Skip to content

Commit

Permalink
kconfig: Add support for -Wimplicit-fallthrough
Browse files Browse the repository at this point in the history
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: llvm/llvm-project@9ed4a94 [1]
Link: https://bugs.llvm.org/show_bug.cgi?id=51094 [2]
Link: KSPP#115
Link: ClangBuiltLinux#236
Co-developed-by: Kees Cook <[email protected]>
Signed-off-by: Kees Cook <[email protected]>
Co-developed-by: Linus Torvalds <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
Signed-off-by: Gustavo A. R. Silva <[email protected]>
Reviewed-by: Nathan Chancellor <[email protected]>
Tested-by: Nathan Chancellor <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
  • Loading branch information
GustavoARSilva authored and torvalds committed Nov 14, 2021
1 parent ce49bfc commit dee2b70
Show file tree
Hide file tree
Showing 2 changed files with 6 additions and 5 deletions.
6 changes: 1 addition & 5 deletions Makefile
Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand All @@ -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 += $(call cc-option,-Wimplicit-fallthrough=5,)
# gcc inanely warns about local variables called 'main'
KBUILD_CFLAGS += -Wno-main
endif
Expand Down
5 changes: 5 additions & 0 deletions init/Kconfig
Original file line number Diff line number Diff line change
Expand Up @@ -885,6 +885,11 @@ config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH
config CC_HAS_INT128
def_bool !$(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
#
Expand Down

0 comments on commit dee2b70

Please sign in to comment.