linux-kernel - Re: [PATCH v2 3/3] selftests/futex: pass _GNU

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Date: Thu, 30 May 2024 13:07:31 -0600
From: Shuah Khan <skhan@...uxfoundation.org>
To: John Hubbard <jhubbard@...dia.com>, Shuah Khan <shuah@...nel.org>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Peter Zijlstra <peterz@...radead.org>, Darren Hart <dvhart@...radead.org>,
 Davidlohr Bueso <dave@...olabs.net>, Edward Liaw <edliaw@...gle.com>,
 André Almeida <andrealmeid@...lia.com>,
 "Nysal Jan K . A" <nysal@...ux.ibm.com>, Mark Brown <broonie@...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 3/3] selftests/futex: pass _GNU_SOURCE without a value
 to the compiler

On 5/28/24 20:29, John Hubbard wrote:
> It's slightly better to set _GNU_SOURCE in the source code, but if one
> must do it via the compiler invocation, then the best way to do so is
> this:
> 
>      $(CC) -D_GNU_SOURCE=
> 
> ...because otherwise, if this form is used:
> 
>      $(CC) -D_GNU_SOURCE
> 
> ...then that leads the compiler to set a value, as if you had passed in:
> 
>      $(CC) -D_GNU_SOURCE=1
> 
> That, in turn, leads to warnings under both gcc and clang, like this:
> 
>      futex_requeue_pi.c:20: warning: "_GNU_SOURCE" redefined
> 
> Fix this by using the "-D_GNU_SOURCE=" form.
> 
> Reviewed-by: Edward Liaw <edliaw@...gle.com>
> Reviewed-by: Davidlohr Bueso <dave@...olabs.net>
> Signed-off-by: John Hubbard <jhubbard@...dia.com>
> ---
>   tools/testing/selftests/futex/functional/Makefile | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/futex/functional/Makefile b/tools/testing/selftests/futex/functional/Makefile
> index a392d0917b4e..994fa3468f17 100644
> --- a/tools/testing/selftests/futex/functional/Makefile
> +++ b/tools/testing/selftests/futex/functional/Makefile
> @@ -1,6 +1,6 @@
>   # SPDX-License-Identifier: GPL-2.0
>   INCLUDES := -I../include -I../../ $(KHDR_INCLUDES)
> -CFLAGS := $(CFLAGS) -g -O2 -Wall -D_GNU_SOURCE -pthread $(INCLUDES) $(KHDR_INCLUDES)
> +CFLAGS := $(CFLAGS) -g -O2 -Wall -D_GNU_SOURCE= -pthread $(INCLUDES) $(KHDR_INCLUDES)
>   LDLIBS := -lpthread -lrt
>   
>   LOCAL_HDRS := \

This looks fine. Applied now to linux-kselftest fixes branch

thanks,
-- Shuah