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, 542 insertions, 0 deletions

diff --git a/drivers/mtd/mtd_blkdevs.c b/drivers/mtd/mtd_blkdevs.c
new file mode 100644
index 000000000..4d2e7b777
--- /dev/null
+++ b/drivers/mtd/mtd_blkdevs.c
@@ -0,0 +1,542 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Interface to Linux block layer for MTD 'translation layers'.
+ *
+ * Copyright © 2003-2010 David Woodhouse <dwmw2@infradead.org>
+ */
+
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/list.h>
+#include <linux/fs.h>
+#include <linux/mtd/blktrans.h>
+#include <linux/mtd/mtd.h>
+#include <linux/blkdev.h>
+#include <linux/blk-mq.h>
+#include <linux/blkpg.h>
+#include <linux/spinlock.h>
+#include <linux/hdreg.h>
+#include <linux/mutex.h>
+#include <linux/uaccess.h>
+
+#include "mtdcore.h"
+
+static LIST_HEAD(blktrans_majors);
+
+static void blktrans_dev_release(struct kref *kref)
+{
+	struct mtd_blktrans_dev *dev =
+		container_of(kref, struct mtd_blktrans_dev, ref);
+
+	put_disk(dev->disk);
+	blk_mq_free_tag_set(dev->tag_set);
+	kfree(dev->tag_set);
+	list_del(&dev->list);
+	kfree(dev);
+}
+
+static void blktrans_dev_put(struct mtd_blktrans_dev *dev)
+{
+	kref_put(&dev->ref, blktrans_dev_release);
+}
+
+
+static blk_status_t do_blktrans_request(struct mtd_blktrans_ops *tr,
+			       struct mtd_blktrans_dev *dev,
+			       struct request *req)
+{
+	struct req_iterator iter;
+	struct bio_vec bvec;
+	unsigned long block, nsect;
+	char *buf;
+
+	block = blk_rq_pos(req) << 9 >> tr->blkshift;
+	nsect = blk_rq_cur_bytes(req) >> tr->blkshift;
+
+	switch (req_op(req)) {
+	case REQ_OP_FLUSH:
+		if (tr->flush(dev))
+			return BLK_STS_IOERR;
+		return BLK_STS_OK;
+	case REQ_OP_DISCARD:
+		if (tr->discard(dev, block, nsect))
+			return BLK_STS_IOERR;
+		return BLK_STS_OK;
+	case REQ_OP_READ:
+		buf = kmap(bio_page(req->bio)) + bio_offset(req->bio);
+		for (; nsect > 0; nsect--, block++, buf += tr->blksize) {
+			if (tr->readsect(dev, block, buf)) {
+				kunmap(bio_page(req->bio));
+				return BLK_STS_IOERR;
+			}
+		}
+		kunmap(bio_page(req->bio));
+
+		rq_for_each_segment(bvec, req, iter)
+			flush_dcache_page(bvec.bv_page);
+		return BLK_STS_OK;
+	case REQ_OP_WRITE:
+		if (!tr->writesect)
+			return BLK_STS_IOERR;
+
+		rq_for_each_segment(bvec, req, iter)
+			flush_dcache_page(bvec.bv_page);
+
+		buf = kmap(bio_page(req->bio)) + bio_offset(req->bio);
+		for (; nsect > 0; nsect--, block++, buf += tr->blksize) {
+			if (tr->writesect(dev, block, buf)) {
+				kunmap(bio_page(req->bio));
+				return BLK_STS_IOERR;
+			}
+		}
+		kunmap(bio_page(req->bio));
+		return BLK_STS_OK;
+	default:
+		return BLK_STS_IOERR;
+	}
+}
+
+int mtd_blktrans_cease_background(struct mtd_blktrans_dev *dev)
+{
+	return dev->bg_stop;
+}
+EXPORT_SYMBOL_GPL(mtd_blktrans_cease_background);
+
+static struct request *mtd_next_request(struct mtd_blktrans_dev *dev)
+{
+	struct request *rq;
+
+	rq = list_first_entry_or_null(&dev->rq_list, struct request, queuelist);
+	if (rq) {
+		list_del_init(&rq->queuelist);
+		blk_mq_start_request(rq);
+		return rq;
+	}
+
+	return NULL;
+}
+
+static void mtd_blktrans_work(struct mtd_blktrans_dev *dev)
+	__releases(&dev->queue_lock)
+	__acquires(&dev->queue_lock)
+{
+	struct mtd_blktrans_ops *tr = dev->tr;
+	struct request *req = NULL;
+	int background_done = 0;
+
+	while (1) {
+		blk_status_t res;
+
+		dev->bg_stop = false;
+		if (!req && !(req = mtd_next_request(dev))) {
+			if (tr->background && !background_done) {
+				spin_unlock_irq(&dev->queue_lock);
+				mutex_lock(&dev->lock);
+				tr->background(dev);
+				mutex_unlock(&dev->lock);
+				spin_lock_irq(&dev->queue_lock);
+				/*
+				 * Do background processing just once per idle
+				 * period.
