Re: [PATCH] rust: kbuild: Replace and dissolve procmacro-extension variable

[Tamir Duberstein]

On Tue, Jun 16, 2026 at 7:26 AM Nicolas Schier <n.schier@xxxxxxxxx> wrote:
>
> Use make's $(suffix) function [1] and substitution reference [2] instead
> of $(patsubst) to extract crate names for rust procmacro targets.

The implementation uses `$(basename)`, not `$(suffix)`. Please update
the commit message accordingly. Link [1] can remain, since it
documents both functions.

Otherwise this looks good to me.

> As
> there is only one user of the procmacro-extension variable, do the crate
> name extraction in-place and remove procmacro-extension.
>
> The procmacro-extension variable is used to record the binary file
> suffix of dynamically loadable rust libraries -- which is 'so' on Linux
> and others and 'dylib' in MacOS -- to remove that very suffix from a
> target file name for reconstructing the corresponding crate name in
> cmd_rustc_procmacro.  Extracting the crate name from the target name
> in-place is shorter and reduces complexity.
>
> Link: https://www.gnu.org/software/make/manual/html_node/File-Name-Functions.html # [1]
> Link: https://www.gnu.org/software/make/manual/html_node/Substitution-Refs.html # [2]
> Signed-off-by: Nicolas Schier <n.schier@xxxxxxxxx>
> ---
> Link: https://lore.kernel.org/linux-kbuild/CANiq72nmPPF=6AUp5mcDJVni80ORQr0AQ-4uCZaE+CzB5kV=eg@xxxxxxxxxxxxxx/
> ---
>  rust/Makefile | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/rust/Makefile b/rust/Makefile
> index 63b1e355321d..30f882ba7620 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -50,7 +50,6 @@ endif
>  ifdef CONFIG_RUST
>
>  procmacro-name = $(shell MAKEFLAGS= $(RUSTC) --print file-names --crate-name $(1) --crate-type proc-macro - </dev/null)
> -procmacro-extension := $(patsubst libname.%,%,$(call procmacro-name,name))
>
>  libzerocopy_derive_name := $(call procmacro-name,zerocopy_derive)
>  libmacros_name := $(call procmacro-name,macros)
> @@ -598,7 +597,7 @@ quiet_cmd_rustc_procmacro = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET))
>                 -Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \
>                 --emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
>                 --crate-type proc-macro -L$(objtree)/$(obj) \
> -               --crate-name $(patsubst lib%.$(procmacro-extension),%,$(notdir $@)) \
> +               --crate-name $(basename $(@F:lib%=%)) \
>                 @$(objtree)/include/generated/rustc_cfg $<
>
>  # Procedural macros can only be used with the `rustc` that compiled it.
>
> ---
> base-commit: b3f94b2b3f3e51ab880a51fc6510e1dafba654ed
> change-id: 20260611-rust-kbuild-replace-procmacro-extension-22c459a24382
>
> Best regards,
> --
> Nicolas Schier
>

Reviewed-by: Tamir Duberstein <tamird@xxxxxxxxxx>
Tested-by: Tamir Duberstein <tamird@xxxxxxxxxx>