Re: [PATCH bpf-next 3/5] selftests/bpf: fix test_cpp compilation failure with clang

[Andrii Nakryiko <andrii.nakryiko@gmail.com>]

On Sat, Apr 10, 2021 at 9:49 AM Yonghong Song <yhs@fb.com> wrote:
>
> With clang compiler:
>   make -j60 LLVM=1 LLVM_IAS=1  <=== compile kernel
>   make -j60 -C tools/testing/selftests/bpf LLVM=1 LLVM_IAS=1
> the test_cpp build failed due to the failure:
>   warning: treating 'c-header' input as 'c++-header' when in C++ mode, this behavior is deprecated [-Wdeprecated]
>   clang-13: warning: cannot specify -o when generating multiple output files
>
> test_cpp compilation flag looks like:
>   clang++ -g -Og -rdynamic -Wall -I<...> ... \
>   -Dbpf_prog_load=bpf_prog_test_load -Dbpf_load_program=bpf_test_load_program \
>   test_cpp.cpp <...>/test_core_extern.skel.h <...>/libbpf.a <...>/test_stub.o \
>   -lcap -lelf -lz -lrt -lpthread -o <...>/test_cpp
>
> The clang++ compiler complains the header file in the command line.
> Let us remove the header file from the command line which is not intended
> any way, and this fixed the problem.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---
>  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 6448c626498f..bbd61cc3889b 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -481,7 +481,7 @@ $(OUTPUT)/test_verifier: test_verifier.c verifier/tests.h $(BPFOBJ) | $(OUTPUT)
>  # 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) $^ $(LDLIBS) -o $@
> +       $(Q)$(CXX) $(CFLAGS) test_cpp.cpp $(BPFOBJ) $(LDLIBS) -o $@

see what we do for other binaries:

$(filter %.a %.o %.c,$^)

It's more generic. Add %.cpp, of course.

>
>  # Benchmark runner
>  $(OUTPUT)/bench_%.o: benchs/bench_%.c bench.h
> --
> 2.30.2
>