linux-kernel - Re: [PATCH] perf: fix gcc4.6 build failure with unused-but-set warning

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Date:	Thu, 02 Jun 2011 14:27:28 -0700
From:	Darren Hart <dvhart@...ux.intel.com>
To:	Darren Hart <dvhart@...ux.intel.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Bruce Ashfield <bruce.ashfield@...driver.com>
Subject: Re: [PATCH] perf: fix gcc4.6 build failure with unused-but-set warning

Nevermind, this appears to be user error as the __used directive now
upstream should address this. Apologies.

--
Darren

On 06/02/2011 01:47 PM, Darren Hart wrote:
> I ran into the following build failure with gcc 4.6:
> 
> 	bench/sched-pipe.c: In function 'bench_sched_pipe':
> 	bench/sched-pipe.c:58:6: error: variable 'ret' set but not used
> 	[-Werror=unused-but-set-variable]
> 	cc1: all warnings being treated as errors
> 
> As the main kernel Makefile has added -Wno-unused-but-set-variable
> and sched-pipe.c claims:
> 
> 	/*
> 	 * why does "ret" exist?
> 	 * discarding returned value of read(), write()
> 	 * causes error in building environment for perf
> 	 */
> 
> This patch creates a new perf/Makefile variable, LESS_WARNINGS and
> adds -Wno-unused-but-set-variable. The new variable helps distinguish
> between the added warnings in EXTRA_WARNINGS versus those we want to
> remove, including the existing -Wno-system-headers which I moved to
> LESS_WARNINGS.
> 
> Signed-off-by: Darren Hart <dvhart@...ux.intel.com>
> Cc: Ingo Molnar <mingo@...e.hu>
> Cc: Bruce Ashfield <bruce.ashfield@...driver.com>
> ---
>  tools/perf/Makefile |   10 ++++++++--
>  1 files changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/tools/perf/Makefile b/tools/perf/Makefile
> index 032ba63..fdb35dc 100644
> --- a/tools/perf/Makefile
> +++ b/tools/perf/Makefile
> @@ -74,7 +74,6 @@ EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wredundant-decls
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wstrict-aliasing=3
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wswitch-default
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wswitch-enum
> -EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wno-system-headers
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wundef
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wwrite-strings
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wbad-function-cast
> @@ -85,6 +84,13 @@ EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wold-style-definition
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wstrict-prototypes
>  EXTRA_WARNINGS := $(EXTRA_WARNINGS) -Wdeclaration-after-statement
>  
> +#
> +# Disable warnings that cause build problems or needlessly polute output:
> +#
> +
> +LESS_WARNINGS := -Wno-system-headers
> +LESS_WARNINGS := $(LESS_WARNINGS) -Wno-unused-but-set-variable
> +
>  ifeq ("$(origin DEBUG)", "command line")
>    PERF_DEBUG = $(DEBUG)
>  endif
> @@ -92,7 +98,7 @@ ifndef PERF_DEBUG
>    CFLAGS_OPTIMIZE = -O6
>  endif
>  
> -CFLAGS = -fno-omit-frame-pointer -ggdb3 -Wall -Wextra -std=gnu99 -Werror $(CFLAGS_OPTIMIZE) -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS) $(EXTRA_CFLAGS)
> +CFLAGS = -fno-omit-frame-pointer -ggdb3 -Wall -Wextra -std=gnu99 -Werror $(CFLAGS_OPTIMIZE) -D_FORTIFY_SOURCE=2 $(EXTRA_WARNINGS) $(LESS_WARNINGS) $(EXTRA_CFLAGS)
>  EXTLIBS = -lpthread -lrt -lelf -lm
>  ALL_CFLAGS = $(CFLAGS) -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64
>  ALL_LDFLAGS = $(LDFLAGS)

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel
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