linux-kernel - Re: [PATCH 2/5] Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL

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Date:	Mon, 15 Feb 2016 12:46:06 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Michal Marek <mmarek@...e.com>,
	linux-arm-kernel@...ts.infradead.org,
	Peter Oberparleiter <oberpar@...ux.vnet.ibm.com>,
	linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/5] Kbuild: disable 'maybe-uninitialized' warning for
 CONFIG_PROFILE_ALL_BRANCHES

On Fri, Feb 12, 2016 at 05:06:19PM +0100, Arnd Bergmann wrote:
> CONFIG_PROFILE_ALL_BRANCHES confuses gcc-5.x to the degree that it prints
> incorrect warnings about a lot of variables that it thinks can be used
> uninitialized, e.g.:
> 
> i2c/busses/i2c-diolan-u2c.c: In function 'diolan_usb_xfer':
> i2c/busses/i2c-diolan-u2c.c:391:16: warning: 'byte' may be used uninitialized in this function
> iio/gyro/itg3200_core.c: In function 'itg3200_probe':
> iio/gyro/itg3200_core.c:213:6: warning: 'val' may be used uninitialized in this function
> leds/leds-lp55xx-common.c: In function 'lp55xx_update_bits':
> leds/leds-lp55xx-common.c:350:6: warning: 'tmp' may be used uninitialized in this function
> misc/bmp085.c: In function 'show_pressure':
> misc/bmp085.c:363:10: warning: 'pressure' may be used uninitialized in this function
> power/ds2782_battery.c: In function 'ds2786_get_capacity':
> power/ds2782_battery.c:214:17: warning: 'raw' may be used uninitialized in this function
> 
> These are all false positives that either rob someone's time when trying
> to figure out whether they are real, or they get people to send wrong
> patches to shut up the warnings.
> 
> Nobody normally wants to run a CONFIG_PROFILE_ALL_BRANCHES kernel in
> production, so disabling the whole class of warnings for this configuration
> has no serious downsides either.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve

> ---
>  Makefile | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/Makefile b/Makefile
> index 9092c16fa6cf..352f55ccc54e 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -617,7 +617,11 @@ KBUILD_CFLAGS	+= $(call cc-option,-fno-delete-null-pointer-checks,)
>  ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
>  KBUILD_CFLAGS	+= -Os $(call cc-disable-warning,maybe-uninitialized,)
>  else
> -KBUILD_CFLAGS	+= -O2
> +ifdef CONFIG_PROFILE_ALL_BRANCHES
> +KBUILD_CFLAGS	+= -O2 $(call cc-disable-warning,maybe-uninitialized,)
> +else
> +KBUILD_CFLAGS   += -O2
> +endif
>  endif
>  
>  # Tell gcc to never replace conditional load with a non-conditional one
> -- 
> 2.7.0