Re: [PATCH v2] selftests/net: suppress clang's "variable-sized type not at the end" warning

[Nathan Chancellor <nathan@kernel.org>]

On Mon, May 27, 2024 at 02:36:41PM -0700, John Hubbard wrote:
> When building with clang, via:
> 
>     make LLVM=1 -C tools/testing/selftest
> 
> ...clang warns that "a variable sized type not at the end of a struct or
> class is a GNU extension".
> 
> These cases are not easily changed, because they involve structs that
> are part of the API. Fortunately, however, the tests seem to be doing
> just fine (specifically, neither affected test runs any differently with
> gcc vs. clang builds, on my test system) regardless of the warning. So,
> all the warning is doing is preventing a clean build of selftests/net.
> 
> Fix this by suppressing this particular clang warning for the
> selftests/net suite.
> 
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
> 
> Changes since the first version:
> 
> 1) Rebased onto Linux 6.10-rc1
> 
> thanks,
> John Hubbard
> 
> 
>  tools/testing/selftests/net/Makefile | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/tools/testing/selftests/net/Makefile b/tools/testing/selftests/net/Makefile
> index bd01e4a0be2c..9a3b766c8781 100644
> --- a/tools/testing/selftests/net/Makefile
> +++ b/tools/testing/selftests/net/Makefile
> @@ -6,6 +6,10 @@ CFLAGS += -I../../../../usr/include/ $(KHDR_INCLUDES)
>  # Additional include paths needed by kselftest.h
>  CFLAGS += -I../
>  
> +ifneq ($(LLVM),)
> +    CFLAGS += -Wno-gnu-variable-sized-type-not-at-end

For what it's worth, the main kernel has -Wno-gnu because there is
little point in warning about the use of GNU extensions when building
with '-std=gnu...'. It may be worth doing this anywhere that uses a GNU
standard in the selftests but I guess it depends on how noisy things
are.

> +endif
> +
>  TEST_PROGS := run_netsocktests run_afpackettests test_bpf.sh netdevice.sh \
>  	      rtnetlink.sh xfrm_policy.sh test_blackhole_dev.sh
>  TEST_PROGS += fib_tests.sh fib-onlink-tests.sh pmtu.sh udpgso.sh ip_defrag.sh
> 
> base-commit: 2bfcfd584ff5ccc8bb7acde19b42570414bf880b
> -- 
> 2.45.1
> 
>