+				 */
+				background_done = !dev->bg_stop;
+				continue;
+			}
+			break;
+		}
+
+		spin_unlock_irq(&dev->queue_lock);
+
+		mutex_lock(&dev->lock);
+		res = do_blktrans_request(dev->tr, dev, req);
+		mutex_unlock(&dev->lock);
+
+		if (!blk_update_request(req, res, blk_rq_cur_bytes(req))) {
+			__blk_mq_end_request(req, res);
+			req = NULL;
+		}
+
+		background_done = 0;
+		cond_resched();
+		spin_lock_irq(&dev->queue_lock);
+	}
+}
+
+static blk_status_t mtd_queue_rq(struct blk_mq_hw_ctx *hctx,
+				 const struct blk_mq_queue_data *bd)
+{
+	struct mtd_blktrans_dev *dev;
+
+	dev = hctx->queue->queuedata;
+	if (!dev) {
+		blk_mq_start_request(bd->rq);
+		return BLK_STS_IOERR;
+	}
+
+	spin_lock_irq(&dev->queue_lock);
+	list_add_tail(&bd->rq->queuelist, &dev->rq_list);
+	mtd_blktrans_work(dev);
+	spin_unlock_irq(&dev->queue_lock);
+
+	return BLK_STS_OK;
+}
+
+static int blktrans_open(struct gendisk *disk, blk_mode_t mode)
+{
+	struct mtd_blktrans_dev *dev = disk->private_data;
+	int ret = 0;
+
+	kref_get(&dev->ref);
+
+	mutex_lock(&dev->lock);
+
+	if (dev->open)
+		goto unlock;
+
+	__module_get(dev->tr->owner);
+
+	if (!dev->mtd)
+		goto unlock;
+
+	if (dev->tr->open) {
+		ret = dev->tr->open(dev);
+		if (ret)
+			goto error_put;
+	}
+
+	ret = __get_mtd_device(dev->mtd);
+	if (ret)
+		goto error_release;
+	dev->writable = mode & BLK_OPEN_WRITE;
+
+unlock:
+	dev->open++;
+	mutex_unlock(&dev->lock);
+	return ret;
+
+error_release:
+	if (dev->tr->release)
+		dev->tr->release(dev);
+error_put:
+	module_put(dev->tr->owner);
+	mutex_unlock(&dev->lock);
+	blktrans_dev_put(dev);
+	return ret;
+}
+
+static void blktrans_release(struct gendisk *disk)
+{
+	struct mtd_blktrans_dev *dev = disk->private_data;
+
+	mutex_lock(&dev->lock);
+
+	if (--dev->open)
+		goto unlock;
+
+	module_put(dev->tr->owner);
+
+	if (dev->mtd) {
+		if (dev->tr->release)
+			dev->tr->release(dev);
+		__put_mtd_device(dev->mtd);
+	}
+unlock:
+	mutex_unlock(&dev->lock);
+	blktrans_dev_put(dev);
+}
+
+static int blktrans_getgeo(struct gendisk *disk, struct hd_geometry *geo)
+{
+	struct mtd_blktrans_dev *dev = disk->private_data;
+	int ret = -ENXIO;
+
+	mutex_lock(&dev->lock);
+
+	if (!dev->mtd)
+		goto unlock;
+
+	ret = dev->tr->getgeo ? dev->tr->getgeo(dev, geo) : -ENOTTY;
+unlock:
+	mutex_unlock(&dev->lock);
+	return ret;
+}
+
+static const struct block_device_operations mtd_block_ops = {
+	.owner		= THIS_MODULE,
+	.open		= blktrans_open,
+	.release	= blktrans_release,
+	.getgeo		= blktrans_getgeo,
+};
+
+static const struct blk_mq_ops mtd_mq_ops = {
+	.queue_rq	= mtd_queue_rq,
+};
+
+int add_mtd_blktrans_dev(struct mtd_blktrans_dev *new)
+{
+	struct mtd_blktrans_ops *tr = new->tr;
+	struct mtd_blktrans_dev *d;
+	struct queue_limits lim = { };
+	int last_devnum = -1;
+	struct gendisk *gd;
+	int ret;
+
+	lockdep_assert_held(&mtd_table_mutex);
+
+	list_for_each_entry(d, &tr->devs, list) {
+		if (new->devnum == -1) {
+			/* Use first free number */
+			if (d->devnum != last_devnum+1) {
+				/* Found a free devnum. Plug it in here */
+				new->devnum = last_devnum+1;
+				list_add_tail(&new->list, &d->list);
+				goto added;
+			}
+		} else if (d->devnum == new->devnum) {
+			/* Required number taken */
+			return -EBUSY;
+		} else if (d->devnum > new->devnum) {
+			/* Required number was free */
+			list_add_tail(&new->list, &d->list);
+			goto added;
+		}
+		last_devnum = d->devnum;
+	}
+
+	ret = -EBUSY;
+	if (new->devnum == -1)
