[PATCH] D29372: [libFuzzer] llvm-objdump doesn't show the same info that objdump on DSO.

Marcos Pividori via Phabricator via llvm-commits llvm-commits at lists.llvm.org
Tue Jan 31 21:36:07 PST 2017

mpividori created this revision.

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 at 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.



Index: lib/Fuzzer/FuzzerUtilWindows.cpp
--- lib/Fuzzer/FuzzerUtilWindows.cpp
+++ lib/Fuzzer/FuzzerUtilWindows.cpp
@@ -181,10 +181,7 @@
 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");

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