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

[Onur <work@onurozkan.dev>]

On Sat, 13 Sep 2025 13:08:47 +0300
Onur Özkan <work@onurozkan.dev> 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 supports the same flags as other Rust build rules, so
> it can also be used with `CLIPPY=1` (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@kernel.org>
> Link:
> https://rust-for-linux.zulipchat.com/#narrow/channel/288089/topic/x/near/539103602
> Signed-off-by: Onur Özkan <work@onurozkan.dev> ---
>  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
> +	$(Q)$(MAKE) $(build)=rust $@
> +
>  # Testing target
>  PHONY += rusttest
>  rusttest: prepare
> diff --git a/rust/Makefile b/rust/Makefile
> index bfa915b0e588..c148ef4a8c08 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)) \
> +        $(RUSTC_OR_CLIPPY) $(rust_common_flags) \
> +                @$(objtree)/include/generated/rustc_cfg
> $(rustc_target_flags) \
> +                --crate-type $(if
> $(rustc_check_library_proc),proc-macro,rlib) \
> +                $(if $(rustc_check_library_proc),,--emit=metadata) \
> +                --out-dir $(objtree)/$(obj)/check
> -L$(objtree)/$(obj)/check \
> +                --crate-name $(if
> $(rustc_check_crate_name),$(rustc_check_crate_name), \
> +				$(subst rustcheck-,,$(subst
> rustchecklib-,,$@))) $< +
> +rustcheck: rustchecklib-build_error rustchecklib-ffi
> rustchecklib-macros \
> +	rustchecklib-compiler_builtins
> rustchecklib-pin_init_internal \
> +	rustchecklib-pin_init rustchecklib-bindings
> rustchecklib-uapi \
> +	rustchecklib-kernel
> +
> +rustchecklib-build_error: $(src)/build_error.rs FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-ffi: $(src)/ffi.rs FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-macros: private rustc_target_flags = --extern proc_macro
> +rustchecklib-macros: private rustc_check_library_proc = yes
> +rustchecklib-macros: $(src)/macros/lib.rs FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-compiler_builtins: private rustc_check_crate_name =
> compiler_builtins_kernel +rustchecklib-compiler_builtins:
> $(src)/compiler_builtins.rs FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-pin_init_internal: private rustc_target_flags = --cfg
> kernel \
> +	--extern proc_macro
> +rustchecklib-pin_init_internal: private rustc_check_library_proc =
> yes +rustchecklib-pin_init_internal:
> $(src)/pin-init/internal/src/lib.rs FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-pin_init: private rustc_target_flags = --extern
> pin_init_internal \
> +	--extern macros --cfg kernel
> +rustchecklib-pin_init: $(src)/pin-init/src/lib.rs
> rustchecklib-macros \
> +	rustchecklib-pin_init_internal FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-bindings: private rustc_target_flags = --extern ffi
> +rustchecklib-bindings: $(src)/bindings/lib.rs \
> +    $(obj)/bindings/bindings_generated.rs \
> +    $(obj)/bindings/bindings_helpers_generated.rs \
> +    rustchecklib-ffi FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +rustchecklib-uapi: private rustc_target_flags = --extern ffi
> +rustchecklib-uapi: $(src)/uapi/lib.rs $(obj)/uapi/uapi_generated.rs \
> +    rustchecklib-ffi FORCE
> +	+$(call if_changed,rustc_check_library)
> +
> +ifdef CONFIG_JUMP_LABEL
> +rustchecklib-kernel:
> $(obj)/kernel/generated_arch_static_branch_asm.rs FORCE +endif
> +ifndef CONFIG_UML
> +ifdef CONFIG_BUG
> +rustchecklib-kernel: $(obj)/kernel/generated_arch_warn_asm.rs \
> +	$(obj)/kernel/generated_arch_reachable_asm.rs FORCE
> +endif
> +endif
> +
> +rustchecklib-kernel: private rustc_target_flags = --extern ffi
> --extern pin_init \
> +	--extern build_error --extern macros --extern bindings
> --extern uapi +rustchecklib-kernel: $(src)/kernel/lib.rs
> rustchecklib-ffi rustchecklib-pin_init \
> +	rustchecklib-build_error rustchecklib-macros
> rustchecklib-bindings \
> +	rustchecklib-uapi FORCE
> +	+$(call if_changed,rustc_check_library)
> +
>  ifdef CONFIG_CC_IS_CLANG
>  bindgen_c_flags = $(c_flags)
>  else

Seems like I got some indentation issues, will handle in in the next
version after some feedbacks.

-Onur