Cleaner fall-back stack capture for --enable-heap-profiling=native.

base/trace_event/heap_profiler_allocation_context_tracker.cc

 // Copyright 2015 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/trace_event/heap_profiler_allocation_context_tracker.h"
 
 #include <algorithm>
 #include <iterator>
 
 #include "base/atomicops.h"
@@ skipping 185 matching lines @@
               StackFrame::FromTraceEventName(stack_frame.trace_event_name);
         }
         break;
       }
     case CaptureMode::NATIVE_STACK:
       {
         // 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[128];
-        static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
-                      "not requesting enough frames to fill Backtrace");
-#if HAVE_TRACE_STACK_FRAME_POINTERS && !defined(OS_NACL)
-        size_t frame_count = debug::TraceStackFramePointers(
-            frames,
-            arraysize(frames),
-            1 /* exclude this function from the trace */ );
-#else
-        size_t frame_count = 0;
-        NOTREACHED();
-#endif
+#if !defined(OS_NACL)  // We don't build base/debug/stack_trace.cc for NaCl.
+#if HAVE_TRACE_STACK_FRAME_POINTERS
+      const void* frames[128];
+      static_assert(arraysize(frames) >= Backtrace::kMaxFrameCount,
+                    "not requesting enough frames to fill Backtrace");
+      size_t frame_count = debug::TraceStackFramePointers(
+          frames, arraysize(frames),
+          1 /* exclude this function from the trace */);
+#else   // HAVE_TRACE_STACK_FRAME_POINTERS
+      // Fall-back to capturing the stack with base::debug::StackTrace,
+      // which is likely slower, but more reliable.
+      base::debug::StackTrace stack_trace(Backtrace::kMaxFrameCount);
+      size_t frame_count = 0u;
+      const void* const* frames = stack_trace.Addresses(&frame_count);

[dcheng, 2017/03/28 06:16:23]

Nit: this will capture the constructor for StackTrace and this function as well?
Is it worth trimming to match the HAVE_STACK_FRAME_POINTERS path?

(Also, the CL description says that HAVE_STACK_FRAME_POINTERS is now a
function-style macro, but it's not invoked with () here?)

[Wez, 2017/03/28 06:38:21]

That is a fair point; it doesn't affect the functionality per-se but reducing
the number of pointless frames to symbolize SGTM. :)

I think this call-site should trim a single frame, and StackTrace should
probably itself be fixed to trim the right number of frames - I think that's
tricky to determine, though, in optimized builds.
CL used to do that but dskiba@ preferred to stay consistent with the other HAVE_
macros, so reverted that change - have fixed description.

+#endif  // HAVE_TRACE_STACK_FRAME_POINTERS
 
-        // Copy frames backwards
-        size_t backtrace_capacity = backtrace_end - backtrace;
-        int32_t top_frame_index = (backtrace_capacity >= frame_count)
-                                      ? 0
-                                      : frame_count - backtrace_capacity;
-        for (int32_t i = frame_count - 1; i >= top_frame_index; --i) {
-          const void* frame = frames[i];
-          *backtrace++ = StackFrame::FromProgramCounter(frame);
-        }
-        break;
+      // Copy frames backwards
+      size_t backtrace_capacity = backtrace_end - backtrace;
+      int32_t top_frame_index = (backtrace_capacity >= frame_count)
+                                    ? 0
+                                    : frame_count - backtrace_capacity;
+      for (int32_t i = frame_count - 1; i >= top_frame_index; --i) {
+        const void* frame = frames[i];
+        *backtrace++ = StackFrame::FromProgramCounter(frame);
       }
+#endif  // !defined(OS_NACL)
+      break;
+    }
   }
 
   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.
   if (!task_contexts_.empty()) {
     ctx->type_name = task_contexts_.back();
   } else if (!pseudo_stack_.empty()) {
     // If task context was unavailable, then the category names are taken from
     // trace events.
     ctx->type_name = pseudo_stack_.back().trace_event_category;
   } else {
     ctx->type_name = nullptr;
   }
 
   return true;
 }
 
 }  // namespace trace_event
 }  // namespace base