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, 85 insertions, 0 deletions

diff --git a/block/bio-integrity-fs.c b/block/bio-integrity-fs.c
new file mode 100644
index 000000000..9c5fe5fa8
--- /dev/null
+++ b/block/bio-integrity-fs.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2025 Christoph Hellwig.
+ */
+#include <linux/blk-integrity.h>
+#include <linux/bio-integrity.h>
+#include "blk.h"
+
+struct fs_bio_integrity_buf {
+	struct bio_integrity_payload	bip;
+	struct bio_vec			bvec;
+};
+
+static struct kmem_cache *fs_bio_integrity_cache;
+static mempool_t fs_bio_integrity_pool;
+
+unsigned int fs_bio_integrity_alloc(struct bio *bio)
+{
+	struct fs_bio_integrity_buf *iib;
+	unsigned int action;
+
+	action = bio_integrity_action(bio);
+	if (!action)
+		return 0;
+
+	iib = mempool_alloc(&fs_bio_integrity_pool, GFP_NOFS);
+	bio_integrity_init(bio, &iib->bip, &iib->bvec, 1);
+
+	bio_integrity_alloc_buf(bio, GFP_NOFS, action & BI_ACT_ZERO);
+	if (action & BI_ACT_CHECK)
+		bio_integrity_setup_default(bio);
+	return action;
+}
+
+void fs_bio_integrity_free(struct bio *bio)
+{
+	struct bio_integrity_payload *bip = bio_integrity(bio);
+
+	bio_integrity_free_buf(bip);
+	mempool_free(container_of(bip, struct fs_bio_integrity_buf, bip),
+			&fs_bio_integrity_pool);
+
+	bio->bi_integrity = NULL;
+	bio->bi_opf &= ~REQ_INTEGRITY;
+}
+
+void fs_bio_integrity_generate(struct bio *bio)
+{
+	if (fs_bio_integrity_alloc(bio))
+		bio_integrity_generate(bio);
+}
+EXPORT_SYMBOL_GPL(fs_bio_integrity_generate);
+
+int fs_bio_integrity_verify(struct bio *bio, sector_t sector, unsigned int size)
+{
+	struct blk_integrity *bi = blk_get_integrity(bio->bi_bdev->bd_disk);
+	struct bio_integrity_payload *bip = bio_integrity(bio);
+	struct bvec_iter data_iter = {
+		.bi_sector	= sector,
+		.bi_size	= size,
+	};
+
+	/*
+	 * Reinitialize bip->bip_iter.
+	 *
+	 * This is for use in the submitter after the driver is done with the
+	 * bio.  Requires the submitter to remember the sector and the size.
+	 */
+	memset(&bip->bip_iter, 0, sizeof(bip->bip_iter));
+	bip->bip_iter.bi_sector = sector;
+	bip->bip_iter.bi_size = bio_integrity_bytes(bi, size >> SECTOR_SHIFT);
+	return blk_status_to_errno(bio_integrity_verify(bio, &data_iter));
+}
+
+static int __init fs_bio_integrity_init(void)
+{
+	fs_bio_integrity_cache = kmem_cache_create("fs_bio_integrity",
+			sizeof(struct fs_bio_integrity_buf), 0,
+			SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
+	if (mempool_init_slab_pool(&fs_bio_integrity_pool, BIO_POOL_SIZE,
+			fs_bio_integrity_cache))
+		panic("fs_bio_integrity: can't create pool\n");
+	return 0;
+}
+fs_initcall(fs_bio_integrity_init);