Message-ID: <98e549da-b7d5-45bc-8a9c-d05eb06a75e6@nvidia.com>
Date: Mon, 10 Nov 2025 11:34:18 -0800
From: John Hubbard <jhubbard@...dia.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>,
 Nathan Chancellor <nathan@...nel.org>, Nicolas Schier <nicolas@...sle.eu>
Cc: Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
 Björn Roy Baron <bjorn3_gh@...tonmail.com>,
 Benno Lossin <lossin@...nel.org>, Andreas Hindborg <a.hindborg@...nel.org>,
 Alice Ryhl <aliceryhl@...gle.com>, Trevor Gross <tmgross@...ch.edu>,
 Danilo Krummrich <dakr@...nel.org>, rust-for-linux@...r.kernel.org,
 linux-kbuild@...r.kernel.org, linux-kernel@...r.kernel.org,
 patches@...ts.linux.dev
Subject: Re: [PATCH 09/18] rust: proc-macro2: enable support in kbuild

On 11/10/25 1:50 AM, Miguel Ojeda wrote:
> With all the new files in place and ready from the new crate, enable
> the support for it in the build system.
> 
> `proc_macro_byte_character` and `proc_macro_c_str_literals` were
> stabilized in Rust 1.79.0 [1] and were implemented earlier than our
> minimum Rust version (1.78) [2][3]. Thus just enable them instead of using
> the `cfg` that `proc-macro2` uses to emulate them in older compilers.
> 
> Link: https://github.com/rust-lang/rust/pull/123431 [1]
> Link: https://github.com/rust-lang/rust/pull/112711 [2]
> Link: https://github.com/rust-lang/rust/pull/119651 [3]
> Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
> ---
>  Makefile                          |  3 +++
>  rust/Makefile                     | 32 +++++++++++++++++++++++++++++--
>  scripts/generate_rust_analyzer.py |  7 +++++++
>  3 files changed, 40 insertions(+), 2 deletions(-)
> 
> diff --git a/Makefile b/Makefile
> index fb4389aa5d5f..6ff887523eee 100644
> --- a/Makefile
> +++ b/Makefile
> @@ -1830,6 +1830,9 @@ PHONY += rustfmt rustfmtcheck
>  
>  rustfmt:
>  	$(Q)find $(srctree) $(RCS_FIND_IGNORE) \
> +		\( \
> +			-path $(srctree)/rust/proc-macro2 \
> +		\) -prune -o \

Looks good. But for future code and commit log readers, should
we leave a small comment, to explain that this was vendored in,
and therefore excluded from "make rustfmt"?

An alternative approach might be to create a "vendored" subdir,
to make it clear which parts of the Rust for Linux code are
special in that way.

