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, 262 insertions, 0 deletions

diff --git a/drivers/md/bcache/debug.c b/drivers/md/bcache/debug.c
new file mode 100644
index 000000000..2691a5da3
--- /dev/null
+++ b/drivers/md/bcache/debug.c
@@ -0,0 +1,262 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Assorted bcache debug code
+ *
+ * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright 2012 Google, Inc.
+ */
+
+#include "bcache.h"
+#include "btree.h"
+#include "debug.h"
+#include "extents.h"
+
+#include <linux/console.h>
+#include <linux/debugfs.h>
+#include <linux/module.h>
+#include <linux/random.h>
+#include <linux/seq_file.h>
+
+struct dentry *bcache_debug;
+
+#ifdef CONFIG_BCACHE_DEBUG
+
+#define for_each_written_bset(b, start, i)				\
+	for (i = (start);						\
+	     (void *) i < (void *) (start) + (KEY_SIZE(&b->key) << 9) &&\
+	     i->seq == (start)->seq;					\
+	     i = (void *) i + set_blocks(i, block_bytes(b->c->cache)) *	\
+		 block_bytes(b->c->cache))
+
+void bch_btree_verify(struct btree *b)
+{
+	struct btree *v = b->c->verify_data;
+	struct bset *ondisk, *sorted, *inmemory;
+	struct bio *bio;
+
+	if (!b->c->verify || !b->c->verify_ondisk)
+		return;
+
+	down(&b->io_mutex);
+	mutex_lock(&b->c->verify_lock);
+
+	ondisk = b->c->verify_ondisk;
+	sorted = b->c->verify_data->keys.set->data;
+	inmemory = b->keys.set->data;
+
+	bkey_copy(&v->key, &b->key);
+	v->written = 0;
+	v->level = b->level;
+	v->keys.ops = b->keys.ops;
+
+	bio = bch_bbio_alloc(b->c);
+	bio_set_dev(bio, b->c->cache->bdev);
+	bio->bi_iter.bi_sector	= PTR_OFFSET(&b->key, 0);
+	bio->bi_iter.bi_size	= KEY_SIZE(&v->key) << 9;
+	bio->bi_opf		= REQ_OP_READ | REQ_META;
+	bch_bio_map(bio, sorted);
+
+	submit_bio_wait(bio);
+	bch_bbio_free(bio, b->c);
+
+	memcpy(ondisk, sorted, KEY_SIZE(&v->key) << 9);
+
+	bch_btree_node_read_done(v);
+	sorted = v->keys.set->data;
+
+	if (inmemory->keys != sorted->keys ||
+	    memcmp(inmemory->start,
+		   sorted->start,
+		   (void *) bset_bkey_last(inmemory) -
+		   (void *) inmemory->start)) {
+		struct bset *i;
+		unsigned int j;
+
+		console_lock();
+
+		pr_err("*** in memory:\n");
+		bch_dump_bset(&b->keys, inmemory, 0);
+
+		pr_err("*** read back in:\n");
+		bch_dump_bset(&v->keys, sorted, 0);
+
+		for_each_written_bset(b, ondisk, i) {
+			unsigned int block = ((void *) i - (void *) ondisk) /
+				block_bytes(b->c->cache);
+
+			pr_err("*** on disk block %u:\n", block);
+			bch_dump_bset(&b->keys, i, block);
+		}
+
+		pr_err("*** block %zu not written\n",
+		       ((void *) i - (void *) ondisk) / block_bytes(b->c->cache));
+
+		for (j = 0; j < inmemory->keys; j++)
+			if (inmemory->d[j] != sorted->d[j])
+				break;
+
+		pr_err("b->written %u\n", b->written);
+
+		console_unlock();
+		panic("verify failed at %u\n", j);
+	}
+
+	mutex_unlock(&b->c->verify_lock);
+	up(&b->io_mutex);
+}
+
+void bch_data_verify(struct cached_dev *dc, struct bio *bio)
+{
+	unsigned int nr_segs = bio_segments(bio);
+	struct bio *check;
+	struct bio_vec bv, cbv;
+	struct bvec_iter iter, citer = { 0 };
+
+	check = bio_kmalloc(nr_segs, GFP_NOIO);
