Re: [PATCH bpf-next v2 3/3] selftests/bpf: Disable warnings on unused flags for Clang builds

[Jiri Olsa <olsajiri@gmail.com>]

On Fri, Oct 18, 2024 at 08:49:01AM +0200, Viktor Malik wrote:
> There exist compiler flags supported by GCC but not supported by Clang
> (e.g. -specs=...). Currently, these cannot be passed to BPF selftests
> builds, even when building with GCC, as some binaries (urandom_read and
> liburandom_read.so) are always built with Clang and the unsupported
> flags make the compilation fail (as -Werror is turned on).
> 
> Add -Wno-unused-command-line-argument to these rules to suppress such
> errors.
> 
> This allows to do things like:
> 
>     $ CFLAGS="-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1" \
>       make -C tools/testing/selftests/bpf

hi,
might be my fedora setup, but this example gives me compile error below
even with the patch applied:

  EXT-OBJ  [test_progs] testing_helpers.o
In file included from testing_helpers.c:10:
disasm.h:11:10: fatal error: linux/stringify.h: No such file or directory
   11 | #include <linux/stringify.h>
      |          ^~~~~~~~~~~~~~~~~~~

jirka

> 
> Without this patch, the compilation would fail with:
> 
>     [...]
>     clang: error: argument unused during compilation: '-specs=/usr/lib/rpm/redhat/redhat-hardened-cc1' [-Werror,-Wunused-command-line-argument]
>     make: *** [Makefile:273: /bpf-next/tools/testing/selftests/bpf/liburandom_read.so] Error 1
>     [...]
> 
> Signed-off-by: Viktor Malik <vmalik@redhat.com>
> ---
>  tools/testing/selftests/bpf/Makefile | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index 1fc7c38e56b5..3da1a61968b7 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -273,6 +273,7 @@ $(OUTPUT)/liburandom_read.so: urandom_read_lib1.c urandom_read_lib2.c liburandom
>  	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
>  		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) \
>  		     $(filter %.c,$^) $(filter-out -static,$(LDLIBS)) \
> +		     -Wno-unused-command-line-argument \
>  		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>  		     -Wl,--version-script=liburandom_read.map \
>  		     -fPIC -shared -o $@
> @@ -281,6 +282,7 @@ $(OUTPUT)/urandom_read: urandom_read.c urandom_read_aux.c $(OUTPUT)/liburandom_r
>  	$(call msg,BINARY,,$@)
>  	$(Q)$(CLANG) $(CLANG_TARGET_ARCH) \
>  		     $(filter-out -static,$(CFLAGS) $(LDFLAGS)) $(filter %.c,$^) \
> +		     -Wno-unused-command-line-argument \
>  		     -lurandom_read $(filter-out -static,$(LDLIBS)) -L$(OUTPUT) \
>  		     -fuse-ld=$(LLD) -Wl,-znoseparate-code -Wl,--build-id=sha1 \
>  		     -Wl,-rpath=. -o $@
> -- 
> 2.47.0
>