* [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS
@ 2019-06-11 18:43 Nathan Chancellor
2019-06-11 19:37 ` Nick Desaulniers
2019-06-20 14:23 ` Masahiro Yamada
0 siblings, 2 replies; 3+ messages in thread
From: Nathan Chancellor @ 2019-06-11 18:43 UTC (permalink / raw)
To: Masahiro Yamada, Michal Marek, linux-kbuild, linux-kernel
Cc: clang-built-linux, Nick Desaulniers, Nathan Chancellor, Peter Smith
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(+)
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 += $(CLANG_FLAGS)
export CLANG_FLAGS
--
2.22.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS
2019-06-11 18:43 [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS Nathan Chancellor
@ 2019-06-11 19:37 ` Nick Desaulniers
2019-06-20 14:23 ` Masahiro Yamada
1 sibling, 0 replies; 3+ messages in thread
From: Nick Desaulniers @ 2019-06-11 19:37 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Masahiro Yamada, Michal Marek, Linux Kbuild mailing list, LKML,
clang-built-linux, Peter Smith
On Tue, Jun 11, 2019 at 11:43 AM Nathan Chancellor
<natechancellor@gmail.com> wrote:
> Suggested-by: Peter Smith <peter.smith@linaro.org>
> Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
I verified this has no negative effect with -Qunused-arguments and the
relative position of the two flags. The build failure is much more
explicit with this patch:
> error: unknown warning option '-Wno-psabi' [-Werror,-Wunknown-warning-option]
Tested-by: Nick Desaulniers <ndesaulniers@google.com>
> ---
> Makefile | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/Makefile b/Makefile
> index b81e17261250..5f9d09bd2252 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -528,6 +528,7 @@ ifneq ($(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
>
--
Thanks,
~Nick Desaulniers
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS
2019-06-11 18:43 [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS Nathan Chancellor
2019-06-11 19:37 ` Nick Desaulniers
@ 2019-06-20 14:23 ` Masahiro Yamada
1 sibling, 0 replies; 3+ messages in thread
From: Masahiro Yamada @ 2019-06-20 14:23 UTC (permalink / raw)
To: Nathan Chancellor
Cc: Michal Marek, Linux Kbuild mailing list,
Linux Kernel Mailing List, clang-built-linux, Nick Desaulniers,
Peter Smith
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!
--
Best Regards
Masahiro Yamada
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2019-06-20 14:24 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-06-11 18:43 [PATCH] kbuild: Add -Werror=unknown-warning-option to CLANG_FLAGS Nathan Chancellor
2019-06-11 19:37 ` Nick Desaulniers
2019-06-20 14:23 ` Masahiro Yamada
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).