From: Andrzej Hunt <andrzej@ahunt.org>
Date: Thu, 04 Mar 2021 15:26:21 GMT
Subject: Re: [PATCH] Update 'make fuzz-all' docs to reflect modern clang
Message-ID: <094d75bf-707a-5b0d-fead-5c9ad08e0a18@ahunt.org>
In-Reply-To: <YD1tJlY/mqZOmTNm@google.com>

On 01/03/2021 23:39, Josh Steadmon wrote:
> Thanks for taking a look at this! This looked correct to me, but when I
> tried to run the fuzzers I got an error about
> "-fsanitize-coverage=trace-pc-guard" not being supported any longer.

Oops, I realised I was accidentally using clang 7 (instead of 11) 
locally. I can reproduce the same error with my copy of clang-11. Thanks 
for catching this!

> Looking at the LLVM 11.0.0 docs [1], I see that it recommends using
> "-fsanitize=fuzzer-no-link" instead (the "-no-link" is because we're
> also building executables that have their own main()).
> 
> So we'd also want to change CFLAGS to
> "-fsanitize=fuzzer-no-link,address".

I will fix this too!

I suspect that when I built without fuzzer-no-link, the fuzzer binaries 
included libFuzzer, but were missing whatever fuzzing-related
instrumentation clang should have added. (Fortunately oss-fuzz seems to
be adding this to the CFLAGS automatically [1].)

[1] 
https://oss-fuzz-build-logs.storage.googleapis.com/log-74f40f33-f384-475b-b141-0e44afb272f5.txt