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authorGustavo A. R. Silva <gustavoars@kernel.org>2021-11-13 18:57:25 -0600
committerLinus Torvalds <torvalds@linux-foundation.org>2021-11-14 13:27:30 -0800
commitdee2b702bcf067d7b6b62c18bdd060ff0810a800 (patch)
tree53daf07f8ded4a59038ee0265bcc3f094a6e43b8
parentce49bfc8d0372212ccd7d1c1b45c60b077f77684 (diff)
kconfig: Add support for -Wimplicit-fallthrough
Add Kconfig support for -Wimplicit-fallthrough for both GCC and Clang. The compiler option is under configuration CC_IMPLICIT_FALLTHROUGH, which is enabled by default. Special thanks to Nathan Chancellor who fixed the Clang bug[1][2]. This bugfix only appears in Clang 14.0.0, so older versions still contain the bug and -Wimplicit-fallthrough won't be enabled for them, for now. This concludes a long journey and now we are finally getting rid of the unintentional fallthrough bug-class in the kernel, entirely. :) Link: https://github.com/llvm/llvm-project/commit/9ed4a94d6451046a51ef393cd62f00710820a7e8 [1] Link: https://bugs.llvm.org/show_bug.cgi?id=51094 [2] Link: https://github.com/KSPP/linux/issues/115 Link: https://github.com/ClangBuiltLinux/linux/issues/236 Co-developed-by: Kees Cook <keescook@chromium.org> Signed-off-by: Kees Cook <keescook@chromium.org> Co-developed-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org> Reviewed-by: Nathan Chancellor <nathan@kernel.org> Tested-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--Makefile6
-rw-r--r--init/Kconfig5
2 files changed, 6 insertions, 5 deletions
diff --git a/Makefile b/Makefile
index d83d72c26aaa..9cf9d5c1ed8f 100644
--- a/Makefile
+++ b/Makefile
@@ -789,7 +789,7 @@ stackp-flags-$(CONFIG_STACKPROTECTOR_STRONG) := -fstack-protector-strong
KBUILD_CFLAGS += $(stackp-flags-y)
KBUILD_CFLAGS-$(CONFIG_WERROR) += -Werror
-KBUILD_CFLAGS += $(KBUILD_CFLAGS-y)
+KBUILD_CFLAGS += $(KBUILD_CFLAGS-y) $(CONFIG_CC_IMPLICIT_FALLTHROUGH)
ifdef CONFIG_CC_IS_CLANG
KBUILD_CPPFLAGS += -Qunused-arguments
@@ -801,10 +801,6 @@ KBUILD_CFLAGS += -Wno-gnu
KBUILD_CFLAGS += -mno-global-merge
else
-# Warn about unmarked fall-throughs in switch statement.
-# Disabled for clang while comment to attribute conversion happens and
-# https://github.com/ClangBuiltLinux/linux/issues/636 is discussed.
-KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough=5,)
# gcc inanely warns about local variables called 'main'
KBUILD_CFLAGS += -Wno-main
endif
diff --git a/init/Kconfig b/init/Kconfig
index 45bcaa8e7481..036b750e8d8a 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -885,6 +885,11 @@ config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
config CC_HAS_INT128
def_bool !$(cc-option,$(m64-flag) -D__SIZEOF_INT128__=0) && 64BIT
+config CC_IMPLICIT_FALLTHROUGH
+ string
+ default "-Wimplicit-fallthrough=5" if CC_IS_GCC
+ default "-Wimplicit-fallthrough" if CC_IS_CLANG && $(cc-option,-Wunreachable-code-fallthrough)
+
#
# For architectures that know their GCC __int128 support is sound
#