"Andrzej Hunt via GitGitGadget" <gitgitgadget@xxxxxxxxx> writes:
> From: Andrzej Hunt <ajrhunt@xxxxxxxxxx>
> Subject: Re: [PATCH v2] Update 'make fuzz-all' docs to reflect modern clang
I'd retitte it to
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.
Do we see two sentences here? IOW, s/, instead/. Instead/ is needed?
> 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
> -fsanitize-coverage=trace-pc-guard as it is deprecated.
Without something like s/add/add to CFLAGS/, I found this a bit
cryptic and failed to read what it wanted to do without looking at
the patch text itself.
> 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 )
All nice things to have in the log message.
> Makefile | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index dd08b4ced01c..c7248ac6057b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -3292,11 +3292,11 @@ 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)
LIB_FUZZING_ENGINE is used this way in the Makefile:
$(FUZZ_PROGRAMS): all
$(QUIET_LINK)$(CXX) $(FUZZ_CXXFLAGS) $(LIB_OBJS) $(BUILTIN_OBJS) \
$(XDIFF_OBJS) $(EXTLIBS) git.o $@.o $(LIB_FUZZING_ENGINE) -o $@
and it is somewhat annoying to see a compiler/linker option that
late on the command line, where readers would expect an object file
or a library archive would appear. It makes me wonder if we should
instead be doing something along the following line:
- empty LIB_FUZZING_ENGINE by default
- add -fsanitize=fuzzer names to FUZZ_CXXFLAGS
i.e.
diff --git c/Makefile w/Makefile
index 4128b457e1..b5df76b33b 100644
--- c/Makefile
+++ w/Makefile
@@ -3306,14 +3306,15 @@ 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" \
# fuzz-all
#
FUZZ_CXXFLAGS ?= $(CFLAGS)
+FUZZ_CXXFLAGS += -fsanitize=fuzzer
+LIB_FUZZING_ENGINE =
.PHONY: fuzz-all
In the meantime, I'll queue the version you sent as-is (modulo the
retitling).
Thanks.
