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

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Date: Tue, 28 May 2024 13:39:41 -0700
From: Nathan Chancellor <nathan@...nel.org>
To: John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>, "David S . Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Steffen Klassert <steffen.klassert@...unet.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Andreas Färber <afaerber@...e.de>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Matthieu Baerts <matttbe@...nel.org>,
	Mat Martineau <martineau@...nel.org>,
	Geliang Tang <geliang@...nel.org>,
	Pravin B Shelar <pshelar@....org>,
	Willem de Bruijn <willemdebruijn.kernel@...il.com>,
	Alexander Mikhalitsyn <alexander@...alicyn.com>,
	zhujun2 <zhujun2@...s.chinamobile.com>,
	Petr Machata <petrm@...dia.com>, Ido Schimmel <idosch@...dia.com>,
	Hangbin Liu <liuhangbin@...il.com>,
	Nikolay Aleksandrov <razor@...ckwall.org>,
	Benjamin Poirier <bpoirier@...dia.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
	Dmitry Safonov <0x7f454c46@...il.com>, netdev@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-actions@...ts.infradead.org, mptcp@...ts.linux.dev,
	dev@...nvswitch.org, Valentin Obst <kernel@...entinobst.de>,
	linux-kselftest@...r.kernel.org,
	LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev
Subject: Re: [PATCH v2] selftests/net: suppress clang's "variable-sized type
 not at the end" warning

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@...dia.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
> 
>