thanks,
-- 
John Hubbard

>  		-type f -a -name '*.rs' -a ! -name '*generated*' -print \
>  		| xargs $(RUSTFMT) $(rustfmt_flags)
>  
> diff --git a/rust/Makefile b/rust/Makefile
> index 9eea6563ef35..a614a23023cb 100644
> --- a/rust/Makefile
> +++ b/rust/Makefile
> @@ -27,6 +27,8 @@ endif
>  
>  obj-$(CONFIG_RUST) += exports.o
>  
> +always-$(CONFIG_RUST) += libproc_macro2.rlib
> +
>  always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated.rs
>  always-$(CONFIG_RUST_KERNEL_DOCTESTS) += doctests_kernel_generated_kunit.c
>  
> @@ -76,6 +78,17 @@ core-flags := \
>      --edition=$(core-edition) \
>      $(call cfgs-to-flags,$(core-cfgs))
>  
> +proc_macro2-cfgs := \
> +    feature="proc-macro" \
> +    wrap_proc_macro \
> +    $(if $(call rustc-min-version,108800),proc_macro_span_file proc_macro_span_location)
> +
> +# Stable since Rust 1.79.0: `feature(proc_macro_byte_character,proc_macro_c_str_literals)`.
> +proc_macro2-flags := \
> +    --cap-lints=allow \
> +    -Zcrate-attr='feature(proc_macro_byte_character,proc_macro_c_str_literals)' \
> +    $(call cfgs-to-flags,$(proc_macro2-cfgs))
> +
>  # `rustdoc` did not save the target modifiers, thus workaround for
>  # the time being (https://github.com/rust-lang/rust/issues/144521).
>  rustdoc_modifiers_workaround := $(if $(call rustc-min-version,108800),-Cunsafe-allow-abi-mismatch=fixed-x18)
> @@ -128,10 +141,15 @@ rustdoc: rustdoc-core rustdoc-macros rustdoc-compiler_builtins \
>  	$(Q)for f in $(rustdoc_output)/static.files/rustdoc-*.css; do \
>  		echo ".logo-container > img { object-fit: contain; }" >> $$f; done
>  
> +rustdoc-proc_macro2: private rustdoc_host = yes
> +rustdoc-proc_macro2: private rustc_target_flags = $(proc_macro2-flags)
> +rustdoc-proc_macro2: $(src)/proc-macro2/lib.rs rustdoc-clean FORCE
> +	+$(call if_changed,rustdoc)
> +
>  rustdoc-macros: private rustdoc_host = yes
>  rustdoc-macros: private rustc_target_flags = --crate-type proc-macro \
>      --extern proc_macro
> -rustdoc-macros: $(src)/macros/lib.rs rustdoc-clean FORCE
> +rustdoc-macros: $(src)/macros/lib.rs rustdoc-clean rustdoc-proc_macro2 FORCE
>  	+$(call if_changed,rustdoc)
>  
>  # Starting with Rust 1.82.0, skipping `-Wrustdoc::unescaped_backticks` should
> @@ -194,6 +212,10 @@ rusttestlib-build_error: $(src)/build_error.rs FORCE
>  rusttestlib-ffi: $(src)/ffi.rs FORCE
>  	+$(call if_changed,rustc_test_library)
>  
> +rusttestlib-proc_macro2: private rustc_target_flags = $(proc_macro2-flags)
> +rusttestlib-proc_macro2: $(src)/proc-macro2/lib.rs FORCE
> +	+$(call if_changed,rustc_test_library)
> +
>  rusttestlib-macros: private rustc_target_flags = --extern proc_macro
>  rusttestlib-macros: private rustc_test_library_proc = yes
>  rusttestlib-macros: $(src)/macros/lib.rs FORCE
> @@ -440,6 +462,11 @@ quiet_cmd_rustc_hostlibrary = $(RUSTC_OR_CLIPPY_QUIET) H $@
>  	mv $(objtree)/$(obj)/$(patsubst lib%.rlib,%,$(notdir $@)).d $(depfile); \
>  	sed -i '/^\#/d' $(depfile)
>  
> +$(obj)/libproc_macro2.rlib: private skip_clippy = 1
> +$(obj)/libproc_macro2.rlib: private rustc_target_flags = $(proc_macro2-flags)
> +$(obj)/libproc_macro2.rlib: $(src)/proc-macro2/lib.rs FORCE
> +	+$(call if_changed_dep,rustc_hostlibrary)
> +
>  quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>        cmd_rustc_procmacro = \
>  	$(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
> @@ -451,7 +478,7 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
>  		@$(objtree)/include/generated/rustc_cfg $<
>  
>  # Procedural macros can only be used with the `rustc` that compiled it.
> -$(obj)/$(libmacros_name): $(src)/macros/lib.rs FORCE
> +$(obj)/$(libmacros_name): $(src)/macros/lib.rs $(obj)/libproc_macro2.rlib FORCE
>  	+$(call if_changed_dep,rustc_procmacro)
>  
>  $(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel
> @@ -474,6 +501,7 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L
>  rust-analyzer:
>  	$(Q)MAKEFLAGS= $(srctree)/scripts/generate_rust_analyzer.py \
>  		--cfgs='core=$(core-cfgs)' $(core-edition) \
> +		--cfgs='proc_macro2=$(proc_macro2-cfgs)' \
>  		$(realpath $(srctree)) $(realpath $(objtree)) \
>  		$(rustc_sysroot) $(RUST_LIB_SRC) $(if $(KBUILD_EXTMOD),$(srcroot)) \
>  		> rust-project.json
> diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
> index dedca470adc1..00c6b7cc94b7 100755
> --- a/scripts/generate_rust_analyzer.py
> +++ b/scripts/generate_rust_analyzer.py
> @@ -86,6 +86,13 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs, core_edit
>          [],
>      )
>  
> +    append_crate(
> +        "proc_macro2",
> +        srctree / "rust" / "proc-macro2" / "lib.rs",
> +        ["core", "alloc", "std", "proc_macro"],
> +        cfg=crates_cfgs["proc_macro2"],
> +    )
> +
>      append_crate(
>          "macros",
>          srctree / "rust" / "macros" / "lib.rs",

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