[all-commits] [llvm/llvm-project] f7ffb1: [libFuzzer] Instrument bcmp

[Fangrui Song via All-commits]

  Branch: refs/heads/master
  Home:   https://github.com/llvm/llvm-project
  Commit: f7ffb122d08e7a8203557898c67eaac3a857b152
      https://github.com/llvm/llvm-project/commit/f7ffb122d08e7a8203557898c67eaac3a857b152
  Author: Fangrui Song <maskray at google.com>
  Date:   2020-07-24 (Fri, 24 Jul 2020)

  Changed paths:
    M compiler-rt/lib/fuzzer/FuzzerInterceptors.cpp
    M compiler-rt/test/fuzzer/MemcmpTest.cpp
    A compiler-rt/test/fuzzer/bcmp.test

  Log Message:
  -----------
  [libFuzzer] Instrument bcmp

If we define memcmp in an archive, bcmp should be defined as well (many libc
define bcmp/memcmp in one object file).  Otherwise if the application calls bcmp
or strcmp which gets optimized to bcmp (SimplifyLibCalls), the undefined
reference may pull in an optimized bcmp/strcmp implementation (libc replacement)
later on the linker command line.  If both libFuzzer's memcmp and the optimized
memcmp are strong => there will be a multiple definition error.