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, 91 insertions, 0 deletions

diff --git a/block/blk-mq-debugfs.h b/block/blk-mq-debugfs.h
new file mode 100644
index 000000000..49bb1aaa8
--- /dev/null
+++ b/block/blk-mq-debugfs.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef INT_BLK_MQ_DEBUGFS_H
+#define INT_BLK_MQ_DEBUGFS_H
+
+#ifdef CONFIG_BLK_DEBUG_FS
+
+#include <linux/seq_file.h>
+
+struct blk_mq_hw_ctx;
+
+struct blk_mq_debugfs_attr {
+	const char *name;
+	umode_t mode;
+	int (*show)(void *, struct seq_file *);
+	ssize_t (*write)(void *, const char __user *, size_t, loff_t *);
+	/* Set either .show or .seq_ops. */
+	const struct seq_operations *seq_ops;
+};
+
+int __blk_mq_debugfs_rq_show(struct seq_file *m, struct request *rq);
+int blk_mq_debugfs_rq_show(struct seq_file *m, void *v);
+
+void blk_mq_debugfs_register(struct request_queue *q);
+void blk_mq_debugfs_register_hctx(struct request_queue *q,
+				  struct blk_mq_hw_ctx *hctx);
+void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx);
+void blk_mq_debugfs_register_hctxs(struct request_queue *q);
+void blk_mq_debugfs_unregister_hctxs(struct request_queue *q);
+
+void blk_mq_debugfs_register_sched(struct request_queue *q);
+void blk_mq_debugfs_unregister_sched(struct request_queue *q);
+void blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
+				       struct blk_mq_hw_ctx *hctx);
+void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx);
+
+void blk_mq_debugfs_register_rq_qos(struct request_queue *q);
+#else
+static inline void blk_mq_debugfs_register(struct request_queue *q)
+{
+}
+
+static inline void blk_mq_debugfs_register_hctx(struct request_queue *q,
+						struct blk_mq_hw_ctx *hctx)
+{
+}
+
+static inline void blk_mq_debugfs_unregister_hctx(struct blk_mq_hw_ctx *hctx)
+{
+}
+
+static inline void blk_mq_debugfs_register_hctxs(struct request_queue *q)
+{
+}
+
+static inline void blk_mq_debugfs_unregister_hctxs(struct request_queue *q)
+{
+}
+
+static inline void blk_mq_debugfs_register_sched(struct request_queue *q)
+{
+}
+
+static inline void blk_mq_debugfs_unregister_sched(struct request_queue *q)
+{
+}
+
+static inline void blk_mq_debugfs_register_sched_hctx(struct request_queue *q,
+						      struct blk_mq_hw_ctx *hctx)
+{
+}
+
+static inline void blk_mq_debugfs_unregister_sched_hctx(struct blk_mq_hw_ctx *hctx)
+{
+}
+
+static inline void blk_mq_debugfs_register_rq_qos(struct request_queue *q)
+{
+}
+
+#endif
+
+#if defined(CONFIG_BLK_DEV_ZONED) && defined(CONFIG_BLK_DEBUG_FS)
+int queue_zone_wplugs_show(void *data, struct seq_file *m);
+#else
+static inline int queue_zone_wplugs_show(void *data, struct seq_file *m)
+{
+	return 0;
+}
+#endif
+
+#endif