[PATCH v2 10/20] rust: proc-macro2: enable support in kbuild

Miguel Ojeda
2025-11-24T15:19:42Z

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.

In addition, skip formatting for this vendored crate and take the chance
to add a comment mentioning this.

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]
Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
---
Makefile | 5 +++++
rust/Makefile | 32 +++++++++++++++++++++++++++++--
scripts/generate_rust_analyzer.py | 7 +++++++
3 files changed, 42 insertions(+), 2 deletions(-)

diff --git a/Makefile b/Makefile
index d14824792227..589bcfe3bf75 100644
--- a/Makefile
+++ b/Makefile
@@ -1826,10 +1826,15 @@ rusttest: prepare
$(Q)$(MAKE) $(build)=rust $@

# Formatting targets
+#
+# Generated files as well as vendored crates are skipped.
PHONY += rustfmt rustfmtcheck

rustfmt:
$(Q)find $(srctree) $(RCS_FIND_IGNORE) \
+ \( \
+ -path $(srctree)/rust/proc-macro2 \
+ \) -prune -o \
-type f -a -name '*.rs' -a ! -name '*generated*' -print \
| xargs $(RUSTFMT) $(rustfmt_flags)

diff --git a/rust/Makefile b/rust/Makefile
index 0288ca8d270c..7dd1261ad98f 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)
@@ -125,10 +138,15 @@ 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
@@ -185,6 +203,10 @@ 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
@@ -431,6 +453,11 @@ quiet_cmd_rustc_procmacrolibrary = $(RUSTC_OR_CLIPPY_QUIET) PL $@
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_procmacrolibrary)
+
quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
cmd_rustc_procmacro = \
$(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
@@ -442,7 +469,7 @@ 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
@@ -465,6 +492,7 @@ 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",
--
2.52.0