Re: [PATCH v2 1/1] rust: add `rustcheck` make target for check-only builds

[Nicolas Schier]

On Mon, Sep 15, 2025 at 02:53:11PM +0300, Onur Özkan wrote:
> Adds a new `rustcheck` make target to run a check-only build
> similar to `cargo check`. This allows us to verify that the Rust
> sources can build without building/linking final artifacts,
> which speeds up the iteration (a lot) during development.
> 
> The target also supports the CLIPPY flag (e.g., `make LLVM=1
> rustcheck CLIPPY=1) to run Clippy in a faster way.
> 
> Also, unlike `make LLVM=1`, it doesn't compile large amounts of C
> code (on a fresh checkout) when the goal is only to check that
> Rust builds are not broken after some changes.
> 
> Suggested-by: Benno Losin <lossin@xxxxxxxxxx>
> Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089/topic/x/near/539103602
> Signed-off-by: Onur Özkan <work@xxxxxxxxxxxxx>
> ---
>  Makefile      |  7 +++++
>  rust/Makefile | 73 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 80 insertions(+)
> 
> diff --git a/Makefile b/Makefile
> index cf37b9407821..7812cdc72938 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1716,6 +1716,8 @@ help:
>  	@echo  '		    is formatted, printing a diff otherwise.'
>  	@echo  '  rustdoc	  - Generate Rust documentation'
>  	@echo  '		    (requires kernel .config)'
> +	@echo  '  rustcheck       - Check that the Rust code builds'
> +	@echo  '                    (requires kernel .config)'
>  	@echo  '  rusttest        - Runs the Rust tests'
>  	@echo  '                    (requires kernel .config; downloads external repos)'
>  	@echo  '  rust-analyzer	  - Generate rust-project.json rust-analyzer support file'
> @@ -1821,6 +1823,11 @@ PHONY += rustdoc
>  rustdoc: prepare
>  	$(Q)$(MAKE) $(build)=rust $@
>  
> +# Checking Rust sources.
> +PHONY += rustcheck
> +rustcheck: prepare0

Why do you let rustcheck depend on prepare0 instead of prepare?

> +	$(Q)$(MAKE) $(build)=rust $@
> +
>  # Testing target
>  PHONY += rusttest
>  rusttest: prepare
> diff --git a/rust/Makefile b/rust/Makefile
> index bfa915b0e588..b45878870207 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -265,6 +265,79 @@ rusttest-kernel: $(src)/kernel/lib.rs rusttestlib-ffi rusttestlib-kernel \
>      rusttestlib-uapi rusttestlib-pin_init FORCE
>  	+$(call if_changed,rustc_test)
>  
> +## Check-only compilation (similar to `cargo check`)
> +quiet_cmd_rustc_check_library = $(RUSTC_OR_CLIPPY_QUIET) CHECK $<
> +      cmd_rustc_check_library = \
> +        OBJTREE=$(abspath $(objtree)) \

Have you tried this?

        OBJTREE=$(CURDIR) \

or

        OBJTREE=$(abs_output) \

I'd favor using one of these instead.

Kind regards,
Nicolas

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