linux-kernel - [PATCH v3] rust: remove spurious compiler

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Message-Id: <20250720-rust-remove-compiler-builtins-deps-v3-1-0df3a493973f@gmail.com>
Date: Sun, 20 Jul 2025 13:20:40 -0400
From: Tamir Duberstein <tamird@...il.com>
To: Miguel Ojeda <ojeda@...nel.org>, Alex Gaynor <alex.gaynor@...il.com>, 
 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>
Cc: rust-for-linux@...r.kernel.org, linux-kernel@...r.kernel.org, 
 Tamir Duberstein <tamird@...il.com>
Subject: [PATCH v3] rust: remove spurious compiler_builtins dependents

The dependency on `compiler_builtins.o` was first added in commit
2f7ab1267dc9 ("Kbuild: add Rust support") to `alloc` which matches the
standard library[0] but was copied to other targets in:
- commit ecaa6ddff2fd ("rust: add `build_error` crate")
- commit d072acda4862 ("rust: use custom FFI integer types")
- commit 4e1746656839 ("rust: uapi: Add UAPI crate")
- commit d7659acca7a3 ("rust: add pin-init crate build infrastructure")

The alloc crate was removed in commit 392e34b6bc22 ("kbuild: rust:
remove the `alloc` crate and `GlobalAlloc`"). As far as I can tell none
of the other dependencies are required; it is only required that
compiler_builtins be linked into the rust-enabled kernel. In the
standard library, compiler_builtins is a dependency of std[1].

Remove these dependency edges. Add a dependency edge from
`compiler_builtins` to `core` to `scripts/generate_rust_analyzer.py` to
match `rust/Makefile`. This has been incorrect since commit 8c4555ccc55c
("scripts: add `generate_rust_analyzer.py`")

Link: https://github.com/rust-lang/rust/blob/f820b75feef00654924c9351a2faca8d34818339/library/alloc/Cargo.toml#L19 [0]
Link: https://github.com/rust-lang/rust/blob/f820b75feef00654924c9351a2faca8d34818339/library/std/Cargo.toml#L21 [1]
Link: https://rust-for-linux.zulipchat.com/#narrow/channel/288089-General/topic/rust-analyzer.20improvements/near/510200959
Signed-off-by: Tamir Duberstein <tamird@...il.com>
---
Changes in v3:
- Fix typo in commit message (fas -> far).
- Link to v2: https://lore.kernel.org/r/20250524-rust-remove-compiler-builtins-deps-v2-1-4fc2ff489391@gmail.com

Changes in v2:
- Rebase on rust-fixes to include "scripts: generate_rust_analyzer: Add
  ffi crate".
- Link to v1: https://lore.kernel.org/r/20250408-rust-remove-compiler-builtins-deps-v1-1-4fda4f187190@gmail.com
---
 rust/Makefile                     | 6 +++---
 scripts/generate_rust_analyzer.py | 6 +++---
 2 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/rust/Makefile b/rust/Makefile
index 27dec7904c3a..5a6a381bc23d 100644
--- a/rust/Makefile
+++ b/rust/Makefile
@@ -505,16 +505,16 @@ $(obj)/compiler_builtins.o: $(src)/compiler_builtins.rs $(obj)/core.o FORCE
 $(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)/pin_init.o: $(src)/pin-init/src/lib.rs \
     $(obj)/$(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 $(obj)/compiler_builtins.o FORCE
+$(obj)/build_error.o: $(src)/build_error.rs FORCE
 	+$(call if_changed_rule,rustc_library)
 
 $(obj)/ffi.o: private skip_gendwarfksyms = 1
-$(obj)/ffi.o: $(src)/ffi.rs $(obj)/compiler_builtins.o FORCE
+$(obj)/ffi.o: $(src)/ffi.rs FORCE
 	+$(call if_changed_rule,rustc_library)
 
 $(obj)/bindings.o: private rustc_target_flags = --extern ffi
diff --git a/scripts/generate_rust_analyzer.py b/scripts/generate_rust_analyzer.py
index 7c3ea2b55041..cab9a80bed49 100755
--- a/scripts/generate_rust_analyzer.py
+++ b/scripts/generate_rust_analyzer.py
@@ -83,7 +83,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs, core_edit
     append_crate(
         "compiler_builtins",
         srctree / "rust" / "compiler_builtins.rs",
-        [],
+        ["core"],
     )
 
     append_crate(
@@ -96,7 +96,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs, core_edit
     append_crate(
         "build_error",
         srctree / "rust" / "build_error.rs",
-        ["core", "compiler_builtins"],
+        ["core"],
     )
 
     append_crate(
@@ -117,7 +117,7 @@ def generate_crates(srctree, objtree, sysroot_src, external_src, cfgs, core_edit
     append_crate(
         "ffi",
         srctree / "rust" / "ffi.rs",
-        ["core", "compiler_builtins"],
+        ["core"],
     )
 
     def append_crate_with_generated(

---
base-commit: cc84ef3b88f407e8bd5a5f7b6906d1e69851c856
change-id: 20250408-rust-remove-compiler-builtins-deps-1f061024dfce

Best regards,
--  
Tamir Duberstein <tamird@...il.com>