Subject: Re: [PATCH v3] Makefile: update 'make fuzz-all' docs to reflect modern clang

From: Josh Steadmon <[email-masked]>
Date: Wed, 10 Mar 2021 10:52:39 -0800

On 2021.03.08 17:14, Andrzej Hunt via GitGitGadget wrote:
> From: Andrzej Hunt <[email-masked]>
> 
> Clang no longer produces a libFuzzer.a. Instead, you can include
> libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in
> the example command for building fuzzers.
> 
> We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all
> the required instrumentation is added when compiling git [1], and remove
>  -fsanitize-coverage=trace-pc-guard as it is deprecated.
> 
> I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears
> to work in a wide range of reasonably modern clangs.
> 
> (On my system: what used to be libFuzzer.a now lives under the following
>  path, which is tricky albeit not impossible for a novice such as myself
>  to find:
> /usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
> 
> [1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage
> 
> Signed-off-by: Andrzej Hunt <[email-masked]>
> ---
>     Update 'make fuzz-all' docs to reflect modern clang
>     
>     This version of the patch fixes the commit message as per Junio's
>     feedback. Thank you!
> 
> Published-As: https://github.com/gitgitgadget/git/releases/tag/pr-889%2Fahunt%2Ffuzz-docs-v3
> Fetch-It-Via: git fetch https://github.com/gitgitgadget/git pr-889/ahunt/fuzz-docs-v3
> Pull-Request: https://github.com/gitgitgadget/git/pull/889
> 
> Range-diff vs v2:
> 
>  1:  f5b5a11966ca ! 1:  bc0d8b615410 Update 'make fuzz-all' docs to reflect modern clang
>      @@ Metadata
>       Author: Andrzej Hunt <[email-masked]>
>       
>        ## Commit message ##
>      -    Update 'make fuzz-all' docs to reflect modern clang
>      +    Makefile: update 'make fuzz-all' docs to reflect modern clang
>       
>      -    Clang no longer produces a libFuzzer.a, instead you can include
>      -    libFuzzer by using -fsanitize=fuzzer. Therefore we should use
>      -    that in the example command for building fuzzers.
>      +    Clang no longer produces a libFuzzer.a. Instead, you can include
>      +    libFuzzer by using -fsanitize=fuzzer. Therefore we should use that in
>      +    the example command for building fuzzers.
>       
>      -    We also add -fsanitize=fuzzer-no-link to ensure that all the required
>      -    instrumentation is added when compiling git [1], and remove
>      +    We also add -fsanitize=fuzzer-no-link to the CFLAGS to ensure that all
>      +    the required instrumentation is added when compiling git [1], and remove
>            -fsanitize-coverage=trace-pc-guard as it is deprecated.
>       
>      -    I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears to
>      -    work in a wide range of reasonably modern clangs.
>      +    I happen to have tested with LLVM 11 - however -fsanitize=fuzzer appears
>      +    to work in a wide range of reasonably modern clangs.
>       
>      -    (On my system: what used to be libFuzzer.a now lives under the following path,
>      -     which is tricky albeit not impossible for a novice such as myself to find:
>      +    (On my system: what used to be libFuzzer.a now lives under the following
>      +     path, which is tricky albeit not impossible for a novice such as myself
>      +     to find:
>           /usr/lib64/clang/11.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a )
>       
>           [1] https://releases.llvm.org/11.0.0/docs/LibFuzzer.html#fuzzer-usage
> 
> 
>  Makefile | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index dfb0f1000fa3..f3dc2178324e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -3299,11 +3299,11 @@ cover_db_html: cover_db
>  # are not necessarily appropriate for general builds, and that vary greatly
>  # depending on the compiler version used.
>  #
> -# An example command to build against libFuzzer from LLVM 4.0.0:
> +# An example command to build against libFuzzer from LLVM 11.0.0:
>  #
>  # make CC=clang CXX=clang++ \
> -#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
> -#      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
> +#      CFLAGS="-fsanitize=fuzzer-no-link,address" \
> +#      LIB_FUZZING_ENGINE="-fsanitize=fuzzer" \
>  #      fuzz-all
>  #
>  FUZZ_CXXFLAGS ?= $(CFLAGS)
> 
> base-commit: be7935ed8bff19f481b033d0d242c5d5f239ed50
> -- 
> gitgitgadget

This version looks good to me, although you may also want to make the
changes Junio suggested regarding LIB_FUZZING_ENGINE.

Thanks!