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

[Stefan Beller <sbeller@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