lkml.org 
[lkml]   [2019]   [Jul]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3] kbuild: Check for unknown options with cc-option usage in Kconfig and clang
On Tue, Jul 30, 2019 at 09:48:03AM -0700, Stephen Boyd wrote:
> If the particular version of clang a user has doesn't enable
> -Werror=unknown-warning-option by default, even though it is the
> default[1], then make sure to pass the option to the Kconfig cc-option
> command so that testing options from Kconfig files works properly.
> Otherwise, depending on the default values setup in the clang toolchain
> we will silently assume options such as -Wmaybe-uninitialized are
> supported by clang, when they really aren't.
>
> A compilation issue only started happening for me once commit
> 589834b3a009 ("kbuild: Add -Werror=unknown-warning-option to
> CLANG_FLAGS") was applied on top of commit b303c6df80c9 ("kbuild:
> compute false-positive -Wmaybe-uninitialized cases in Kconfig"). This
> leads kbuild to try and test for the existence of the
> -Wmaybe-uninitialized flag with the cc-option command in
> scripts/Kconfig.include, and it doesn't see an error returned from the
> option test so it sets the config value to Y. Then the Makefile tries to
> pass the unknown option on the command line and
> -Werror=unknown-warning-option catches the invalid option and breaks the
> build. Before commit 589834b3a009 ("kbuild: Add
> -Werror=unknown-warning-option to CLANG_FLAGS") the build works fine,
> but any cc-option test of a warning option in Kconfig files silently
> evaluates to true, even if the warning option flag isn't supported on
> clang.
>
> Note: This doesn't change cc-option usages in Makefiles because those
> use a different rule that includes KBUILD_CFLAGS by default (see the
> __cc-option command in scripts/Kbuild.incluide). The KBUILD_CFLAGS
> variable already has the -Werror=unknown-warning-option flag set. Thanks
> to Doug for pointing out the different rule.
>
> [1] https://clang.llvm.org/docs/DiagnosticsReference.html#wunknown-warning-option
> Cc: Peter Smith <peter.smith@linaro.org>
> Cc: Nathan Chancellor <natechancellor@gmail.com>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Cc: Douglas Anderson <dianders@chromium.org>
> Signed-off-by: Stephen Boyd <swboyd@chromium.org>

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>

> ---
> Makefile | 1 +
> scripts/Kconfig.include | 2 +-
> 2 files changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/Makefile b/Makefile
> index 9be5834073f8..517d0a3f6539 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -536,6 +536,7 @@ KBUILD_AFLAGS += $(CLANG_FLAGS)
> export CLANG_FLAGS
> endif
>
> +

Not sure it's worth sending a v4 for but I don't think this should be
there.

\
 
 \ /
  Last update: 2019-07-30 18:51    [W:0.058 / U:0.052 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site