rust: add pin-init crate build infrastructure

Add infrastructure for moving the initialization API to its own crate.
Covers all make targets such as `rust-analyzer` and `rustdoc`. The tests
of pin-init are not added to `rusttest`, as they are already tested in
the user-space repository [1].

Link: https://github.com/Rust-for-Linux/pin-init [1]
Co-developed-by: Benno Lossin <benno.lossin@proton.me>
Signed-off-by: Benno Lossin <benno.lossin@proton.me>
Tested-by: Andreas Hindborg <a.hindborg@kernel.org>
Link: https://lore.kernel.org/r/20250308110339.2997091-15-benno.lossin@proton.me
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

4 files changed, 69 insertions, 18 deletions

diff --git a/rust/Makefile b/rust/Makefile
index ea3849eb78f6..90310f0620eb 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -12,7 +12,7 @@ obj-$(CONFIG_RUST) += helpers/helpers.o
 CFLAGS_REMOVE_helpers/helpers.o = -Wmissing-prototypes -Wmissing-declarations
 
 always-$(CONFIG_RUST) += bindings/bindings_generated.rs bindings/bindings_helpers_generated.rs
-obj-$(CONFIG_RUST) += bindings.o kernel.o
+obj-$(CONFIG_RUST) += bindings.o pin_init.o kernel.o
 always-$(CONFIG_RUST) += exports_helpers_generated.h \
     exports_bindings_generated.h exports_kernel_generated.h
 
@@ -41,7 +41,10 @@ ifdef CONFIG_RUST
 libmacros_name := $(shell MAKEFLAGS= $(RUSTC) --print file-names --crate-name macros --crate-type proc-macro - </dev/null)
 libmacros_extension := $(patsubst libmacros.%,%,$(libmacros_name))
 
-always-$(CONFIG_RUST) += $(libmacros_name)
+libpin_init_internal_name := $(shell MAKEFLAGS= $(RUSTC) --print file-names --crate-name pin_init_internal --crate-type proc-macro - </dev/null)
+libpin_init_internal_extension := $(patsubst libpin_init_internal.%,%,$(libpin_init_internal_name))
+
+always-$(CONFIG_RUST) += $(libmacros_name) $(libpin_init_internal_name)
 
 # `$(rust_flags)` is passed in case the user added `--sysroot`.
 rustc_sysroot := $(shell MAKEFLAGS= $(RUSTC) $(rust_flags) --print sysroot)
@@ -80,7 +83,7 @@ quiet_cmd_rustdoc = RUSTDOC $(if $(rustdoc_host),H, ) $<
 # command-like flags to solve the issue. Meanwhile, we use the non-custom case
 # and then retouch the generated files.
 rustdoc: rustdoc-core rustdoc-macros rustdoc-compiler_builtins \
-    rustdoc-kernel
+    rustdoc-kernel rustdoc-pin_init
 	$(Q)cp $(srctree)/Documentation/images/logo.svg $(rustdoc_output)/static.files/
 	$(Q)cp $(srctree)/Documentation/images/COPYING-logo $(rustdoc_output)/static.files/
 	$(Q)find $(rustdoc_output) -name '*.html' -type f -print0 | xargs -0 sed -Ei \
@@ -110,11 +113,24 @@ rustdoc-compiler_builtins: $(src)/compiler_builtins.rs rustdoc-core FORCE
 rustdoc-ffi: $(src)/ffi.rs rustdoc-core FORCE
 	+$(call if_changed,rustdoc)
 
-rustdoc-kernel: private rustc_target_flags = --extern ffi \
+rustdoc-pin_init_internal: private rustdoc_host = yes
+rustdoc-pin_init_internal: private rustc_target_flags = --cfg kernel \
+    --extern proc_macro --crate-type proc-macro
+rustdoc-pin_init_internal: $(src)/pin-init/internal/src/_lib.rs FORCE
+	+$(call if_changed,rustdoc)
+
+rustdoc-pin_init: private rustdoc_host = yes
+rustdoc-pin_init: private rustc_target_flags = --extern pin_init_internal \
+    --extern macros --extern alloc --cfg kernel --cfg feature=\"alloc\"
+rustdoc-pin_init: $(src)/pin-init/src/_lib.rs rustdoc-pin_init_internal \
+    rustdoc-macros FORCE
+	+$(call if_changed,rustdoc)
+
+rustdoc-kernel: private rustc_target_flags = --extern ffi --extern pin_init \
     --extern build_error --extern macros \
     --extern bindings --extern uapi
 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-ffi rustdoc-macros \
-    rustdoc-compiler_builtins $(obj)/$(libmacros_name) \
+    rustdoc-pin_init rustdoc-compiler_builtins $(obj)/$(libmacros_name) \
     $(obj)/bindings.o FORCE
 	+$(call if_changed,rustdoc)
 
