kbuild: rust: keep Rust objects out of Clang LTO with inline helpersgrafted

Under `CONFIG_LTO_CLANG` + `CONFIG_RUST_INLINE_HELPERS`, one may hit
`objtool` errors such as:

    vmlinux.o: error: objtool: _R..._3Gsp4boot+0xd6a:
    can't find jump dest instruction at .text._R..._3Gsp4boot+0x1dfd

The reason is that in such builds, the Clang invocation that compiles
the combined Rust plus helpers bitcode emits LLVM bitcode (again) --
the final code generation happens in the linker's LTO step, which the
`-mllvm` trap options passed to Clang do not reach.

This, in turn, means that unreachable traps are missing, and the
impossible paths do not merely fallthrough to the next symbol, but past
the end of their own section, since LTO builds place each function in
its own section.

Thus filter `CC_FLAGS_LTO` out of the Clang invocation, so that it always
emits machine code directly, with the traps in place.

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/20260816133233.197500-2-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

1 files changed, 47 insertions, 0 deletions

diff --git a/drivers/md/bcache/request.h b/drivers/md/bcache/request.h
new file mode 100644
index 000000000..46bbef00a
--- /dev/null
+++ b/drivers/md/bcache/request.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _BCACHE_REQUEST_H_
+#define _BCACHE_REQUEST_H_
+
+struct data_insert_op {
+	struct closure		cl;
+	struct cache_set	*c;
+	struct bio		*bio;
+	struct workqueue_struct *wq;
+
+	unsigned int		inode;
+	uint16_t		write_point;
+	uint16_t		write_prio;
+	blk_status_t		status;
+
+	union {
+		uint16_t	flags;
+
+	struct {
+		unsigned int	bypass:1;
+		unsigned int	writeback:1;
+		unsigned int	flush_journal:1;
+		unsigned int	csum:1;
+
+		unsigned int	replace:1;
+		unsigned int	replace_collision:1;
+
+		unsigned int	insert_data_done:1;
+	};
+	};
+
+	struct keylist		insert_keys;
+	BKEY_PADDED(replace_key);
+};
+
+unsigned int bch_get_congested(const struct cache_set *c);
+CLOSURE_CALLBACK(bch_data_insert);
+
+void bch_cached_dev_request_init(struct cached_dev *dc);
+void cached_dev_submit_bio(struct bio *bio);
+
+void bch_flash_dev_request_init(struct bcache_device *d);
+void flash_dev_submit_bio(struct bio *bio);
+
+extern struct kmem_cache *bch_search_cache;
+
+#endif /* _BCACHE_REQUEST_H_ */