Re: [PATCH v2] Update 'make fuzz-all' docs to reflect modern clang
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From: Junio C Hamano <hidden>
Date: 2021-03-04 22:48:09
"Andrzej Hunt via GitGitGadget" [off-list ref] writes:
From: Andrzej Hunt <redacted>
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.
quoted hunk
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.