@@ -139,12 +155,24 @@ rusttestlib-macros: private rustc_test_library_proc = yes
 rusttestlib-macros: $(src)/macros/lib.rs FORCE
 	+$(call if_changed,rustc_test_library)
 
+rusttestlib-pin_init_internal: private rustc_target_flags = --cfg kernel \
+    --extern proc_macro
+rusttestlib-pin_init_internal: private rustc_test_library_proc = yes
+rusttestlib-pin_init_internal: $(src)/pin-init/internal/src/_lib.rs FORCE
+	+$(call if_changed,rustc_test_library)
+
+rusttestlib-pin_init: private rustc_target_flags = --extern pin_init_internal \
+    --extern macros --cfg kernel
+rusttestlib-pin_init: $(src)/pin-init/src/_lib.rs rusttestlib-macros \
+    rusttestlib-pin_init_internal $(obj)/$(libpin_init_internal_name) FORCE
+	+$(call if_changed,rustc_test_library)
+
 rusttestlib-kernel: private rustc_target_flags = --extern ffi \
-    --extern build_error --extern macros \
+    --extern build_error --extern macros --extern pin_init \
     --extern bindings --extern uapi
-rusttestlib-kernel: $(src)/kernel/lib.rs \
-    rusttestlib-bindings rusttestlib-uapi rusttestlib-build_error \
-    $(obj)/$(libmacros_name) $(obj)/bindings.o FORCE
+rusttestlib-kernel: $(src)/kernel/lib.rs rusttestlib-bindings rusttestlib-uapi \
+    rusttestlib-build_error rusttestlib-pin_init $(obj)/$(libmacros_name) \
+    $(obj)/bindings.o FORCE
 	+$(call if_changed,rustc_test_library)
 
 rusttestlib-bindings: private rustc_target_flags = --extern ffi
@@ -172,8 +200,8 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 	mkdir -p $(objtree)/$(obj)/test/doctests/kernel; \
 	OBJTREE=$(abspath $(objtree)) \
 	$(RUSTDOC) --test $(rust_flags) \
-		-L$(objtree)/$(obj) --extern ffi --extern kernel \
-		--extern build_error --extern macros \
+		-L$(objtree)/$(obj) --extern ffi --extern pin_init \
+		--extern kernel --extern build_error --extern macros \
 		--extern bindings --extern uapi \
 		--no-run --crate-name kernel -Zunstable-options \
 		--sysroot=/dev/null \
@@ -203,18 +231,18 @@ quiet_cmd_rustc_test = $(RUSTC_OR_CLIPPY_QUIET) T  $<
 rusttest: rusttest-macros rusttest-kernel
 
 rusttest-macros: private rustc_target_flags = --extern proc_macro \
-	--extern macros --extern kernel
+	--extern macros --extern kernel --extern pin_init
 rusttest-macros: private rustdoc_test_target_flags = --crate-type proc-macro
 rusttest-macros: $(src)/macros/lib.rs \
-    rusttestlib-macros rusttestlib-kernel FORCE
+    rusttestlib-macros rusttestlib-kernel rusttestlib-pin_init FORCE
 	+$(call if_changed,rustc_test)
 	+$(call if_changed,rustdoc_test)
 
