2015-11-23 16:27:28

by Arnd Bergmann

Subject: [PATCH] Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES

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 <[email protected]>

diff --git a/Makefile b/Makefile
index 5e01a416c6e4..f8b921658f29 100644
--- a/Makefile
+++ b/Makefile
@@ -626,7 +626,11 @@ 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

2015-11-24 10:20:48

by Michal Marek

Subject: Re: [PATCH] Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES

On 2015-11-23 17:26, Arnd Bergmann wrote:
> 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.
[...]
> diff --git a/Makefile b/Makefile
> index 5e01a416c6e4..f8b921658f29 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -626,7 +626,11 @@ 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

Does it only happen with -O2? Normally, we would add it outside the
ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE.

Michal

2015-11-24 10:43:17

by Arnd Bergmann

Subject: Re: [PATCH] Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES

On Tuesday 24 November 2015 11:20:43 Michal Marek wrote:
> > diff --git a/Makefile b/Makefile
> > index 5e01a416c6e4..f8b921658f29 100644
> > --- a/Makefile
> > +++ b/Makefile
> > @@ -626,7 +626,11 @@ 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
>
> Does it only happen with -O2? Normally, we would add it outside the
> ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE.
>

We already disable the warning for -Os builds based on a patch we merged
a while ago. It seems easier to add it to the block we already have.

Arnd

2015-11-24 12:07:27

by Michal Marek

Subject: Re: [PATCH] Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES

On 2015-11-24 11:42, Arnd Bergmann wrote:
> On Tuesday 24 November 2015 11:20:43 Michal Marek wrote:
>>> diff --git a/Makefile b/Makefile
>>> index 5e01a416c6e4..f8b921658f29 100644
>>> --- a/Makefile
>>> +++ b/Makefile
>>> @@ -626,7 +626,11 @@ 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
>>
>> Does it only happen with -O2? Normally, we would add it outside the
>> ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE.
>>
>
> We already disable the warning for -Os builds based on a patch we merged
> a while ago. It seems easier to add it to the block we already have.

I'm blind, sorry.

Michal