| Message ID | 20190815182029.197604-1-nhuck@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: Require W=1 for -Wimplicit-fallthrough with clang | expand |
On Thu, Aug 15, 2019 at 11:20:29AM -0700, 'Nathan Huckleberry' via Clang Built Linux wrote: > Clang is updating to support -Wimplicit-fallthrough on C > https://reviews.llvm.org/D64838. Since clang does not > support the comment version of fallthrough annotations > this update causes an additional 50k warnings. Most > of these warnings (>49k) are duplicates from header files. > > This patch is intended to be reverted after the warnings > have been cleaned up. > > Signed-off-by: Nathan Huckleberry <nhuck@google.com> > --- > Makefile | 4 ++++ > scripts/Makefile.extrawarn | 3 +++ > 2 files changed, 7 insertions(+) > > diff --git a/Makefile b/Makefile > index 1b23f95db176..93b9744e66a2 100644 > --- a/Makefile > +++ b/Makefile > @@ -846,7 +846,11 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > KBUILD_CFLAGS += -Wdeclaration-after-statement > > # Warn about unmarked fall-throughs in switch statement. > +# If the compiler is clang, this warning is only enabled if W=1 in > +# Makefile.extrawarn > +ifndef CONFIG_CC_IS_CLANG > KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) > +endif > > # Variable Length Arrays (VLAs) should not be used anywhere in the kernel > KBUILD_CFLAGS += -Wvla > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn > index a74ce2e3c33e..e12359d69bb7 100644 > --- a/scripts/Makefile.extrawarn > +++ b/scripts/Makefile.extrawarn > @@ -30,6 +30,9 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable) > warning-1 += $(call cc-option, -Wunused-const-variable) > warning-1 += $(call cc-option, -Wpacked-not-aligned) > warning-1 += $(call cc-option, -Wstringop-truncation) > +ifdef CONFIG_CC_IS_CLANG > +KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) Shouldn't this be warning-1? > +endif > # The following turn off the warnings enabled by -Wextra > warning-1 += -Wno-missing-field-initializers > warning-1 += -Wno-sign-compare > -- > 2.23.0.rc1.153.gdeed80330f-goog > I am still not a huge fan of the CONFIG_CC_IS_CLANG ifdefs but I don't really see a much cleaner way to get around this. Some that come to mind: * Leave Makefile alone and add KBUILD_CFLAGS += -Wno-implicit-fallthrough in the CONFIG_CC_IS_CLANG section of scripts/Makefile.extrawarn * Revert commit bfd77145f35c ("Makefile: Convert -Wimplicit-fallthrough=3 to just -Wimplicit-fallthrough for clang") for the time being and just rely on adding -Wimplicit-fallthrough to KCFLAGS for testing. Regardless: Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
On Thu, Aug 15, 2019 at 1:45 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > On Thu, Aug 15, 2019 at 11:20:29AM -0700, 'Nathan Huckleberry' via Clang Built Linux wrote: > > Clang is updating to support -Wimplicit-fallthrough on C > > https://reviews.llvm.org/D64838. Since clang does not > > support the comment version of fallthrough annotations > > this update causes an additional 50k warnings. Most > > of these warnings (>49k) are duplicates from header files. > > > > This patch is intended to be reverted after the warnings > > have been cleaned up. > > > > Signed-off-by: Nathan Huckleberry <nhuck@google.com> > > --- > > Makefile | 4 ++++ > > scripts/Makefile.extrawarn | 3 +++ > > 2 files changed, 7 insertions(+) > > > > diff --git a/Makefile b/Makefile > > index 1b23f95db176..93b9744e66a2 100644 > > --- a/Makefile > > +++ b/Makefile > > @@ -846,7 +846,11 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) > > KBUILD_CFLAGS += -Wdeclaration-after-statement > > > > # Warn about unmarked fall-throughs in switch statement. > > +# If the compiler is clang, this warning is only enabled if W=1 in > > +# Makefile.extrawarn > > +ifndef CONFIG_CC_IS_CLANG > > KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) > > +endif > > > > # Variable Length Arrays (VLAs) should not be used anywhere in the kernel > > KBUILD_CFLAGS += -Wvla > > diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn > > index a74ce2e3c33e..e12359d69bb7 100644 > > --- a/scripts/Makefile.extrawarn > > +++ b/scripts/Makefile.extrawarn > > @@ -30,6 +30,9 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable) > > warning-1 += $(call cc-option, -Wunused-const-variable) > > warning-1 += $(call cc-option, -Wpacked-not-aligned) > > warning-1 += $(call cc-option, -Wstringop-truncation) > > +ifdef CONFIG_CC_IS_CLANG > > +KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) > > Shouldn't this be warning-1? +1 > > > +endif > > # The following turn off the warnings enabled by -Wextra > > warning-1 += -Wno-missing-field-initializers > > warning-1 += -Wno-sign-compare > > -- > > 2.23.0.rc1.153.gdeed80330f-goog > > > > I am still not a huge fan of the CONFIG_CC_IS_CLANG ifdefs but I don't > really see a much cleaner way to get around this. Some that come to > mind: > > * Leave Makefile alone and add > > KBUILD_CFLAGS += -Wno-implicit-fallthrough > > in the CONFIG_CC_IS_CLANG section of scripts/Makefile.extrawarn Yeah, I think this might be cleaner. -Wimplicit-fallthrough -Wno-implicit-fallthrough will be passed to Clang, but "last one wins." A smaller patch makes it more likely to be revertable without potentially having to resolve any conflicts. Would you mind sending a V2 with that change? You can include Nathan's Suggested-by tag.
