linux-kernel - Re: [PATCH v2 2/2] selftests/lib.mk: silence some clang warnings that gcc already ignores

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Date: Fri, 7 Jun 2024 11:23:30 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: Nathan Chancellor <nathan@...nel.org>, John Hubbard <jhubbard@...dia.com>
Cc: Shuah Khan <shuah@...nel.org>,
 Muhammad Usama Anjum <usama.anjum@...labora.com>,
 Beau Belgrave <beaub@...ux.microsoft.com>,
 Steven Rostedt <rostedt@...dmis.org>, Mark Brown <broonie@...nel.org>,
 Naresh Kamboju <naresh.kamboju@...aro.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>,
 Justin Stitt <justinstitt@...gle.com>, Bill Wendling <morbo@...gle.com>,
 sunliming <sunliming@...inos.cn>, Masami Hiramatsu <mhiramat@...nel.org>,
 Valentin Obst <kernel@...entinobst.de>, linux-kselftest@...r.kernel.org,
 LKML <linux-kernel@...r.kernel.org>, llvm@...ts.linux.dev,
 Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2 2/2] selftests/lib.mk: silence some clang warnings that
 gcc already ignores

On 6/3/24 16:36, Nathan Chancellor wrote:
> On Fri, May 31, 2024 at 11:37:51AM -0700, John Hubbard wrote:
>> gcc defaults to silence (off) for the following warnings, but clang
>> defaults to the opposite. The warnings are not useful for the kernel
>> itself, which is why they have remained disabled in gcc for the main
>> kernel build. And it is only due to including kernel data structures in
>> the selftests, that we get the warnings from clang.
>>
>>      -Waddress-of-packed-member
>>      -Wgnu-variable-sized-type-not-at-end
>>
>> In other words, the warnings are not unique to the selftests: there is
>> nothing that the selftests' code does that triggers these warnings,
>> other than the act of including the kernel's data structures. Therefore,
>> silence them for the clang builds as well.
>>
>> This eliminates warnings for the net/ and user_events/ kselftest
>> subsystems, in these files:
>>
>>      ./net/af_unix/scm_rights.c
>>      ./net/timestamping.c
>>      ./net/ipsec.c
>>      ./user_events/perf_test.c
>>
>> Cc: Nathan Chancellor <nathan@...nel.org>
>> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> 
> This seems reasonable to me.
> 
> Acked-by: Nathan Chancellor <nathan@...nel.org>
> 
>> ---
>>   tools/testing/selftests/lib.mk | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/tools/testing/selftests/lib.mk b/tools/testing/selftests/lib.mk
>> index 2902787b89b2..c179c02281e9 100644
>> --- a/tools/testing/selftests/lib.mk
>> +++ b/tools/testing/selftests/lib.mk
>> @@ -50,6 +50,14 @@ else
>>   CLANG_FLAGS     += --target=$(notdir $(CROSS_COMPILE:%-=%))
>>   endif # CROSS_COMPILE
>>   
>> +# gcc defaults to silence (off) for the following warnings, but clang defaults
>> +# to the opposite. The warnings are not useful for the kernel itself, which is
>> +# why they have remained disabled in gcc for the main kernel build. And it is
>> +# only due to including kernel data structures in the selftests, that we get the
>> +# warnings from clang. Therefore, disable the warnings for clang builds.
>> +CFLAGS += -Wno-address-of-packed-member
>> +CFLAGS += -Wno-gnu-variable-sized-type-not-at-end
>> +

Thank you for adding this comment block.

>>   CC := $(CLANG) $(CLANG_FLAGS) -fintegrated-as
>>   else
>>   CC := $(CROSS_COMPILE)gcc
>> -- 
>> 2.45.1
>>
>>
> 

Thank you both. I will apply this for the next release. I want this
change soaking in next for a bit.

thanks,
-- Shuah