linux-kernel - Re: [PATCH 4/6] kbuild: rust: rebuild if the version text changes

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Message-ID: <20240817-cute-doberman-from-shambhala-6f42db@lindesnes>
Date: Sat, 17 Aug 2024 15:04:39 +0200
From: Nicolas Schier <nicolas@...sle.eu>
To: Miguel Ojeda <ojeda@...nel.org>
Cc: Alex Gaynor <alex.gaynor@...il.com>,
	Wedson Almeida Filho <wedsonaf@...il.com>,
	Masahiro Yamada <masahiroy@...nel.org>,
	Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
	Björn Roy Baron <bjorn3_gh@...tonmail.com>,
	Benno Lossin <benno.lossin@...ton.me>,
	Andreas Hindborg <a.hindborg@...sung.com>,
	Alice Ryhl <aliceryhl@...gle.com>, rust-for-linux@...r.kernel.org,
	Nathan Chancellor <nathan@...nel.org>, linux-kbuild@...r.kernel.org,
	linux-kernel@...r.kernel.org, patches@...ts.linux.dev
Subject: Re: [PATCH 4/6] kbuild: rust: rebuild if the version text changes

On Fri, Aug 09, 2024 at 12:11:36AM +0200, Miguel Ojeda wrote:
> Now that `RUSTC_VERSION_TEXT` exists, use it to rebuild `core` when the
> version text changes (which in turn will trigger a rebuild of all the
> kernel Rust code).
> 
> This also applies to proc macros (which only work with the `rustc` that
> compiled them), via the already existing dependency on `core.o`. That
> is cleaned up in the next commit.
> 
> However, this does not cover host programs written in Rust, which is
> the same case in the C side.
> 
> This is accomplished by referencing directly the generated file, instead
> of using the `fixdep` header trick, since we cannot change the Rust
> standard library sources. This is not too much of a burden, since it
> only needs to be done for `core`.
> 
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
> Masahiro: I used `$(objtree)` here since we still use it in the rest of
> this `Makefile`, but please let me know if you prefer otherwise. Thanks!
> 
>  rust/Makefile | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/rust/Makefile b/rust/Makefile
> index 6c0644b6090c..966743a9ee25 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -370,7 +370,8 @@ $(obj)/core.o: private skip_clippy = 1
>  $(obj)/core.o: private skip_flags = -Wunreachable_pub
>  $(obj)/core.o: private rustc_objcopy = $(foreach sym,$(redirect-intrinsics),--redefine-sym $(sym)=__rust$(sym))
>  $(obj)/core.o: private rustc_target_flags = $(core-cfgs)
> -$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs FORCE
> +$(obj)/core.o: $(RUST_LIB_SRC)/core/src/lib.rs \
> +    $(wildcard $(objtree)/include/config/RUSTC_VERSION_TEXT) FORCE
>  	+$(call if_changed_dep,rustc_library)
>  ifneq ($(or $(CONFIG_X86_64),$(CONFIG_X86_32)),)
>  $(obj)/core.o: scripts/target.json
> --
> 2.46.0

Looks good to me, but I'd prefer something like the suggestion from
Masahiro:
https://lore.kernel.org/linux-kbuild/CAK7LNAQBG0nDupXSgAAk-6nOqeqGVkr3H1RjYaqRJ1OxmLm6xA@mail.gmail.com/