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| author | Miguel Ojeda <ojeda@kernel.org> | 2026-08-16 15:32:32 +0200 |
|---|---|---|
| committer | Miguel Ojeda <ojeda@kernel.org> | 2026-08-23 21:27:17 +0200 |
| commit | 0bff7711c19ba05ff3b686554c5a2d503c3e9797 (patch) | |
| tree | 472c17033dcaa413fc533eea74c54dbebdcc0949 /rust | |
| parent | 29b03d1de967a177176d12811d970cac7882afcf (diff) | |
| download | linux-next-0bff7711c19ba05ff3b686554c5a2d503c3e9797.tar.gz linux-next-0bff7711c19ba05ff3b686554c5a2d503c3e9797.zip | |
kbuild: rust: preserve unreachable traps with inline helpers
When `CONFIG_RUST_INLINE_HELPERS` is enabled, it is possible to hit
`objtool` warnings like:
vmlinux.o: warning: objtool: _R..._4cmdq12CommandToGsp4init()
falls through to next function _R..._4core5array4iter8IntoIterRShKj3_EEEBa_()
`rustc` normally emits traps for unreachable paths. However, under
`CONFIG_RUST_INLINE_HELPERS=y`, `rustc` emits LLVM bitcode and Clang
performs final code generation after the helper bitcode is linked,
but Clang does not trap unreachable IR by default.
In turn, this means `objtool` follows compiler-generated impossible Rust
`enum` paths through alignment padding into the next function, resulting
in fallthrough warnings.
Thus pass the LLVM `trap-unreachable` option to the final Clang invocation
and suppress traps immediately after `noreturn` calls, which `objtool`
already recognizes as dead ends. The combination of both flags makes it
match `rustc`'s behavior.
Rust 1.85.0 (the minimum supported one) supports LLVM >= 18, and both
flags are available in LLVM 18.
Assisted-by: LLM
Cc: Gary Guo <gary@garyguo.net>
Cc: Boqun Feng <boqun@kernel.org>
Cc: Alice Ryhl <aliceryhl@google.com>
Cc: Matthew Maurer <mmaurer@google.com>
Cc: Josh Poimboeuf <jpoimboe@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: stable@vger.kernel.org
Fixes: 3a2486cc1da5 ("kbuild: rust: provide an option to inline C helpers into Rust")
Acked-by: Gary Guo <gary@garyguo.net>
Link: https://patch.msgid.link/20260816133233.197500-1-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>
Diffstat (limited to 'rust')
| -rw-r--r-- | rust/Makefile | 3 |
1 files changed, 2 insertions, 1 deletions
diff --git a/rust/Makefile b/rust/Makefile index fbe0accc51a3..f871d94f6af2 100644 --- a/rust/Makefile +++ b/rust/Makefile @@ -644,7 +644,8 @@ quiet_cmd_rustc_library = $(if $(skip_clippy),RUSTC,$(RUSTC_OR_CLIPPY_QUIET)) L -Zunstable-options \ $(if $(link_helper),;$(LLVM_LINK) --internalize --suppress-warnings $(patsubst %.o,%.bc,$@) \ $(obj)/helpers/helpers$(if $(part-of-module),_module).bc -o $(patsubst %.o,%.m.bc,$@); \ - $(CC) $(CLANG_FLAGS) $(KBUILD_CFLAGS) -Wno-override-module -c $(patsubst %.o,%.m.bc,$@) -o $@ \ + $(CC) $(CLANG_FLAGS) $(KBUILD_CFLAGS) \ + $(CC_FLAGS_RUST_INLINE_HELPERS) -Wno-override-module -c $(patsubst %.o,%.m.bc,$@) -o $@ \ $(cmd_ld_single)) \ $(if $(rustc_objcopy),;$(OBJCOPY) $(rustc_objcopy) $@) \ $(cmd_objtool) |