patchUpdate 'make fuzz-all' docs to reflect modern clang

> From: Andrzej Hunt <ajrhunt@google.com>
> 
> 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.
> 
> 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 )
> 
> Signed-off-by: Andrzej Hunt <ajrhunt@google.com>
> ---
>     Update 'make fuzz-all' docs to reflect modern clang
>     
>     I would like to update the examples for 'make fuzz-all' to make it
>     easier to build fuzzers locally.
>     
>     This change should make it easier for the uninitiated to build fuzzers
>     locally without first having to figure out what LIB_FUZZING_ENGINE is
>     for.
>     
>     ATB, Andrzej

> Looking at the LLVM 11.0.0 docs [1], I see that it recommends using
> "-fsanitize=fuzzer-no-link" instead (the "-no-link" is because we're
> also building executables that have their own main()).
> 
> So we'd also want to change CFLAGS to
> "-fsanitize=fuzzer-no-link,address".

> 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.

> 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 )

>  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

> However I would prefer to wait for Josh's feedback before making such
> a change, as he is the owner of oss-fuzz's git integration [1], and as 
> such is most likely to be affected by any changes to this target.
>
>
> In the meantime I'll prepare an updated patch with a fixed commit message!

> "Andrzej Hunt via GitGitGadget" <gitgitgadget@gmail.com> writes:
> 
> > From: Andrzej Hunt <ajrhunt@google.com>
> 
> > 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.
> 
> 

> From: Andrzej Hunt <ajrhunt@google.com>
> 
> 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 <ajrhunt@google.com>
> ---
>     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 <ajrhunt@google.com>
>       
>        ## 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