[tracing] Add native allocation tracing mode.

base/trace_event/heap_profiler_allocation_context_tracker.cc

Index: base/trace_event/heap_profiler_allocation_context_tracker.cc
diff --git a/base/trace_event/heap_profiler_allocation_context_tracker.cc b/base/trace_event/heap_profiler_allocation_context_tracker.cc
index e192bc833fd950507a5756387b84b5fc92e827ed..7a75513d7659338b751093a9ac1b3db127a405ec 100644
--- a/base/trace_event/heap_profiler_allocation_context_tracker.cc
+++ b/base/trace_event/heap_profiler_allocation_context_tracker.cc
@@ -14,7 +14,8 @@
 namespace base {
 namespace trace_event {
 
-subtle::Atomic32 AllocationContextTracker::capture_enabled_ = 0;
+subtle::Atomic32 AllocationContextTracker::capture_mode_ =
+    static_cast<int32_t>(AllocationContextTracker::CaptureMode::DISABLED);
 
 namespace {
 
@@ -60,21 +61,21 @@ AllocationContextTracker::~AllocationContextTracker() {}
 
 // static
 void AllocationContextTracker::SetCurrentThreadName(const char* name) {
-  if (name && capture_enabled()) {
+  if (name && capture_mode() != CaptureMode::DISABLED) {
     GetInstanceForCurrentThread()->thread_name_ = name;
   }
 }
 
 // static
-void AllocationContextTracker::SetCaptureEnabled(bool enabled) {
+void AllocationContextTracker::SetCaptureMode(CaptureMode mode) {
   // When enabling capturing, also initialize the TLS slot. This does not create
   // a TLS instance yet.
-  if (enabled && !g_tls_alloc_ctx_tracker.initialized())
+  if (mode != CaptureMode::DISABLED && !g_tls_alloc_ctx_tracker.initialized())
     g_tls_alloc_ctx_tracker.Initialize(DestructAllocationContextTracker);
 
-  // Release ordering ensures that when a thread observes |capture_enabled_| to
+  // Release ordering ensures that when a thread observes |capture_mode_| to
   // be true through an acquire load, the TLS slot has been initialized.
-  subtle::Release_Store(&capture_enabled_, enabled);
+  subtle::Release_Store(&capture_mode_, static_cast<int32_t>(mode));
 }
 
 void AllocationContextTracker::PushPseudoStackFrame(
@@ -129,26 +130,66 @@ AllocationContext AllocationContextTracker::GetContextSnapshot() {
     return ctx;
   }
 
-  // Fill the backtrace.
-  {
-    auto backtrace = std::begin(ctx.backtrace.frames);
-    auto backtrace_end = std::end(ctx.backtrace.frames);
+  CaptureMode mode = static_cast<CaptureMode>(
+      subtle::NoBarrier_Load(&capture_mode_));
 
-    // Add the thread name as the first entry
-    if (thread_name_) {
-      *backtrace++ = StackFrame::FromThreadName(thread_name_);
-    }
+  auto backtrace = std::begin(ctx.backtrace.frames);
+  auto backtrace_end = std::end(ctx.backtrace.frames);
 
-    for (const char* event_name: pseudo_stack_) {
-      if (backtrace == backtrace_end) {
+  // Add the thread name as the first entry
+  if (thread_name_) {
+    *backtrace++ = StackFrame::FromThreadName(thread_name_);
+  }
+
+  switch (mode) {
+    case CaptureMode::DISABLED:
+      {
         break;
       }
-      *backtrace++ = StackFrame::FromTraceEventName(event_name);
-    }
-
-    ctx.backtrace.frame_count = backtrace - std::begin(ctx.backtrace.frames);
+    case CaptureMode::PSEUDO_STACK:
+      {
+        for (const auto& event_name: pseudo_stack_) {
+          if (backtrace == backtrace_end) {
+            break;
+          }
+          *backtrace++ = StackFrame::FromTraceEventName(event_name);
+        }
+        break;
+      }
+#if ENABLE_NATIVE_ALLOCATION_TRACES
+    case CaptureMode::NATIVE_STACK:
+      {
+        // base::trace_event::AllocationContextTracker::GetContextSnapshot()
+        const size_t kKnownFrameCount = 1;
+
+        // Backtrace contract requires us to return bottom frames, i.e.
+        // from main() and up. Stack unwinding produces top frames, i.e.
+        // from this point and up until main(). We request many frames to
+        // make sure we reach main(), and then copy bottom portion of them.
+        const void* frames[50];
+        static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
+                      "not requesting enough frames to fill Backtrace");
+        size_t frame_count = debug::TraceStackFramePointers(
+            frames,
+            arraysize(frames),
+            kKnownFrameCount);
+
+        // Copy frames backwards
+        size_t backtrace_capacity = backtrace_end - backtrace;
+        ssize_t top_frame_index = (backtrace_capacity >= frame_count) ?
+            0 :
+            frame_count - backtrace_capacity;
+        for (ssize_t i = frame_count - 1; i >= top_frame_index; --i) {
+          const void* frame = frames[i];
+          *backtrace++ = StackFrame::FromProgramCounter(frame);
+        }
+        break;
+      }
+#endif  // ENABLE_NATIVE_ALLOCATION_TRACES
   }
 
+  ctx.backtrace.frame_count = backtrace - std::begin(ctx.backtrace.frames);
+
   // TODO(ssid): Fix crbug.com/594803 to add file name as 3rd dimension
   // (component name) in the heap profiler and not piggy back on the type name.
   ctx.type_name = task_contexts_.empty() ? nullptr : task_contexts_.back();