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kbuild: compute false-positive -Wmaybe-uninitialized cases in Kconfig

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commit b303c6df80c9f8f13785aa83a0471fca7e38b24d upstream.

Since -Wmaybe-uninitialized was introduced by GCC 4.7, we have patched
various false positives:

 - commit e74fc973b6 ("Turn off -Wmaybe-uninitialized when building
   with -Os") turned off this option for -Os.

 - commit 815eb71e7149 ("Kbuild: disable 'maybe-uninitialized' warning
   for CONFIG_PROFILE_ALL_BRANCHES") turned off this option for
   CONFIG_PROFILE_ALL_BRANCHES

 - commit a76bcf557ef4 ("Kbuild: enable -Wmaybe-uninitialized warning
   for "make W=1"") turned off this option for GCC < 4.9
   Arnd provided more explanation in https://lkml.org/lkml/2017/3/14/903

I think this looks better by shifting the logic from Makefile to Kconfig.

Link: https://github.com/ClangBuiltLinux/linux/issues/350
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Masahiro Yamada 2019-02-21 13:13:38 +09:00 • committed by Greg Kroah-Hartman
parent bd395069dd
commit c50c2c2ed6
3 changed files with 22 additions and 1 deletions
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5
Makefile
View file

@ -631,7 +631,6 @@ ARCH_CFLAGS :=
include arch/$(SRCARCH)/Makefile
KBUILD_CFLAGS += $(call cc-option,-fno-delete-null-pointer-checks,)
KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,)
KBUILD_CFLAGS += $(call cc-disable-warning,frame-address,)
KBUILD_CFLAGS += $(call cc-disable-warning, format-truncation)
KBUILD_CFLAGS += $(call cc-disable-warning, format-overflow)
@ -649,6 +648,10 @@ KBUILD_CFLAGS += -O2
endif
endif
ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED
KBUILD_CFLAGS += -Wno-maybe-uninitialized
endif
# Tell gcc to never replace conditional load with a non-conditional one
KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0)

17
init/Kconfig
View file

@ -16,6 +16,22 @@ config DEFCONFIG_LIST
default "$ARCH_DEFCONFIG"
default "arch/$ARCH/defconfig"
config CC_HAS_WARN_MAYBE_UNINITIALIZED
def_bool $(cc-option,-Wmaybe-uninitialized)
help
GCC >= 4.7 supports this option.
config CC_DISABLE_WARN_MAYBE_UNINITIALIZED
bool
depends on CC_HAS_WARN_MAYBE_UNINITIALIZED
default CC_IS_GCC && GCC_VERSION < 40900 # unreliable for GCC < 4.9
help
GCC's -Wmaybe-uninitialized is not reliable by definition.
Lots of false positive warnings are produced in some cases.
If this option is enabled, -Wno-maybe-uninitialzed is passed
to the compiler to suppress maybe-uninitialized warnings.
config CONSTRUCTORS
bool
depends on !UML
@ -1331,6 +1347,7 @@ config CC_OPTIMIZE_FOR_PERFORMANCE
config CC_OPTIMIZE_FOR_SIZE
bool "Optimize for size"
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
Enabling this option will pass "-Os" instead of "-O2" to
your compiler resulting in a smaller kernel.

1
kernel/trace/Kconfig
View file

@ -312,6 +312,7 @@ config PROFILE_ANNOTATED_BRANCHES
config PROFILE_ALL_BRANCHES
bool "Profile all if conditionals"
select TRACE_BRANCH_PROFILING
imply CC_DISABLE_WARN_MAYBE_UNINITIALIZED # avoid false positives
help
This tracer profiles all branch conditions. Every if ()
taken in the kernel is recorded whether it hit or miss.