Re: [PATCH] Makefile: use CXXFLAGS for linking fuzzers

From: Stefan Beller <sbeller@google.com>
To: Josh Steadmon <steadmon@google.com>
Cc: git <git@vger.kernel.org>
Subject: Re: [PATCH] Makefile: use CXXFLAGS for linking fuzzers
Date: Mon, 12 Nov 2018 14:47:37 -0800	[thread overview]
Message-ID: <CAGZ79kb68+vxHmwbttvXgaxvPdqAh3vJjZ9+U+BjY7ZeZzOxUA@mail.gmail.com> (raw)
In-Reply-To: <1630a93f8270ca090459be8cc7213221cc6250cf.1542060094.git.steadmon@google.com>

On Mon, Nov 12, 2018 at 2:03 PM <steadmon@google.com> wrote:
>
> OSS-Fuzz requires C++-specific flags to link fuzzers. Passing these in
> CFLAGS causes lots of build warnings. Using separate CXXFLAGS avoids
> this.
>

That makes sense in this context, ....

>  CFLAGS = -g -O2 -Wall
> +CXXFLAGS ?= $(CFLAGS)

... but out of context, just by reading the relevant part of the Makefile,
a user might mistakenly assume we do some C++ trickery for standard
compilation of Git. (Is that bad or do we just not care?)

I wonder if setting the CXXFLAGS near or in the fuzz target
would be better.

>  LDFLAGS =
>  ALL_CFLAGS = $(CPPFLAGS) $(CFLAGS)
>  ALL_LDFLAGS = $(LDFLAGS)
> @@ -3098,14 +3099,14 @@ cover_db_html: cover_db
>  # An example command to build against libFuzzer from LLVM 4.0.0:
>  #
>  # make CC=clang CXX=clang++ \
> -#      CFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
> +#      CXXFLAGS="-fsanitize-coverage=trace-pc-guard -fsanitize=address" \
>  #      LIB_FUZZING_ENGINE=/usr/lib/llvm-4.0/lib/libFuzzer.a \
>  #      fuzz-all
>  #
>  .PHONY: fuzz-all

Maybe here?

>
>  $(FUZZ_PROGRAMS): all
> -       $(QUIET_LINK)$(CXX) $(CFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
> +       $(QUIET_LINK)$(CXX) $(CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
>                 $(XDIFF_OBJS) $(EXTLIBS) git.o $@.o $(LIB_FUZZING_ENGINE) -o $@

Thanks,
Stefan