On Sat, Nov 13, 2021 at 06:57:25PM -0600, Gustavo A. R. Silva wrote: > 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. :) > > [1] https://github.com/llvm/llvm-project/commit/9ed4a94d6451046a51ef393cd62f00710820a7e8 > [2] https://bugs.llvm.org/show_bug.cgi?id=51094 > > Link: https://github.com/KSPP/linux/issues/115 > Link: https://github.com/ClangBuiltLinux/linux/issues/236 > Co-developed-by: Kees Cook <keescook@xxxxxxxxxxxx> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx> > Co-developed-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx> This appears to do the right thing with both clang-13 and clang-14. Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx> Tested-by: Nathan Chancellor <nathan@xxxxxxxxxx> It feels a little odd to have this in Kconfig but if it works and gets the warning enabled, then so be it. > --- > Makefile | 6 +----- > init/Kconfig | 5 +++++ > 2 files changed, 6 insertions(+), 5 deletions(-) > > diff --git a/Makefile b/Makefile > index 30c7c81d0437..f18a50daad00 100644 > --- a/Makefile > +++ b/Makefile > @@ -786,7 +786,7 @@ 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 > @@ -798,10 +798,6 @@ 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 += $(call cc-option,-Wimplicit-fallthrough=5,) > # gcc inanely warns about local variables called 'main' > KBUILD_CFLAGS += -Wno-main > endif > diff --git a/init/Kconfig b/init/Kconfig > index 11f8a845f259..b0582cd3e096 100644 > --- a/init/Kconfig > +++ b/init/Kconfig > @@ -885,6 +885,11 @@ config ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH > config CC_HAS_INT128 > def_bool !$(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 > # > -- > 2.27.0 > >
