[libFuzzer] llvm-objdump doesn't show the same info that objdump on DSO.

[mpividori]

Summary

When disassembling a DSO, for calls to functions from the PLT, llvm-objdump only prints the offset from the PLT, like: <.plt+0x30>.

While objdump and dumpbin print the function name, like: <__sanitizer_cov_trace_pc_guard@plt>

When analyzing the coverage in libFuzzer we dissasemble and look for the calls to __sanitizer_cov_trace_pc_guard.

So, this fails when using llvm-objdump on a DSO.

This was the reason why coverage.test was failing on Windows:

• dumpbin was not considered because of https://reviews.llvm.org/D29371
• llvm-objdump didn't find the calls to __sanitizer_cov_trace_pc_guard in the DLL.

lib/Fuzzer/FuzzerUtilWindows.cpp

if (It[0] == Cpatt[0] && memcmp(It, Cpatt, PattLen) == 0)
       return It;
 
   return NULL;
 }
 
 std::string DisassembleCmd(const std::string &FileName) {
   if (ExecuteCommand("dumpbin /summary > nul") == 0)
     return "dumpbin /disasm " + FileName;
-  if (ExecuteCommand("llvm-objdump > nul") == 0)
-    return "llvm-objdump -d " + FileName;
-  Printf("libFuzzer: couldn't find tool to disassemble (dumpbin, "
-      "llvm-objdump)\n");
+  Printf("libFuzzer: couldn't find tool to disassemble (dumpbin)\n");
   exit(1);
 }
 
 std::string SearchRegexCmd(const std::string &Regex) {
   return "findstr /r \"" + Regex + "\"";
 }
 
 } // namespace fuzzer
 
 #endif // LIBFUZZER_WINDOWS