CPU profiler: increase the max number of captured frames.

src/sampler.h

Index: src/sampler.h
diff --git a/src/sampler.h b/src/sampler.h
index fe94a02e9350d1437d5ac63fc22a03f8989f6758..80fe5a978a83018d06951407c02a20116bef1c32 100644
--- a/src/sampler.h
+++ b/src/sampler.h
@@ -44,10 +44,11 @@ struct TickSample {
     Address tos;   // Top stack value (*sp).
     Address external_callback;
   };
-  static const int kMaxFramesCount = 64;
+  static const unsigned kMaxFramesCountLog2 = 8;
+  static const unsigned kMaxFramesCount = (1 << kMaxFramesCountLog2) - 1;

[loislo, 2014/06/24 13:09:21]

why do you have -1 here?

[alph, 2014/06/24 13:21:54]

the max value that can be stored in frames_count is 255 which is 2^8-1

   Address stack[kMaxFramesCount];  // Call stack.
   TimeTicks timestamp;
-  int frames_count : 8;  // Number of captured frames.
+  unsigned frames_count : kMaxFramesCountLog2;  // Number of captured frames.

[Jakob Kummerow, 2014/06/24 13:54:37]

I'm not sure this will work. IIRC we've had an issue before where MSVS insisted
on sign-extending a packed value when reading it back out, but I'm not sure if
the circumstances were identical. If this fails on Windows (can you test locally
before landing?), this would be something to take a closer look at.

[alph, 2014/06/24 14:10:23]

MSVC is noisy about implicit signed/unsigned conversions. But I seem to have all
of them fixed. I've run the try jobs.

Alternatively, I can add an extra bit here and keep it signed int if you like.

   bool has_external_callback : 1;
   StackFrame::Type top_frame_type : 4;
 };