On Wed, Feb 20, 2019 at 8:14 PM Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> wrote: > > 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. > > Signed-off-by: Masahiro Yamada <yamada.masahiro@xxxxxxxxxxxxx> I verified that mainline+this patch did not regression arm64 allyesconfig clang build. Tested-by: Nick Desaulniers <ndesaulniers@xxxxxxxxxx> Thanks for the patch! Would you mind adding a link tag to: Link: https://github.com/ClangBuiltLinux/linux/issues/350 > --- > > Makefile | 10 +++------- > init/Kconfig | 17 +++++++++++++++++ > kernel/trace/Kconfig | 1 + > 3 files changed, 21 insertions(+), 7 deletions(-) > > diff --git a/Makefile b/Makefile > index 1bb0535..b21aa2e3 100644 > --- a/Makefile > +++ b/Makefile > @@ -656,17 +656,13 @@ KBUILD_CFLAGS += $(call cc-disable-warning, int-in-bool-context) > > ifdef CONFIG_CC_OPTIMIZE_FOR_SIZE > KBUILD_CFLAGS += $(call cc-option,-Oz,-Os) > -KBUILD_CFLAGS += $(call cc-disable-warning,maybe-uninitialized,) > -else > -ifdef CONFIG_PROFILE_ALL_BRANCHES > -KBUILD_CFLAGS += -O2 $(call cc-disable-warning,maybe-uninitialized,) > 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) > diff --git a/init/Kconfig b/init/Kconfig > index c9386a3..1f05a88 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -26,6 +26,22 @@ config CLANG_VERSION > config CC_HAS_ASM_GOTO > def_bool $(success,$(srctree)/scripts/gcc-goto.sh $(CC)) > > +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 > @@ -1113,6 +1129,7 @@ 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. > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig > index fa8b1fe..8bd1d6d 100644 > --- a/kernel/trace/Kconfig > +++ b/kernel/trace/Kconfig > @@ -370,6 +370,7 @@ config PROFILE_ANNOTATED_BRANCHES > config PROFILE_ALL_BRANCHES > bool "Profile all if conditionals" if !FORTIFY_SOURCE > 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. > -- > 2.7.4 > -- Thanks, ~Nick Desaulniers