| Message ID | 20190611184331.44242-1-natechancellor@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS | expand |
On Tue, Jun 11, 2019 at 11:43 AM Nathan Chancellor <natechancellor@gmail.com> wrote: > Suggested-by: Peter Smith <peter.smith@linaro.org> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> I verified this has no negative effect with -Qunused-arguments and the relative position of the two flags. The build failure is much more explicit with this patch: > error: unknown warning option '-Wno-psabi' [-Werror,-Wunknown-warning-option] Tested-by: Nick Desaulniers <ndesaulniers@google.com> > --- > Makefile | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/Makefile b/Makefile > index b81e17261250..5f9d09bd2252 100644 > --- a/Makefile > +++ b/Makefile > @@ -528,6 +528,7 @@ ifneq ($(GCC_TOOLCHAIN),) > CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN) > endif > CLANG_FLAGS += -no-integrated-as > +CLANG_FLAGS += -Werror=unknown-warning-option > KBUILD_CFLAGS += $(CLANG_FLAGS) > KBUILD_AFLAGS += $(CLANG_FLAGS) > export CLANG_FLAGS > -- > 2.22.0 >
On Wed, Jun 12, 2019 at 3:43 AM Nathan Chancellor <natechancellor@gmail.com> wrote: > > In commit ebcc5928c5d9 ("arm64: Silence gcc warnings about arch ABI > drift"), the arm64 Makefile added -Wno-psabi to KBUILD_CFLAGS, which is > a GCC only option so clang rightfully complains: > > warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] > > https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-warning-option > > However, by default, this is merely a warning so the build happily goes > on with a slew of these warnings in the process. > > Commit c3f0d0bc5b01 ("kbuild, LLVMLinux: Add -Werror to cc-option to > support clang") worked around this behavior in cc-option by adding > -Werror so that unknown flags cause an error. However, this all happens > silently and when an unknown flag is added to the build unconditionally > like -Wno-psabi, cc-option will always fail because there is always an > unknown flag in the list of flags. This manifested as link time failures > in the arm64 libstub because -fno-stack-protector didn't get added to > KBUILD_CFLAGS. > > To avoid these weird cryptic failures in the future, make clang behave > like gcc and immediately error when it encounters an unknown flag by > adding -Werror=unknown-warning-option to CLANG_FLAGS. This can be added > unconditionally for clang because it is supported by at least 3.0.0, > according to godbolt [1] and 4.0.0, according to its documentation [2], > which is far earlier than we typically support. > > [1]: https://godbolt.org/z/7F7rm3 > [2]: https://releases.llvm.org/4.0.0/tools/clang/docs/DiagnosticsReference.html#wunknown-warning-option > > Link: https://github.com/ClangBuiltLinux/linux/issues/511 > Link: https://github.com/ClangBuiltLinux/linux/issues/517 > Suggested-by: Peter Smith <peter.smith@linaro.org> > Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> > --- Applied to linux-kbuild. Thanks!
diff --git a/Makefile b/Makefile index b81e17261250..5f9d09bd2252 100644 --- a/Makefile +++ b/Makefile @@ -528,6 +528,7 @@ ifneq ($(GCC_TOOLCHAIN),) CLANG_FLAGS += --gcc-toolchain=$(GCC_TOOLCHAIN) endif CLANG_FLAGS += -no-integrated-as +CLANG_FLAGS += -Werror=unknown-warning-option KBUILD_CFLAGS += $(CLANG_FLAGS) KBUILD_AFLAGS += $(CLANG_FLAGS) export CLANG_FLAGS
In commit ebcc5928c5d9 ("arm64: Silence gcc warnings about arch ABI drift"), the arm64 Makefile added -Wno-psabi to KBUILD_CFLAGS, which is a GCC only option so clang rightfully complains: warning: unknown warning option '-Wno-psabi' [-Wunknown-warning-option] https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-warning-option However, by default, this is merely a warning so the build happily goes on with a slew of these warnings in the process. Commit c3f0d0bc5b01 ("kbuild, LLVMLinux: Add -Werror to cc-option to support clang") worked around this behavior in cc-option by adding -Werror so that unknown flags cause an error. However, this all happens silently and when an unknown flag is added to the build unconditionally like -Wno-psabi, cc-option will always fail because there is always an unknown flag in the list of flags. This manifested as link time failures in the arm64 libstub because -fno-stack-protector didn't get added to KBUILD_CFLAGS. To avoid these weird cryptic failures in the future, make clang behave like gcc and immediately error when it encounters an unknown flag by adding -Werror=unknown-warning-option to CLANG_FLAGS. This can be added unconditionally for clang because it is supported by at least 3.0.0, according to godbolt [1] and 4.0.0, according to its documentation [2], which is far earlier than we typically support. [1]: https://godbolt.org/z/7F7rm3 [2]: https://releases.llvm.org/4.0.0/tools/clang/docs/DiagnosticsReference.html#wunknown-warning-option Link: https://github.com/ClangBuiltLinux/linux/issues/511 Link: https://github.com/ClangBuiltLinux/linux/issues/517 Suggested-by: Peter Smith <peter.smith@linaro.org> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com> --- Makefile | 1 + 1 file changed, 1 insertion(+)