+	if (!check)
+		return;
+	bio_init_inline(check, bio->bi_bdev, nr_segs, REQ_OP_READ);
+	check->bi_iter.bi_sector = bio->bi_iter.bi_sector;
+	check->bi_iter.bi_size = bio->bi_iter.bi_size;
+
+	bch_bio_map(check, NULL);
+	if (bch_bio_alloc_pages(check, GFP_NOIO))
+		goto out_put;
+
+	submit_bio_wait(check);
+
+	citer.bi_size = UINT_MAX;
+	bio_for_each_segment(bv, bio, iter) {
+		void *p1 = bvec_kmap_local(&bv);
+		void *p2;
+
+		cbv = bio_iter_iovec(check, citer);
+		p2 = bvec_kmap_local(&cbv);
+
+		cache_set_err_on(memcmp(p1, p2, bv.bv_len),
+				 dc->disk.c,
+				 "verify failed at dev %pg sector %llu",
+				 dc->bdev,
+				 (uint64_t) bio->bi_iter.bi_sector);
+
+		kunmap_local(p2);
+		kunmap_local(p1);
+		bio_advance_iter(check, &citer, bv.bv_len);
+	}
+
+	bio_free_pages(check);
+out_put:
+	bio_uninit(check);
+	kfree(check);
+}
+
+#endif
+
+#ifdef CONFIG_DEBUG_FS
+
+/* XXX: cache set refcounting */
+
+struct dump_iterator {
+	char			buf[PAGE_SIZE];
+	size_t			bytes;
+	struct cache_set	*c;
+	struct keybuf		keys;
+};
+
+static bool dump_pred(struct keybuf *buf, struct bkey *k)
+{
+	return true;
+}
+
+static ssize_t bch_dump_read(struct file *file, char __user *buf,
+			     size_t size, loff_t *ppos)
+{
+	struct dump_iterator *i = file->private_data;
+	ssize_t ret = 0;
+	char kbuf[80];
+
+	while (size) {
+		struct keybuf_key *w;
+		unsigned int bytes = min(i->bytes, size);
+
+		if (copy_to_user(buf, i->buf, bytes))
+			return -EFAULT;
+
+		ret	 += bytes;
+		buf	 += bytes;
+		size	 -= bytes;
+		i->bytes -= bytes;
+		memmove(i->buf, i->buf + bytes, i->bytes);
+
+		if (i->bytes)
+			break;
+
+		w = bch_keybuf_next_rescan(i->c, &i->keys, &MAX_KEY, dump_pred);
+		if (!w)
+			break;
+
+		bch_extent_to_text(kbuf, sizeof(kbuf), &w->key);
+		i->bytes = snprintf(i->buf, PAGE_SIZE, "%s\n", kbuf);
+		bch_keybuf_del(&i->keys, w);
+	}
+
+	return ret;
+}
+
+static int bch_dump_open(struct inode *inode, struct file *file)
+{
+	struct cache_set *c = inode->i_private;
+	struct dump_iterator *i;
+
+	i = kzalloc_obj(struct dump_iterator);
+	if (!i)
+		return -ENOMEM;
+
+	file->private_data = i;
+	i->c = c;
+	bch_keybuf_init(&i->keys);
+	i->keys.last_scanned = KEY(0, 0, 0);
+
+	return 0;
+}
+
+static int bch_dump_release(struct inode *inode, struct file *file)
+{
+	kfree(file->private_data);
+	return 0;
+}
+
+static const struct file_operations cache_set_debug_ops = {
+	.owner		= THIS_MODULE,
+	.open		= bch_dump_open,
+	.read		= bch_dump_read,
+	.release	= bch_dump_release
+};
+
+void bch_debug_init_cache_set(struct cache_set *c)
+{
+	if (!IS_ERR_OR_NULL(bcache_debug)) {
+		char name[50];
+
+		snprintf(name, 50, "bcache-%pU", c->set_uuid);
+		c->debug = debugfs_create_file(name, 0400, bcache_debug, c,
+					       &cache_set_debug_ops);
+	}
+}
+
+#endif
+
+void bch_debug_exit(void)
+{
+	debugfs_remove_recursive(bcache_debug);
+}
+
+void __init bch_debug_init(void)
+{
+	/*
+	 * it is unnecessary to check return value of
+	 * debugfs_create_file(), we should not care
+	 * about this.
+	 */
+	bcache_debug = debugfs_create_dir("bcache", NULL);
+}