On Thu, Aug 15, 2019 at 10:45 PM Nathan Chancellor <natechancellor@gmail.com> wrote: > > I am still not a huge fan of the CONFIG_CC_IS_CLANG ifdefs but I don't > really see a much cleaner way to get around this. Some that come to > mind: Yeah... > * Revert commit bfd77145f35c ("Makefile: Convert -Wimplicit-fallthrough=3 > to just -Wimplicit-fallthrough for clang") for the time being and just > rely on adding -Wimplicit-fallthrough to KCFLAGS for testing. I would avoid applying commits that will have to be reverted just for Clang, particularly since it is not fully supported yet. Cheers, Miguel
On Thu, Aug 15, 2019 at 3:59 PM Miguel Ojeda <miguel.ojeda.sandonis@gmail.com> wrote: > > On Thu, Aug 15, 2019 at 10:45 PM Nathan Chancellor > <natechancellor@gmail.com> wrote: > > * Revert commit bfd77145f35c ("Makefile: Convert -Wimplicit-fallthrough=3 > > to just -Wimplicit-fallthrough for clang") for the time being and just > > rely on adding -Wimplicit-fallthrough to KCFLAGS for testing. > > I would avoid applying commits that will have to be reverted just for > Clang, particularly since it is not fully supported yet. "not fully supported yet" you say? *drops monocle* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS?h=v5.3-rc4#n4001
On Fri, Aug 16, 2019 at 1:05 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Aug 15, 2019 at 3:59 PM Miguel Ojeda > <miguel.ojeda.sandonis@gmail.com> wrote: > > > > On Thu, Aug 15, 2019 at 10:45 PM Nathan Chancellor > > <natechancellor@gmail.com> wrote: > > > * Revert commit bfd77145f35c ("Makefile: Convert -Wimplicit-fallthrough=3 > > > to just -Wimplicit-fallthrough for clang") for the time being and just > > > rely on adding -Wimplicit-fallthrough to KCFLAGS for testing. > > > > I would avoid applying commits that will have to be reverted just for > > Clang, particularly since it is not fully supported yet. > > "not fully supported yet" you say? *drops monocle* > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/MAINTAINERS?h=v5.3-rc4#n4001 By fully supported I mean it already works and people can rely on it out of the box using a released version of Clang/LLVM. Is that the case already? If so, many places need updating! * include/linux/compiler-clang.h should check for the minimum supported version * Documentation/process/programming-language.rst should be updated * https://github.com/ClangBuiltLinux/linux/wiki does not mention anything etc. Cheers, Miguel
diff --git a/Makefile b/Makefile index 1b23f95db176..93b9744e66a2 100644 --- a/Makefile +++ b/Makefile @@ -846,7 +846,11 @@ NOSTDINC_FLAGS += -nostdinc -isystem $(shell $(CC) -print-file-name=include) KBUILD_CFLAGS += -Wdeclaration-after-statement # Warn about unmarked fall-throughs in switch statement. +# If the compiler is clang, this warning is only enabled if W=1 in +# Makefile.extrawarn +ifndef CONFIG_CC_IS_CLANG KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) +endif # Variable Length Arrays (VLAs) should not be used anywhere in the kernel KBUILD_CFLAGS += -Wvla diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn index a74ce2e3c33e..e12359d69bb7 100644 --- a/scripts/Makefile.extrawarn +++ b/scripts/Makefile.extrawarn @@ -30,6 +30,9 @@ warning-1 += $(call cc-option, -Wunused-but-set-variable) warning-1 += $(call cc-option, -Wunused-const-variable) warning-1 += $(call cc-option, -Wpacked-not-aligned) warning-1 += $(call cc-option, -Wstringop-truncation) +ifdef CONFIG_CC_IS_CLANG +KBUILD_CFLAGS += $(call cc-option,-Wimplicit-fallthrough,) +endif # The following turn off the warnings enabled by -Wextra warning-1 += -Wno-missing-field-initializers warning-1 += -Wno-sign-compare
Clang is updating to support -Wimplicit-fallthrough on C https://reviews.llvm.org/D64838. Since clang does not support the comment version of fallthrough annotations this update causes an additional 50k warnings. Most of these warnings (>49k) are duplicates from header files. This patch is intended to be reverted after the warnings have been cleaned up. Signed-off-by: Nathan Huckleberry <nhuck@google.com> --- Makefile | 4 ++++ scripts/Makefile.extrawarn | 3 +++ 2 files changed, 7 insertions(+)