Attempt at enabling profiler

runtime/vm/profiler.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include <cstdio>
 
 #include "platform/utils.h"
 
 #include "vm/isolate.h"
 #include "vm/json_stream.h"
 #include "vm/native_symbol.h"
 #include "vm/object.h"
 #include "vm/os.h"
 #include "vm/profiler.h"
 
 namespace dart {
 
 // Notes on locking and signal handling:
-
+//
 // The ProfilerManager has a single monitor (monitor_). This monitor guards
 // access to the schedule list of isolates (isolates_, isolates_size_, etc).
 //
 // Each isolate has a mutex (profiler_data_mutex_) which protects access
 // to the isolate's profiler data.
 //
 // Locks can be taken in this order:
 //   1. ProfilerManager::monitor_
 //   2. isolate->profiler_data_mutex_
 // In other words, it is not acceptable to take ProfilerManager::monitor_
@@ skipping 20 matching lines @@
 // is sent the SIGPROF, it is removed from the scheduled isolate list.
 // Inside the signal handler, after the sample is taken, the isolate is
 // added to the scheduled isolate list again. The side effect of this is
 // that the signal handler must be able to acquire the isolate profiler data
 // mutex and the profile manager monitor. When an isolate running thread
 // (potential signal target) calls into an entry point which acquires
 // ProfileManager::monitor_ signal delivery must be blocked. An example is
 // Isolate::SetCurrent which blocks signal delivery while removing the old
 // current isolate from the scheduled list and adding the new current isolate
 // to the scheduled list.
+//
+
+// Notes on stack frame walking:
+//
+// The sampling profiler will collect up to Sample::kNumStackFrames stack frames
+// The stack frame walking code uses the frame pointer to traverse the stack.
+// If the VM is compiled without frame pointers (which is the default on
+// recent GCC versions with optimizing enabled) the stack walking code will
+// fail (sometimes leading to a crash).
+//
 
 
-DEFINE_FLAG(bool, profile, false, "Enable Sampling Profiler");
+DEFINE_FLAG(bool, profile, true, "Enable Sampling Profiler");
 
 bool ProfilerManager::initialized_ = false;
 bool ProfilerManager::shutdown_ = false;
 Monitor* ProfilerManager::monitor_ = NULL;
 Isolate** ProfilerManager::isolates_ = NULL;
 intptr_t ProfilerManager::isolates_capacity_ = 0;
 intptr_t ProfilerManager::isolates_size_ = 0;
 
 
 void ProfilerManager::InitOnce() {
@@ skipping 490 matching lines @@
     return false;
   }
   uintptr_t cursor = reinterpret_cast<uintptr_t>(fp);
   cursor += sizeof(fp);
   bool r = cursor >= stack_lower_ && cursor <= stack_upper_;
   return r;
 }
 
 
 }  // namespace dart