linux-kernel - Re: [PATCH 07/52] tools/perf/build: Split out feature check: 'volatile-register-var'

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Date:	Thu, 10 Oct 2013 14:55:57 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Arnaldo Carvalho de Melo <acme@...hat.com>,
	David Ahern <dsahern@...il.com>, Jiri Olsa <jolsa@...hat.com>
Subject: Re: [PATCH 07/52] tools/perf/build: Split out feature check: 'volatile-register-var'

On Tue,  8 Oct 2013 12:10:37 +0200, Ingo Molnar wrote:
> -ifeq ($(call try-cc,$(SOURCE_HELLO),$(CFLAGS) -Werror -Wvolatile-register-var,-Wvolatile-register-var),y)
> +ifeq ($(feature-volatile-register-var), 1)
>    CFLAGS += -Wvolatile-register-var
>  endif
>  
> diff --git a/tools/perf/config/feature-checks/Makefile b/tools/perf/config/feature-checks/Makefile
> index 46b7650..5693299 100644
> --- a/tools/perf/config/feature-checks/Makefile
> +++ b/tools/perf/config/feature-checks/Makefile
> @@ -3,6 +3,7 @@ FILES=					\
>  	test-hello			\
>  	test-stackprotector-all		\
>  	test-stackprotector		\
> +	test-volatile-register-var	\
>  	test-libnuma
>  
>  CC := $(CC) -MD
> @@ -22,6 +23,9 @@ test-stackprotector-all:
>  test-stackprotector:
>  	$(BUILD) -Werror -fstack-protector
>  
> +test-volatile-register-var:
> +	$(BUILD) -Werror -Wvolatile-register-var

I'm not sure this test is necessary at all.

The gcc manpage says this warning is enabled by -Wall, and we add -Wall
to CFLAGS before doing feature checks.  So all gcc versions that support
-Wvolatile-register-var enables it by default without this check and
older gcc versions will always fail the feature check.

Thanks,
Namhyung
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