Split bindings crate out of the main kernel crate

The generated bindings are mostly static when working on new rust
abstractions. By splitting them off the main kernel crate, recompilation
of the main kernel crate takes ~2s rather than ~12s. While this loses
some optimizations without LTO, the fast majority of the binding
functions are already marked as `#[inline]`. Pretty much only
`Default` impls aren't marked as such. The cost of not inlining those
`Default` impls is likely neglectable.

Signed-off-by: Björn Roy Baron <[email protected]>

Author: bjorn3

rust/Makefile

@@ -15,7 +15,7 @@ always-$(CONFIG_RUST) += libmacros.so
 no-clean-files += libmacros.so
 
 always-$(CONFIG_RUST) += bindings_generated.rs bindings_helpers_generated.rs
-obj-$(CONFIG_RUST) += alloc.o kernel.o
+obj-$(CONFIG_RUST) += alloc.o bindings.o kernel.o
 always-$(CONFIG_RUST) += exports_alloc_generated.h exports_kernel_generated.h
 
 ifdef CONFIG_RUST_BUILD_ASSERT_DENY
@@ -110,10 +110,11 @@ rustdoc-alloc: $(src)/alloc/lib.rs rustdoc-core rustdoc-compiler_builtins FORCE
 	$(call if_changed,rustdoc)
 
 rustdoc-kernel: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so
+    --extern build_error --extern macros=$(objtree)/$(obj)/libmacros.so \
+	--extern bindings
 rustdoc-kernel: $(src)/kernel/lib.rs rustdoc-core rustdoc-macros \
     rustdoc-compiler_builtins rustdoc-alloc $(obj)/libmacros.so \
-    $(obj)/bindings_generated.rs $(obj)/bindings_helpers_generated.rs FORCE
+    $(obj)/bindings.o FORCE
 	$(call if_changed,rustdoc)
 
 quiet_cmd_rustc_test_library = RUSTC TL $<
@@ -154,6 +155,7 @@ quiet_cmd_rustdoc_test_kernel = RUSTDOC TK $<
 		@$(objtree)/include/generated/rustc_cfg \
 		-L$(objtree)/$(obj) --extern alloc --extern kernel \
 		--extern build_error --extern macros \
+		--extern bindings \
 		--no-run --crate-name kernel -Zunstable-options \
 		--test-builder $(srctree)/scripts/rustdoc_test_builder.py \
 		$< $(rustdoc_test_kernel_quiet); \
@@ -234,8 +236,7 @@ rusttest-macros: $(src)/macros/lib.rs rusttest-prepare FORCE
 	$(call if_changed,rustdoc_test)
 
 rusttest-kernel: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros
-rusttest-kernel: private rustc_test_run_flags = --skip bindgen_test_layout_
+    --extern build_error --extern macros --extern bindings
 rusttest-kernel: $(src)/kernel/lib.rs rusttest-prepare \
     rusttestlib-build_error rusttestlib-macros FORCE
 	$(call if_changed,rustc_test)
@@ -388,11 +389,16 @@ $(obj)/alloc.o: $(src)/alloc/lib.rs $(obj)/compiler_builtins.o FORCE
 $(obj)/build_error.o: $(src)/build_error.rs $(obj)/compiler_builtins.o FORCE
 	$(call if_changed_dep,rustc_library)
 
+$(obj)/bindings.o: $(src)/kernel/bindings.rs \
+	$(obj)/compiler_builtins.o \
+    $(obj)/bindings_generated.rs \
+    $(obj)/bindings_helpers_generated.rs FORCE
+	$(call if_changed_dep,rustc_library)
+
 $(obj)/kernel.o: private rustc_target_flags = --extern alloc \
-    --extern build_error --extern macros
+    --extern build_error --extern macros --extern bindings
 $(obj)/kernel.o: $(src)/kernel/lib.rs $(obj)/alloc.o $(obj)/build_error.o \
-    $(obj)/libmacros.so $(obj)/bindings_generated.rs \
-    $(obj)/bindings_helpers_generated.rs FORCE
+    $(obj)/libmacros.so $(obj)/bindings.o FORCE
 	$(call if_changed_dep,rustc_library)
 
 endif # CONFIG_RUST

rust/kernel/bindings.rs

@@ -3,13 +3,20 @@
 //! Bindings.
 //!
 //! Imports the generated bindings by `bindgen`.
+//!
+//! This crate may not be directly used. If you need a kernel C API that is
+//! not ported or wrapped in the kernel crate, then do so first instead of
+//! using this crate.
 
+#![no_std]
+#![feature(core_ffi_c)]
 // See https://github.com/rust-lang/rust-bindgen/issues/1651.
 #![cfg_attr(test, allow(deref_nullptr))]
 #![cfg_attr(test, allow(unaligned_references))]
 #![cfg_attr(test, allow(unsafe_op_in_unsafe_fn))]
 #![allow(
     clippy::all,
+    missing_docs,
     non_camel_case_types,
     non_upper_case_globals,
     non_snake_case,

rust/kernel/lib.rs

@@ -39,7 +39,7 @@ compile_error!("Missing kernel configuration for conditional compilation");
 mod allocator;
 
 #[doc(hidden)]
-pub mod bindings;
+pub use bindings;
 
 #[cfg(CONFIG_ARM_AMBA)]
 pub mod amba;

scripts/generate_rust_analyzer.py

@@ -73,13 +73,20 @@ def append_crate(display_name, root_module, deps, cfg=[], is_workspace_member=Tr
         ["core", "compiler_builtins"],
     )
 
+    append_crate(
+        "bindings",
+        srctree / "rust"/ "kernel" / "bindings.rs",
+        ["core"],
+        cfg=cfg,
+    )
+    crates[-1]["env"]["OBJTREE"] = str(objtree.resolve(True))
+
     append_crate(
         "kernel",
         srctree / "rust" / "kernel" / "lib.rs",
-        ["core", "alloc", "macros", "build_error"],
+        ["core", "alloc", "macros", "build_error", "bindings"],
         cfg=cfg,
     )
-    crates[-1]["env"]["OBJTREE"] = str(objtree.resolve(True))
     crates[-1]["source"] = {
         "include_dirs": [
             str(srctree / "rust" / "kernel"),