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

[Jiri Olsa <olsajiri@gmail.com>]

On Mon, Oct 21, 2024 at 08:20:39AM +0200, Viktor Malik wrote:
> On 10/20/24 19:24, Jiri Olsa wrote:
> > 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>
> >       |          ^~~~~~~~~~~~~~~~~~~
> 
> Aren't you doing `make CFLAGS="..."` instead of `CFLAGS="..." make`? The
> difference is that the former overrides CFLAGS defined in selftests
> Makefile and therefore the include dirs are not correctly added.

right, I was doing that, thanks

Acked-by: Jiri Olsa <jolsa@kernel.org>

jirka

> 
> > 
> > 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
> >>
> > 
>