[perf-prof] Fix erroneous code offsets in unwinding info

src/perf-jit.cc

 // Copyright 2016 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 200 matching lines @@
   Code* code = abstract_code->GetCode();
   DCHECK(code->instruction_start() == code->address() + Code::kHeaderSize);
 
   // Debug info has to be emitted first.
   if (FLAG_perf_prof && shared != nullptr) {
     LogWriteDebugInfo(code, shared);
   }
 
   const char* code_name = name;
   uint8_t* code_pointer = reinterpret_cast<uint8_t*>(code->instruction_start());
+  // Code generated by Crankshaft or Turbofan will have the safepoint table
+  // directly after instructions. There is no need to record the safepoint table
+  // itself.
   uint32_t code_size = code->is_crankshafted() ? code->safepoint_table_offset()
                                                : code->instruction_size();
 
   // Unwinding info comes right after debug info.
   if (FLAG_perf_prof_unwinding_info) LogWriteUnwindingInfo(code);
 
   static const char string_terminator[] = "\0";
 
   PerfJitCodeLoad code_load;
   code_load.event_ = PerfJitCodeLoad::kLoad;
@@ skipping 167 matching lines @@
   header.time_stamp_ =
       static_cast<uint64_t>(base::OS::TimeCurrentMillis() * 1000.0);
   header.flags_ = 0;
 
   LogWriteBytes(reinterpret_cast<const char*>(&header), sizeof(header));
 }
 
 #endif  // V8_OS_LINUX
 }  // namespace internal
 }  // namespace v8