[llvm-dev] Building LLVM's fuzzers

[Justin Bogner via llvm-dev]

George Karpenkov <ekarpenkov at apple.com> writes:
> Should -DCMAKE_CXX_COMPILER be also specified?

CMake is smart enough to infer that from C_COMPILER:

  % grep CMAKE_CXX_COMPILER CMakeCache.txt
  CMAKE_CXX_COMPILER:FILEPATH=/Users/bogner/llvm-lkgc/bin/clang++

>> On Aug 24, 2017, at 11:29 AM, Justin Bogner <mail at justinbogner.com> wrote:
>> 
>> (kcc, george: sorry for the re-send, the first was from a non-list email
>> address)
>> 
>> My configuration for building the fuzzers in the LLVM tree doesn't seem to
>> work any more (possibly as of moving libFuzzer to compiler-rt, but there
>> have been a few other changes in the last week or so that may be related).
>> 
>> I'm building with a fresh top-of-tree clang and setting
>> -DLLVM_USE_SANITIZER=Address and -DLLVM_USE_SANITIZE_COVERAGE=On, which
>> was working before:
>> 
>>  % cmake -GNinja \
>>          -DCMAKE_BUILD_TYPE=Release -DLLVM_ENABLE_ASSERTIONS=On \
>>          -DLLVM_ENABLE_WERROR=On \
>>          -DLLVM_USE_SANITIZER=Address -DLLVM_USE_SANITIZE_COVERAGE=On \
>>          -DCMAKE_C_COMPILER=$HOME/llvm-lkgc/bin/clang \
>>          $HOME/code/llvm-src
>> 
>> But when I run any of the fuzzers, it looks like the sanitizer coverage
>> hasn't been set up correctly:
>> 
>>  % ./bin/llvm-as-fuzzer                                                                                   2017-08-24 11:14:33
>>  INFO: Seed: 4089166883
>>  INFO: Loaded 1 modules   (50607 guards): 50607 [0x10e14ef80, 0x10e18063c),
>>  INFO: Loaded 1 PC tables (0 PCs): 0 [0x10e2870a8,0x10e2870a8),
>>  ERROR: The size of coverage PC tables does not match the number of instrumented PCs. This might be a bug in the compiler, please contact the libFuzzer developers.
>> 
>> From the build logs, it looks like we're now building objects with these
>> sanitizer flags:
>> 
>>  -fsanitize=address
>>  -fsanitize-address-use-after-scope
>>  -fsanitize=fuzzer-no-link
>> 
>> We're then linking the fuzzer binaries with these:
>> 
>>  -fsanitize=address
>>  -fsanitize-address-use-after-scope
>>  -fsanitize=fuzzer-no-link
>>  -fsanitize=fuzzer
>> 
>> Any idea what's wrong or where to start looking?