From: Masahiro Yamada yamada.masahiro@socionext.com
commit b303c6df80c9f8f13785aa83a0471fca7e38b24d upstream.
Since -Wmaybe-uninitialized was introduced by GCC 4.7, we have patched various false positives:
- commit e74fc973b6e5 ("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
--- Makefile | 11 ++++------- init/Kconfig | 17 +++++++++++++++++ kernel/trace/Kconfig | 1 + 3 files changed, 22 insertions(+), 7 deletions(-)
--- a/Makefile +++ b/Makefile @@ -658,17 +658,14 @@ KBUILD_CFLAGS += $(call cc-option,-fdata 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
# Tell gcc to never replace conditional load with a non-conditional one KBUILD_CFLAGS += $(call cc-option,--param=allow-store-data-races=0) --- a/init/Kconfig +++ b/init/Kconfig @@ -16,6 +16,22 @@ config DEFCONFIG_LIST default "$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 @@ -1333,6 +1349,7 @@ 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. --- a/kernel/trace/Kconfig +++ b/kernel/trace/Kconfig @@ -342,6 +342,7 @@ 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.