CPU profiler: increase the max number of captured frames.

src/sampler.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_SAMPLER_H_
 #define V8_SAMPLER_H_
 
 #include "src/base/atomicops.h"
 #include "src/frames.h"
 #include "src/globals.h"
@@ skipping 26 matching lines @@
         frames_count(0),
         has_external_callback(false),
         top_frame_type(StackFrame::NONE) {}
   void Init(Isolate* isolate, const RegisterState& state);
   StateTag state;  // The state of the VM.
   Address pc;      // Instruction pointer.
   union {
     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;
 };
 
 class Sampler {
  public:
   // Initializes the Sampler support. Called once at VM startup.
   static void SetUp();
   static void TearDown();
 
@@ skipping 58 matching lines @@
   bool is_counting_samples_;
   // Counts stack samples taken in JS VM state.
   unsigned js_and_external_sample_count_;
   DISALLOW_IMPLICIT_CONSTRUCTORS(Sampler);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_SAMPLER_H_