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

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commit b303c6df80 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 815eb71e71 ("Kbuild: disable 'maybe-uninitialized' warning
   for CONFIG_PROFILE_ALL_BRANCHES") turned off this option for
   CONFIG_PROFILE_ALL_BRANCHES

 - commit a76bcf557e ("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 Chris
parent a72aa85d8b
commit ba3c68463a
3 changed files with 22 additions and 7 deletions
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11
Makefile
View File

@@ -728,17 +728,14 @@ export DISABLE_CFI
endif
ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE
KBUILD_CFLAGS += -Os $(call cc-disable-warning,maybe-uninitialized,)
else
ifdef CONFIG_PROFILE_ALL_BRANCHES
KBUILD_CFLAGS += -O2 $(call cc-disable-warning,maybe-uninitialized,)
KBUILD_CFLAGS += -Os
else
KBUILD_CFLAGS += -O2
endif
endif
KBUILD_CFLAGS += $(call cc-ifversion, -lt, 0409, \
$(call cc-disable-warning,maybe-uninitialized,))
ifdef CONFIG_CC_DISABLE_WARN_MAYBE_UNINITIALIZED
KBUILD_CFLAGS += -Wno-maybe-uninitialized
endif
ifdef CONFIG_CC_WERROR
KBUILD_CFLAGS += -Werror

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
@@ -1472,6 +1488,7 @@ 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

@@ -356,6 +356,7 @@ 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.