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>
diff --git a/init/Kconfig b/init/Kconfig
index 45bcaa8..036b750 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -885,6 +885,11 @@
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
#
