On Thu, Jul 25, 2024 at 2:40 PM Stanislav Fomichev <sdf@xxxxxxxxxxx> wrote:
>
> Jakub reports build failures when merging linux/master with net tree:
>
> CXX test_cpp
> In file included from <built-in>:454:
> <command line>:2:9: error: '_GNU_SOURCE' macro redefined [-Werror,-Wmacro-redefined]
> 2 | #define _GNU_SOURCE
> | ^
> <built-in>:445:9: note: previous definition is here
> 445 | #define _GNU_SOURCE 1
>
> The culprit is commit cc937dad85ae ("selftests: centralize -D_GNU_SOURCE= to
> CFLAGS in lib.mk") which unconditionally added -D_GNU_SOUCE to CLFAGS.
> Apparently clang++ also unconditionally adds it for the C++ targets [0]
> which causes a conflict. Add small change in the selftests makefile
> to filter it out for test_cpp.
>
> Not sure which tree it should go via, targeting bpf for now, but net
> might be better?
>
> 0: https://stackoverflow.com/questions/11670581/why-is-gnu-source-defined-by-default-and-how-to-turn-it-off
>
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Signed-off-by: Stanislav Fomichev <sdf@xxxxxxxxxxx>
> ---
> tools/testing/selftests/bpf/Makefile | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index dd49c1d23a60..81d4757ecd4c 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -713,7 +713,7 @@ $(OUTPUT)/xdp_features: xdp_features.c $(OUTPUT)/network_helpers.o $(OUTPUT)/xdp
> # Make sure we are able to include and link libbpf against c++.
> $(OUTPUT)/test_cpp: test_cpp.cpp $(OUTPUT)/test_core_extern.skel.h $(BPFOBJ)
> $(call msg,CXX,,$@)
> - $(Q)$(CXX) $(CFLAGS) $(filter %.a %.o %.cpp,$^) $(LDLIBS) -o $@
> + $(Q)$(CXX) $(subst -D_GNU_SOURCE=,,$(CFLAGS)) $(filter %.a %.o %.cpp,$^) $(LDLIBS) -o $@
or we could
#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif
(though we have 61 places with that...) so as to not have to update
every target in Makefile.
>
> # Benchmark runner
> $(OUTPUT)/bench_%.o: benchs/bench_%.c bench.h $(BPFOBJ)
> --
> 2.45.2
>
