Record async "task backtraces"

base/debug/task_annotator.cc

 // Copyright 2014 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/debug/task_annotator.h"
 
 #include "base/debug/alias.h"
 #include "base/pending_task.h"
 #include "base/trace_event/trace_event.h"
 #include "base/tracked_objects.h"
@@ skipping 34 matching lines @@
   // runner.
   TRACE_EVENT_WITH_MEMORY_TAG2(
       "toplevel",
       run_function,
       pending_task.posted_from.function_name(),  // Name for memory tracking.
       "src_file",
       pending_task.posted_from.file_name(),
       "src_func",
       pending_task.posted_from.function_name());
 
-  // Before running the task, store the program counter where it was posted
-  // and deliberately alias it to ensure it is on the stack if the task
-  // crashes. Be careful not to assume that the variable itself will have the
-  // expected value when displayed by the optimizer in an optimized build.
-  // Look at a memory dump of the stack.
-  const void* program_counter = pending_task.posted_from.program_counter();
-  debug::Alias(&program_counter);
+  // Before running the task, store the task backtrace with the chain of
+  // PostTasks that resulted in this call and deliberately alias it to ensure
+  // it is on the stack if the task crashes. Be careful not to assume that the
+  // variable itself will have the expected value when displayed by the
+  // optimizer in an optimized build. Look at a memory dump of the stack.
+  const void* task_backtrace[4];
+  memcpy(&task_backtrace[0], &pending_task.task_backtrace[0],
+         sizeof(task_backtrace));
+  debug::Alias(&task_backtrace);
 
   pending_task.task.Run();
 
   stopwatch.Stop();
   tracked_objects::ThreadData::TallyRunOnNamedThreadIfTracking(
       pending_task, stopwatch);
 }
 
 uint64 TaskAnnotator::GetTaskTraceID(const PendingTask& task) const {
   return (static_cast<uint64>(task.sequence_num) << 32) |
          ((static_cast<uint64>(reinterpret_cast<intptr_t>(this)) << 32) >> 32);
 }
 
 }  // namespace debug
 }  // namespace base