Re: [PATCH 2/3] kbuild: rust: apply `CONFIG_WERROR` to all Rust targets

Masahiro Yamada
2024-05-21T04:15:19Z

On Mon, May 20, 2024 at 6:12 AM Miguel Ojeda <ojeda@kernel.org> wrote:
>
> Make all Rust code (i.e. not just kernel code) respect `CONFIG_WERROR`,
> so that we keep everything warning clean.

Rust started to do something different from C.

KBUILD_HOSTCFLAGS is not affected by any CONFIG option.

The reason is because HOSTCC is needed for building Kconfig.
If the flags for HOSTCC is changed by a CONFIG option,
it would be a chicken-egg problem.
Also, some host programs might be compiled even
without .config at all. (e.g. scripts/unifdef)

I know Rust will not become a part of the core infrastructure
of the build system, but IMHO, host programs should not be
affected by any CONFIG option.

I do not like this patch.

>
> In particular, this affects targets in `rust/` (`RUSTDOC H`, `RUSTC TL`,
> `RUSTDOC T`, `RUSTC T` and `RUSTC P`), plus host programs and any others
> we may add later.
>
> Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
> ---
> This one requires the `rusttest` warning cleanup at
> https://lore.kernel.org/rust-for-linux/20240519210735.587323-1-ojeda@kernel.org/
>
> Makefile | 4 ++--
> scripts/Makefile.extrawarn | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/Makefile b/Makefile
> index fba567a55607..2d0ea441cb9c 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -469,7 +469,7 @@ export rust_common_flags := --edition=2021 \
>
> KBUILD_HOSTCFLAGS := $(KBUILD_USERHOSTCFLAGS) $(HOST_LFS_CFLAGS) $(HOSTCFLAGS)
> KBUILD_HOSTCXXFLAGS := -Wall -O2 $(HOST_LFS_CFLAGS) $(HOSTCXXFLAGS)
> -KBUILD_HOSTRUSTFLAGS := $(rust_common_flags) -O -Cstrip=debuginfo \
> +KBUILD_HOSTRUSTFLAGS = $(rust_common_flags) -O -Cstrip=debuginfo \
> -Zallow-features= $(HOSTRUSTFLAGS)
> KBUILD_HOSTLDFLAGS := $(HOST_LFS_LDFLAGS) $(HOSTLDFLAGS)
> KBUILD_HOSTLDLIBS := $(HOST_LFS_LIBS) $(HOSTLDLIBS)
> @@ -560,7 +560,7 @@ KBUILD_CFLAGS += -fno-PIE
> KBUILD_CFLAGS += -fno-strict-aliasing
>
> KBUILD_CPPFLAGS := -D__KERNEL__
> -KBUILD_RUSTFLAGS := $(rust_common_flags) \
> +KBUILD_RUSTFLAGS = $(rust_common_flags) \
> -Cpanic=abort -Cembed-bitcode=n -Clto=n \
> -Cforce-unwind-tables=n -Ccodegen-units=1 \
> -Csymbol-mangling-version=v0 \
> diff --git a/scripts/Makefile.extrawarn b/scripts/Makefile.extrawarn
> index 48114e91c386..990890821889 100644
> --- a/scripts/Makefile.extrawarn
> +++ b/scripts/Makefile.extrawarn
> @@ -26,8 +26,8 @@ endif
>
> KBUILD_CPPFLAGS-$(CONFIG_WERROR) += -Werror
> KBUILD_CPPFLAGS += $(KBUILD_CPPFLAGS-y)
> -KBUILD_RUSTFLAGS-$(CONFIG_WERROR) += -Dwarnings
> -KBUILD_RUSTFLAGS += $(KBUILD_RUSTFLAGS-y)
> +rust_common_flags-$(CONFIG_WERROR) += -Dwarnings
> +rust_common_flags += $(rust_common_flags-y)
>
> KBUILD_CFLAGS-$(CONFIG_CC_NO_ARRAY_BOUNDS) += -Wno-array-bounds
>
> --
> 2.45.1

--
Best Regards

Masahiro Yamada