diff mbox series

Makefile: use CXXFLAGS for linking fuzzers

Message ID 1630a93f8270ca090459be8cc7213221cc6250cf.1542060094.git.steadmon@google.com
State New, archived
Headers show
Series Makefile: use CXXFLAGS for linking fuzzers | expand

Commit Message

Josh Steadmon Nov. 12, 2018, 10:02 p.m. UTC
OSS-Fuzz requires C++-specific flags to link fuzzers. Passing these in
CFLAGS causes lots of build warnings. Using separate CXXFLAGS avoids
this.

Signed-off-by: Josh Steadmon <steadmon@google.com>
---
 Makefile | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

Comments

Stefan Beller Nov. 12, 2018, 10:47 p.m. UTC | #1
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
Junio C Hamano Nov. 13, 2018, 3:12 a.m. UTC | #2
steadmon@google.com writes:

> OSS-Fuzz requires C++-specific flags to link fuzzers. Passing these in
> CFLAGS causes lots of build warnings. Using separate CXXFLAGS avoids
> this.

We are not a C++ shop, so allow me to show ignorance about how
projects that are OSS-Fuzz-enabled work.  Do they use one set of
CXXFLAGS when compiling the "real thing" and a separate set (perhaps
one is subset of the other, or perhaps these two just have overlap)
of CXXFLAGS when building to link with the fuzzer?

What I am trying to get at is if this should be CXXFLAGS or
CXX_FUZZER_FLAGS.  If the OSS-Fuzz-enabled C++ projects use one set
of flags for the "main" part of the project (to produce binaries to
be run by the end users) and then link with extra flags to work with
fuzzers, I would imagine that they won't call the latter CXXFLAGS
but call it something else, and we probably should follow suit if
that is the case.

Not that we plan to (re)write the maint part of Git in C++ ever, so
I am personally OK with sacrificing the most generic CXXFLAGS macro
for the sole use of OSS-Fuzz linkage, but I'd prefer to leave the
door open so that other things like OSS-Fuzz that require C++ can be
added like your work does to the project.

Thanks.


> Signed-off-by: Josh Steadmon <steadmon@google.com>
> ---
>  Makefile | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index bbfbb4292d..5462bc4b6b 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -497,6 +497,7 @@ GIT-VERSION-FILE: FORCE
>  # CFLAGS and LDFLAGS are for the users to override from the command line.
>  
>  CFLAGS = -g -O2 -Wall
> +CXXFLAGS ?= $(CFLAGS)
>  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
>  
>  $(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 $@
>  
>  fuzz-all: $(FUZZ_PROGRAMS)
Josh Steadmon Nov. 13, 2018, 6:50 p.m. UTC | #3
On 2018.11.13 12:12, Junio C Hamano wrote:
> steadmon@google.com writes:
> 
> > OSS-Fuzz requires C++-specific flags to link fuzzers. Passing these in
> > CFLAGS causes lots of build warnings. Using separate CXXFLAGS avoids
> > this.
> 
> We are not a C++ shop, so allow me to show ignorance about how
> projects that are OSS-Fuzz-enabled work.  Do they use one set of
> CXXFLAGS when compiling the "real thing" and a separate set (perhaps
> one is subset of the other, or perhaps these two just have overlap)
> of CXXFLAGS when building to link with the fuzzer?
> 
> What I am trying to get at is if this should be CXXFLAGS or
> CXX_FUZZER_FLAGS.  If the OSS-Fuzz-enabled C++ projects use one set
> of flags for the "main" part of the project (to produce binaries to
> be run by the end users) and then link with extra flags to work with
> fuzzers, I would imagine that they won't call the latter CXXFLAGS
> but call it something else, and we probably should follow suit if
> that is the case.
> 
> Not that we plan to (re)write the maint part of Git in C++ ever, so
> I am personally OK with sacrificing the most generic CXXFLAGS macro
> for the sole use of OSS-Fuzz linkage, but I'd prefer to leave the
> door open so that other things like OSS-Fuzz that require C++ can be
> added like your work does to the project.
> 
> Thanks.

OSS-Fuzz only provides one set of CXXFLAGS for use on both compiling
project C++ project files as well linking the fuzzers themselves. So in
the event that Git ever added any C++ sources, they would need to use
the same set of CXXFLAGS.

Given that, do you agree with Stefan that it is more intuitive to define
CXXFLAGS next to the fuzzer build rules, since that's the only place
it's used for now?
Junio C Hamano Nov. 14, 2018, 2:56 a.m. UTC | #4
Josh Steadmon <steadmon@google.com> writes:

> OSS-Fuzz only provides one set of CXXFLAGS for use on both compiling
> project C++ project files as well linking the fuzzers themselves. So in
> the event that Git ever added any C++ sources, they would need to use
> the same set of CXXFLAGS.

OK.

> Given that, do you agree with Stefan that it is more intuitive to define
> CXXFLAGS next to the fuzzer build rules, since that's the only place
> it's used for now?

I am not sure.  Until we gain other C++ targets (in other words,
while linking with fuzzer is the only consumer of CXXFLAGS), I'd
consider it similar to SPARSE_FLAGS and SPATCH_FLAGS, i.e. settings
specific to an auxiliary tool that supports our development process,
and it would make more sense to define it near them higher in the
Makefile.

I'd probably feel differently if this were called FUZZ_CXXFLAGS or
something like that, which would make its natural home next to
the rule to build $(FUZZ_PROGRAMS), though.
diff mbox series

Patch

diff --git a/Makefile b/Makefile
index bbfbb4292d..5462bc4b6b 100644
--- a/Makefile
+++ b/Makefile
@@ -497,6 +497,7 @@  GIT-VERSION-FILE: FORCE
 # CFLAGS and LDFLAGS are for the users to override from the command line.
 
 CFLAGS = -g -O2 -Wall
+CXXFLAGS ?= $(CFLAGS)
 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
 
 $(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 $@
 
 fuzz-all: $(FUZZ_PROGRAMS)