-rusttest-kernel: private rustc_target_flags = --extern ffi \
+rusttest-kernel: private rustc_target_flags = --extern ffi --extern pin_init \
     --extern build_error --extern macros --extern bindings --extern uapi
 rusttest-kernel: $(src)/kernel/lib.rs rusttestlib-ffi rusttestlib-kernel \
     rusttestlib-build_error rusttestlib-macros rusttestlib-bindings \
-    rusttestlib-uapi FORCE
+    rusttestlib-uapi rusttestlib-pin_init FORCE
 	+$(call if_changed,rustc_test)
 
 ifdef CONFIG_CC_IS_CLANG
@@ -361,7 +389,7 @@ $(obj)/exports_kernel_generated.h: $(obj)/kernel.o FORCE
 
 quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
       cmd_rustc_procmacro = \
-	$(RUSTC_OR_CLIPPY) $(rust_common_flags) \
+	$(RUSTC_OR_CLIPPY) $(rust_common_flags) $(rustc_target_flags) \
 		-Clinker-flavor=gcc -Clinker=$(HOSTCC) \
 		-Clink-args='$(call escsq,$(KBUILD_PROCMACROLDFLAGS))' \
 		--emit=dep-info=$(depfile) --emit=link=$@ --extern proc_macro \
@@ -372,6 +400,10 @@ quiet_cmd_rustc_procmacro = $(RUSTC_OR_CLIPPY_QUIET) P $@
 $(obj)/$(libmacros_name): $(src)/macros/lib.rs FORCE
 	+$(call if_changed_dep,rustc_procmacro)
 
+$(obj)/$(libpin_init_internal_name): private rustc_target_flags = --cfg kernel
+$(obj)/$(libpin_init_internal_name): $(src)/pin-init/internal/src/_lib.rs FORCE
+	+$(call if_changed_dep,rustc_procmacro)
+
 quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L $@
       cmd_rustc_library = \
 	OBJTREE=$(abspath $(objtree)) \
@@ -451,6 +483,13 @@ $(obj)/compiler_builtins.o: private rustc_objcopy = -w -W '__*'
 $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
+$(obj)/pin_init.o: private skip_gendwarfksyms = 1
+$(obj)/pin_init.o: private rustc_target_flags = --extern pin_init_internal \
+    --extern macros --cfg kernel
+$(obj)/pin_init.o: $(src)/pin-init/src/_lib.rs $(obj)/compiler_builtins.o \
+    $(obj)/$(libpin_init_internal_name) $(obj)/$(libmacros_name) FORCE
+	+$(call if_changed_rule,rustc_library)
+
 $(obj)/build_error.o: private skip_gendwarfksyms = 1
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	+$(call if_changed_rule,rustc_library)
@@ -473,9 +512,9 @@ $(obj)/uapi.o: $(src)/uapi/lib.rs \
     $(obj)/uapi/uapi_generated.rs FORCE
 	+$(call if_changed_rule,rustc_library)
 
-$(obj)/kernel.o: private rustc_target_flags = --extern ffi \
+$(obj)/kernel.o: private rustc_target_flags = --extern ffi --extern pin_init \
     --extern build_error --extern macros --extern bindings --extern uapi
-$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o \
+$(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/build_error.o $(obj)/pin_init.o \
     $(obj)/$(libmacros_name) $(obj)/bindings.o $(obj)/uapi.o FORCE
 	+$(call if_changed_rule,rustc_library)
 
diff --git a/rust/pin-init/internal/src/_lib.rs b/rust/pin-init/internal/src/_lib.rs
new file mode 100644
index 000000000000..0874cf04e4cb
--- /dev/null
+++ b/rust/pin-init/internal/src/_lib.rs
@@ -0,0 +1,3 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Will be removed in a future commit, only exists to prevent compilation errors.
diff --git a/rust/pin-init/internal/src/lib.rs b/rust/pin-init/internal/src/lib.rs
index bf66cbee2531..3146da5cc47c 100644
--- a/rust/pin-init/internal/src/lib.rs
+++ b/rust/pin-init/internal/src/lib.rs
@@ -1,5 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0 OR MIT
 
+// When fixdep scans this, it will find this string `CONFIG_RUSTC_VERSION_TEXT`
+// and thus add a dependency on `include/config/RUSTC_VERSION_TEXT`, which is
+// touched by Kconfig when the version string from the compiler changes.
+
 #[allow(missing_docs)]
 #[proc_macro_attribute]
 pub fn pin_data(inner: TokenStream, item: TokenStream) -> TokenStream {
diff --git a/rust/pin-init/src/_lib.rs b/rust/pin-init/src/_lib.rs
new file mode 100644
index 000000000000..e0918fd8e9e7
--- /dev/null
+++ b/rust/pin-init/src/_lib.rs
@@ -0,0 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+//! Will be removed in a future commit, only exists to prevent compilation errors.
+
+#![no_std]