Skip to contentSkip to conversation

Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES

PATCH In review Arnd Bergmann 2 participants 4 messages Nov 23, 2015 – Nov 24, 2015

Subsystems (2)
Kbuild Generic include/asm header files
lore
Share & tools
lore

Arnd Bergmann

author maintainer
#0 lore raw

PATCH 1/1 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]>
Makefile +5 -1
index 5e01a416c6e4..f8b921658f29 100644
@@ -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
#1 lore raw
Quoted 3 lines · Arnd Bergmann

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.

[...]

Quoted 5 lines
Makefile +0 -0
index 5e01a416c6e4..f8b921658f29 100644

Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) · line 633

Quoted 9 lines
Makefile +5 -1
@@ -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

author maintainer
#2 lore raw
Quoted 9 lines · On Tuesday 24 November 2015 11:20:43 Michal Marek wrote:
Quoted 9 lines
Makefile +0 -1
index 5e01a416c6e4..f8b921658f29 100644
@@ -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
Quoted 9 lines

Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) · line 633

Quoted 5 lines
Makefile +5 -0
+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

#3 lore raw
Quoted 20 lines · Arnd Bergmann
Quoted 9 lines · On Tuesday 24 November 2015 11:20:43 Michal Marek wrote:
Quoted 9 lines
Makefile +0 -1
index 5e01a416c6e4..f8b921658f29 100644
@@ -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
Quoted 9 lines

Makefile KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,) · line 633

Quoted 5 lines
Makefile +5 -0
+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.

Quoted 2 lines

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