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, 151 insertions, 0 deletions

diff --git a/drivers/md/raid5-log.h b/drivers/md/raid5-log.h
new file mode 100644
index 000000000..c83325026
--- /dev/null
+++ b/drivers/md/raid5-log.h
@@ -0,0 +1,151 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _RAID5_LOG_H
+#define _RAID5_LOG_H
+
+int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev);
+void r5l_exit_log(struct r5conf *conf);
+int r5l_write_stripe(struct r5l_log *log, struct stripe_head *head_sh);
+void r5l_write_stripe_run(struct r5l_log *log);
+void r5l_flush_stripe_to_raid(struct r5l_log *log);
+void r5l_stripe_write_finished(struct stripe_head *sh);
+int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio);
+void r5l_quiesce(struct r5l_log *log, int quiesce);
+bool r5l_log_disk_error(struct r5conf *conf);
+bool r5c_is_writeback(struct r5l_log *log);
+int r5c_try_caching_write(struct r5conf *conf, struct stripe_head *sh,
+			  struct stripe_head_state *s, int disks);
+void r5c_finish_stripe_write_out(struct r5conf *conf, struct stripe_head *sh,
+				 struct stripe_head_state *s);
+void r5c_release_extra_page(struct stripe_head *sh);
+void r5c_use_extra_page(struct stripe_head *sh);
+void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
+void r5c_handle_cached_data_endio(struct r5conf *conf,
+				  struct stripe_head *sh, int disks);
+int r5c_cache_data(struct r5l_log *log, struct stripe_head *sh);
+void r5c_make_stripe_write_out(struct stripe_head *sh);
+void r5c_flush_cache(struct r5conf *conf, int num);
+void r5c_check_stripe_cache_usage(struct r5conf *conf);
+void r5c_check_cached_full_stripe(struct r5conf *conf);
+extern struct md_sysfs_entry r5c_journal_mode;
+void r5c_update_on_rdev_error(struct mddev *mddev, struct md_rdev *rdev);
+bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect);
+int r5l_start(struct r5l_log *log);
+
+struct dma_async_tx_descriptor *
+ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
+		       struct dma_async_tx_descriptor *tx);
+int ppl_init_log(struct r5conf *conf);
+void ppl_exit_log(struct r5conf *conf);
+int ppl_write_stripe(struct r5conf *conf, struct stripe_head *sh);
+void ppl_write_stripe_run(struct r5conf *conf);
+void ppl_stripe_write_finished(struct stripe_head *sh);
+int ppl_modify_log(struct r5conf *conf, struct md_rdev *rdev, bool add);
+void ppl_quiesce(struct r5conf *conf, int quiesce);
+int ppl_handle_flush_request(struct bio *bio);
+extern struct md_sysfs_entry ppl_write_hint;
+
+static inline bool raid5_has_log(struct r5conf *conf)
+{
+	return test_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
+}
+
+static inline bool raid5_has_ppl(struct r5conf *conf)
+{
+	return test_bit(MD_HAS_PPL, &conf->mddev->flags);
+}
+
+static inline int log_stripe(struct stripe_head *sh, struct stripe_head_state *s)
+{
+	struct r5conf *conf = sh->raid_conf;
+
+	if (conf->log) {
+		if (!test_bit(STRIPE_R5C_CACHING, &sh->state)) {
+			/* writing out phase */
+			if (s->waiting_extra_page)
+				return 0;
+			return r5l_write_stripe(conf->log, sh);
+		} else if (test_bit(STRIPE_LOG_TRAPPED, &sh->state)) {
+			/* caching phase */
+			return r5c_cache_data(conf->log, sh);
+		}
+	} else if (raid5_has_ppl(conf)) {
+		return ppl_write_stripe(conf, sh);
+	}
+
+	return -EAGAIN;
+}
+
+static inline void log_stripe_write_finished(struct stripe_head *sh)
+{
+	struct r5conf *conf = sh->raid_conf;
+
+	if (conf->log)
+		r5l_stripe_write_finished(sh);
+	else if (raid5_has_ppl(conf))
+		ppl_stripe_write_finished(sh);
+}
+
+static inline void log_write_stripe_run(struct r5conf *conf)
+{
+	if (conf->log)
+		r5l_write_stripe_run(conf->log);
+	else if (raid5_has_ppl(conf))
+		ppl_write_stripe_run(conf);
+}
+
+static inline void log_flush_stripe_to_raid(struct r5conf *conf)
+{
+	if (conf->log)
+		r5l_flush_stripe_to_raid(conf->log);
+	else if (raid5_has_ppl(conf))
+		ppl_write_stripe_run(conf);
+}
+
+static inline int log_handle_flush_request(struct r5conf *conf, struct bio *bio)
+{
+	int ret = -ENODEV;
+
+	if (conf->log)
+		ret = r5l_handle_flush_request(conf->log, bio);
+	else if (raid5_has_ppl(conf))
+		ret = ppl_handle_flush_request(bio);
+
+	return ret;
+}
+
+static inline void log_quiesce(struct r5conf *conf, int quiesce)
+{
+	if (conf->log)
+		r5l_quiesce(conf->log, quiesce);
+	else if (raid5_has_ppl(conf))
+		ppl_quiesce(conf, quiesce);
+}
+
+static inline void log_exit(struct r5conf *conf)
+{
+	if (conf->log)
+		r5l_exit_log(conf);
+	else if (raid5_has_ppl(conf))
+		ppl_exit_log(conf);
+}
+
+static inline int log_init(struct r5conf *conf, struct md_rdev *journal_dev,
+			   bool ppl)
+{
+	if (journal_dev)
+		return r5l_init_log(conf, journal_dev);
+	else if (ppl)
+		return ppl_init_log(conf);
+
+	return 0;
+}
+
+static inline int log_modify(struct r5conf *conf, struct md_rdev *rdev, bool add)
+{
+	if (raid5_has_ppl(conf))
+		return ppl_modify_log(conf, rdev, add);
+
+	return 0;
+}
+
+#endif