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 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>
diff --git a/init/Kconfig b/init/Kconfig
index 513fa54..ce43083 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -26,6 +26,22 @@
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_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.