Reland Implement .eh_frame writer and disassembler.

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 303 matching lines @@
     entry.line_number_ = line_number;
     entry.column_ = column_offset;
     LogWriteBytes(reinterpret_cast<const char*>(&entry), sizeof(entry));
     LogWriteBytes(name_string.get(), name_length + 1);
   }
   char padding_bytes[] = "\0\0\0\0\0\0\0\0";
   LogWriteBytes(padding_bytes, padding);
 }
 
 void PerfJitLogger::LogWriteUnwindingInfo(Code* code) {
-  EhFrameHdr eh_frame_hdr(code);
-
   PerfJitCodeUnwindingInfo unwinding_info_header;
   unwinding_info_header.event_ = PerfJitCodeLoad::kUnwindingInfo;
   unwinding_info_header.time_stamp_ = GetTimestamp();
   unwinding_info_header.eh_frame_hdr_size_ = EhFrameHdr::kRecordSize;
 
   if (code->has_unwinding_info()) {
     unwinding_info_header.unwinding_size_ = code->unwinding_info_size();
     unwinding_info_header.mapped_size_ = unwinding_info_header.unwinding_size_;
   } else {
     unwinding_info_header.unwinding_size_ = EhFrameHdr::kRecordSize;
     unwinding_info_header.mapped_size_ = 0;
   }
 
   int content_size = static_cast<int>(sizeof(unwinding_info_header) +
                                       unwinding_info_header.unwinding_size_);
   int padding_size = RoundUp(content_size, 8) - content_size;
   unwinding_info_header.size_ = content_size + padding_size;
 
   LogWriteBytes(reinterpret_cast<const char*>(&unwinding_info_header),
                 sizeof(unwinding_info_header));
 
   if (code->has_unwinding_info()) {
-    // The last EhFrameHdr::kRecordSize bytes were a placeholder for the header.
-    // Discard them and write the actual eh_frame_hdr (below).
-    DCHECK_GE(code->unwinding_info_size(), EhFrameHdr::kRecordSize);
     LogWriteBytes(reinterpret_cast<const char*>(code->unwinding_info_start()),
-                  code->unwinding_info_size() - EhFrameHdr::kRecordSize);
+                  code->unwinding_info_size());
+  } else {
+    EhFrameHdr dummy_eh_frame_hdr = EhFrameHdr::MakeDummy();
+    LogWriteBytes(reinterpret_cast<const char*>(&dummy_eh_frame_hdr),
+                  EhFrameHdr::kRecordSize);
   }
 
-  LogWriteBytes(reinterpret_cast<const char*>(&eh_frame_hdr),
-                EhFrameHdr::kRecordSize);
-
   char padding_bytes[] = "\0\0\0\0\0\0\0\0";
   DCHECK_LT(padding_size, sizeof(padding_bytes));
   LogWriteBytes(padding_bytes, padding_size);
 }
 
 void PerfJitLogger::CodeMoveEvent(AbstractCode* from, Address to) {
   // Code relocation not supported.
   UNREACHABLE();
 }
 
@@ skipping 16 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