From 1d87ce1ae1a7d4deb9bc81d9b9ccac3ab6633cf8 Mon Sep 17 00:00:00 2001 From: Masahiro Yamada Date: Thu, 21 Feb 2019 13:13:38 +0900 Subject: [PATCH] kbuild: compute false-positive -Wmaybe-uninitialized cases in Kconfig Since -Wmaybe-uninitialized was introduced by GCC 4.7, we have patched various false positives: - commit ca81ba750ad1 ("Turn off -Wmaybe-uninitialized when building with -Os") turned off this option for -Os. - commit 996f52f219a9 ("Kbuild: disable 'maybe-uninitialized' warning for CONFIG_PROFILE_ALL_BRANCHES") turned off this option for CONFIG_PROFILE_ALL_BRANCHES - commit 62915b141655 ("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 Reviewed-by: Nathan Chancellor Tested-by: Nick Desaulniers --- Makefile | 10 +++------- init/Kconfig | 17 +++++++++++++++++ kernel/trace/Kconfig | 1 + 3 files changed, 21 insertions(+), 7 deletions(-) diff --git a/Makefile b/Makefile index 7d9032bf47c5c..9f52fda4ad0e7 100644 --- a/Makefile +++ b/Makefile @@ -660,17 +660,13 @@ 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 513fa544a134c..ce43083b681dd 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 @@ -1102,6 +1118,7 @@ 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 fa8b1fe824f32..8bd1d6d001d7b 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. -- 2.39.5