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

The unwinding information we emit wrongly encodes code locations as relative
offsets. If we look at the .eh_frame section of shared object generated by "perf
inject" using "objdump -g":

~~~
00000000 0000000000000018 00000000 CIE
(snip)
0000001c 0000000000000028 00000020 FDE cie=00000000 pc=fffffffffffffee8..00000000000017f8
(snip)
00000048 ZERO terminator
~~~

We can see the range that the FDE entry covers is incorrect, it should point to
where the .text section is, at address 0x40 on a 64-bit architecture.

The reason for this was that the PerfJitLogger logs a code size that is
different from the one we've used when encoding the unwinding information. The
logger will ignore the safepoint table while the unwinding info assumes it is
part of the code.

BUG=

Review-Url: https://codereview.chromium.org/2790403002
Cr-Commit-Position: refs/heads/master@{#44378}

src/compiler/code-generator.cc

@@ -220,10 +220,13 @@ Handle<Code> CodeGenerator::GenerateCode() {
     }
   }
 
-  safepoints()->Emit(masm(), frame()->GetTotalFrameSlotCount());
-
+  // The PerfJitLogger logs code up until here, excluding the safepoint
+  // table. Resolve the unwinding info now so it is aware of the same code size
+  // as reported by perf.
   unwinding_info_writer_.Finish(masm()->pc_offset());
 
+  safepoints()->Emit(masm(), frame()->GetTotalFrameSlotCount());
+
   Handle<Code> result = v8::internal::CodeGenerator::MakeCodeEpilogue(
       masm(), unwinding_info_writer_.eh_frame_writer(), info, Handle<Object>());
   result->set_is_turbofanned(true);

src/perf-jit.cc

@@ -218,6 +218,9 @@ void PerfJitLogger::LogRecordedBuffer(AbstractCode* abstract_code,
 
   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();