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

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Date: Thu, 30 May 2024 12:28:14 -0700
From: John Hubbard <jhubbard@...dia.com>
To: Shuah Khan <skhan@...uxfoundation.org>, Shuah Khan <shuah@...nel.org>
Cc: 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,
 Nathan Chancellor <nathan@...nel.org>
Subject: Re: [PATCH 2/2] selftests/lib.mk: silence some clang warnings that
 gcc already ignores

On 5/30/24 7:25 AM, Shuah Khan wrote:
> On 5/28/24 20:08, John Hubbard wrote:
>> gcc defaults to silence (off) for the following warnings, but clang
>> defaults to the opposite. These warnings are not useful for kselftests,
>> so silence them for the clang builds as well:
> 
> Please you add more information on why they aren't useful
> for kselftests.

Ah OK. My wording is a little misleading. The warnings are not useful
for the *kernel*, as previous decided by the gcc settings when building
the kernel. And it is only only due to including kernel data structures
in the selftests, that we get the warnings on clang.

So it is not something 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.

I can post a v2 to update both the comment and the commit description.


thanks,
-- 
John Hubbard
NVIDIA

> 
>>
>>      -Wno-address-of-packed-member
>>      -Wno-gnu-variable-sized-type-not-at-end
>>
>> 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>
>> ---
>>   tools/testing/selftests/lib.mk | 6 ++++++
>>   1 file changed, 6 insertions(+)
>>
>> diff --git a/tools/testing/selftests/lib.mk 
>> b/tools/testing/selftests/lib.mk
>> index 2902787b89b2..41e879f3f8a2 100644
>> --- a/tools/testing/selftests/lib.mk
>> +++ b/tools/testing/selftests/lib.mk
>> @@ -50,6 +50,12 @@ 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. These warnings are not useful for kselftests, so 
>> silence them
>> +# for the clang builds as well.
>> +CFLAGS += -Wno-address-of-packed-member
>> +CFLAGS += -Wno-gnu-variable-sized-type-not-at-end
>> +
>>   CC := $(CLANG) $(CLANG_FLAGS) -fintegrated-as
>>   else
>>   CC := $(CROSS_COMPILE)gcc
> 
> thanks,
> -- Shuah
>