netdev - Re: [PATCH bpf-next] selftests/bpf: suppress readelf stderr when probing for BTF support

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Date:   Wed, 23 Jan 2019 17:45:29 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Stanislav Fomichev <sdf@...gle.com>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, ast@...nel.org,
        daniel@...earbox.net
Subject: Re: [PATCH bpf-next] selftests/bpf: suppress readelf stderr when
 probing for BTF support

On Wed, Jan 23, 2019 at 09:24:35AM -0800, Stanislav Fomichev wrote:
> Before:
> $ make -s -C tools/testing/selftests/bpf
> readelf: Error: Missing knowledge of 32-bit reloc types used in DWARF
> sections of machine number 247
> readelf: Warning: unable to apply unsupported reloc type 10 to section
> .debug_info
> readelf: Warning: unable to apply unsupported reloc type 1 to section
> .debug_info
> readelf: Warning: unable to apply unsupported reloc type 10 to section
> .debug_info
> 
> After:
> $ make -s -C tools/testing/selftests/bpf
> 
> Signed-off-by: Stanislav Fomichev <sdf@...gle.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 70229de510f5..ff3cab5525c1 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -131,7 +131,7 @@ BTF_PAHOLE_PROBE := $(shell $(BTF_PAHOLE) --help 2>&1 | grep BTF)
>  BTF_OBJCOPY_PROBE := $(shell $(LLVM_OBJCOPY) --help 2>&1 | grep -i 'usage.*llvm')
>  BTF_LLVM_PROBE := $(shell echo "int main() { return 0; }" | \
>  			  $(CLANG) -target bpf -O2 -g -c -x c - -o ./llvm_btf_verify.o; \
> -			  readelf -S ./llvm_btf_verify.o | grep BTF; \
> +			  readelf -S ./llvm_btf_verify.o 2>/dev/null | grep BTF; \
>  			  /bin/rm -f ./llvm_btf_verify.o)

Silencing the warning may hide real issue later.
I'd rather fix whatever is necessary in readelf.
Does it use bfd? if so bpf support for bfd was practically complete.