Re: [PATCH bpf-next v3 4/5] selftests/bpf: silence clang compilation warnings

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

On Tue, Apr 13, 2021 at 8:34 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
> Some linker flags are not used/effective for some binaries and
> we have warnings like:
>   warning: -lelf: 'linker' input unused [-Wunused-command-line-argument]
>
> We also have warnings like:
>   .../selftests/bpf/prog_tests/ns_current_pid_tgid.c:74:57: note: treat the string as an argument to avoid this
>         if (CHECK(waitpid(cpid, &wstatus, 0) == -1, "waitpid", strerror(errno)))
>                                                                ^
>                                                                "%s",
>   .../selftests/bpf/test_progs.h:129:35: note: expanded from macro 'CHECK'
>         _CHECK(condition, tag, duration, format)
>                                          ^
>   .../selftests/bpf/test_progs.h:108:21: note: expanded from macro '_CHECK'
>                 fprintf(stdout, ##format);                              \
>                                   ^
> The first warning can be silenced with clang option -Wno-unused-command-line-argument.
> For the second warning, source codes are modified as suggested by the compiler
> to silence the warning. Since gcc does not support the option
> -Wno-unused-command-line-argument and the warning only happens with clang
> compiler, the option -Wno-unused-command-line-argument is enabled only when
> clang compiler is used.
>
> Signed-off-by: Yonghong Song <yhs@fb.com>
> ---

LGTM, please see the question below.

Acked-by: Andrii Nakryiko <andrii@kernel.org>

>  tools/testing/selftests/bpf/Makefile                         | 5 +++++
>  tools/testing/selftests/bpf/prog_tests/fexit_sleep.c         | 4 ++--
>  tools/testing/selftests/bpf/prog_tests/ns_current_pid_tgid.c | 4 ++--
>  3 files changed, 9 insertions(+), 4 deletions(-)
>
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index dcc2dc1f2a86..c45ae13b88a0 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -28,6 +28,11 @@ CFLAGS += -g -Og -rdynamic -Wall $(GENFLAGS) $(SAN_CFLAGS)           \
>           -Dbpf_load_program=bpf_test_load_program
>  LDLIBS += -lcap -lelf -lz -lrt -lpthread
>
> +# Silence some warnings when compiled with clang
> +ifneq ($(LLVM),)

This won't handle the case where someone does `make CC=clang`, right?
Do we care at all?


> +CFLAGS += -Wno-unused-command-line-argument
> +endif
> +

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