A64: Skip samples that have sp = 0 in CPU profiler.

src/sampler.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 322 matching lines @@
 
   Sampler* sampler = isolate->logger()->sampler();
   if (sampler == NULL || !sampler->IsActive()) return;
 
   SampleHelper helper;
   TickSample* sample = helper.Init(sampler, isolate);
   if (sample == NULL) return;
 
 #if defined(USE_SIMULATOR)
   helper.FillRegisters(sample);
+  // It possible that the simulator is interrupted while it is updating
+  // the sp register. A64 simulator does this in two steps:
+  // first setting it to zero and then setting it to the new value.
+  // Bailout if sp doesn't contain the new value.
+  if (sample->sp == 0) return;
 #else
   // Extracting the sample from the context is extremely machine dependent.
   ucontext_t* ucontext = reinterpret_cast<ucontext_t*>(context);
   mcontext_t& mcontext = ucontext->uc_mcontext;
   sample->state = isolate->current_vm_state();
 #if defined(__linux__) || defined(__ANDROID__)
 #if V8_HOST_ARCH_IA32
   sample->pc = reinterpret_cast<Address>(mcontext.gregs[REG_EIP]);
   sample->sp = reinterpret_cast<Address>(mcontext.gregs[REG_ESP]);
   sample->fp = reinterpret_cast<Address>(mcontext.gregs[REG_EBP]);
@@ skipping 345 matching lines @@
   SamplerThread::RemoveActiveSampler(this);
   SetActive(false);
 }
 
 void Sampler::SampleStack(TickSample* sample) {
   sample->Trace(isolate_);
   if (++samples_taken_ < 0) samples_taken_ = 0;
 }
 
 } }  // namespace v8::internal