+
+  ~ThreadDelegatePosix() override;
 
   ThreadDelegatePosix(const ThreadDelegatePosix&) = delete;
   ThreadDelegatePosix& operator=(const ThreadDelegatePosix&) = delete;
@@ -28,6 +31,8 @@ class BASE_EXPORT ThreadDelegatePosix : public ThreadDelegate {
       RegisterContext* thread_context) override;
 
  private:
+  ThreadDelegatePosix(PlatformThreadId id, uintptr_t base_address);
+
   const PlatformThreadId thread_id_;
   const uintptr_t thread_stack_base_address_;
 };

base/profiler/thread_delegate_posix_unittest.cc

@@ -0,0 +1,42 @@
+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/profiler/thread_delegate_posix.h"
+
+#include "base/process/process_handle.h"
+#include "build/build_config.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace base {
+
+// ASAN moves local variables outside of the stack extents.
+#if defined(ADDRESS_SANITIZER)
+#define MAYBE_CurrentThreadBase DISABLED_CurrentThreadBase
+#else
+#define MAYBE_CurrentThreadBase CurrentThreadBase
+#endif
+TEST(ThreadDelegatePosixTest, MAYBE_CurrentThreadBase) {
+  auto delegate =
+      ThreadDelegatePosix::Create(GetSamplingProfilerCurrentThreadToken());
+  ASSERT_TRUE(delegate);
+  uintptr_t base = delegate->GetStackBaseAddress();
+  EXPECT_GT(base, 0u);
+  uintptr_t stack_addr = reinterpret_cast<uintptr_t>(&base);
+  // Check that end of stack is within 4MiB of a current stack address.
+  EXPECT_LE(base, stack_addr + 4 * 1024 * 1024);
+}
+
+#if defined(OS_ANDROID)
+
+TEST(ThreadDelegatePosixTest, AndroidMainThreadStackBase) {
+  // The delegate does not use pthread id for main thread.
+  auto delegate = ThreadDelegatePosix::Create(
+      SamplingProfilerThreadToken{GetCurrentProcId(), pthread_t()});
+  ASSERT_TRUE(delegate);
+  uintptr_t base = delegate->GetStackBaseAddress();
+  EXPECT_GT(base, 0u);
+}
+
+#endif  // defined(OS_ANDROID)
+}  // namespace base