+		new->devnum = last_devnum+1;
+
+	/* Check that the device and any partitions will get valid
+	 * minor numbers and that the disk naming code below can cope
+	 * with this number. */
+	if (new->devnum > (MINORMASK >> tr->part_bits) ||
+	    (tr->part_bits && new->devnum >= 27 * 26))
+		return ret;
+
+	list_add_tail(&new->list, &tr->devs);
+ added:
+
+	mutex_init(&new->lock);
+	kref_init(&new->ref);
+	if (!tr->writesect)
+		new->readonly = 1;
+
+	ret = -ENOMEM;
+	new->tag_set = kzalloc_obj(*new->tag_set);
+	if (!new->tag_set)
+		goto out_list_del;
+
+	ret = blk_mq_alloc_sq_tag_set(new->tag_set, &mtd_mq_ops, 2,
+			BLK_MQ_F_BLOCKING);
+	if (ret)
+		goto out_kfree_tag_set;
+	
+	lim.logical_block_size = tr->blksize;
+	if (tr->discard)
+		lim.max_hw_discard_sectors = UINT_MAX;
+	if (tr->flush)
+		lim.features |= BLK_FEAT_WRITE_CACHE;
+
+	/* Create gendisk */
+	gd = blk_mq_alloc_disk(new->tag_set, &lim, new);
+	if (IS_ERR(gd)) {
+		ret = PTR_ERR(gd);
+		goto out_free_tag_set;
+	}
+
+	new->disk = gd;
+	new->rq = new->disk->queue;
+	gd->private_data = new;
+	gd->major = tr->major;
+	gd->first_minor = (new->devnum) << tr->part_bits;
+	gd->minors = 1 << tr->part_bits;
+	gd->fops = &mtd_block_ops;
+
+	if (tr->part_bits) {
+		if (new->devnum < 26)
+			snprintf(gd->disk_name, sizeof(gd->disk_name),
+				 "%s%c", tr->name, 'a' + new->devnum);
+		else
+			snprintf(gd->disk_name, sizeof(gd->disk_name),
+				 "%s%c%c", tr->name,
+				 'a' - 1 + new->devnum / 26,
+				 'a' + new->devnum % 26);
+	} else {
+		snprintf(gd->disk_name, sizeof(gd->disk_name),
+			 "%s%d", tr->name, new->devnum);
+		gd->flags |= GENHD_FL_NO_PART;
+	}
+
+	set_capacity(gd, ((u64)new->size * tr->blksize) >> 9);
+
+	/* Create the request queue */
+	spin_lock_init(&new->queue_lock);
+	INIT_LIST_HEAD(&new->rq_list);
+	gd->queue = new->rq;
+
+	if (new->readonly)
+		set_disk_ro(gd, 1);
+
+	ret = device_add_disk(&new->mtd->dev, gd, NULL);
+	if (ret)
+		goto out_cleanup_disk;
+
+	if (new->disk_attributes) {
+		ret = sysfs_create_group(&disk_to_dev(gd)->kobj,
+					new->disk_attributes);
+		WARN_ON(ret);
+	}
+	return 0;
+
+out_cleanup_disk:
+	put_disk(new->disk);
+out_free_tag_set:
+	blk_mq_free_tag_set(new->tag_set);
+out_kfree_tag_set:
+	kfree(new->tag_set);
+out_list_del:
+	list_del(&new->list);
+	return ret;
+}
+
+int del_mtd_blktrans_dev(struct mtd_blktrans_dev *old)
+{
+	unsigned long flags;
+	unsigned int memflags;
+
+	lockdep_assert_held(&mtd_table_mutex);
+
+	if (old->disk_attributes)
+		sysfs_remove_group(&disk_to_dev(old->disk)->kobj,
+						old->disk_attributes);
+
+	/* Stop new requests to arrive */
+	del_gendisk(old->disk);
+
+	/* Kill current requests */
+	spin_lock_irqsave(&old->queue_lock, flags);
+	old->rq->queuedata = NULL;
+	spin_unlock_irqrestore(&old->queue_lock, flags);
+
+	/* freeze+quiesce queue to ensure all requests are flushed */
+	memflags = blk_mq_freeze_queue(old->rq);
+	blk_mq_quiesce_queue(old->rq);
+	blk_mq_unquiesce_queue(old->rq);
+	blk_mq_unfreeze_queue(old->rq, memflags);
+
+	/* If the device is currently open, tell trans driver to close it,
+		then put mtd device, and don't touch it again */
+	mutex_lock(&old->lock);
+	if (old->open) {
+		if (old->tr->release)
+			old->tr->release(old);
+		__put_mtd_device(old->mtd);
+	}
+
+	old->mtd = NULL;
+
+	mutex_unlock(&old->lock);
+	blktrans_dev_put(old);
+	return 0;
+}
+
+static void blktrans_notify_remove(struct mtd_info *mtd)
+{
+	struct mtd_blktrans_ops *tr;
+	struct mtd_blktrans_dev *dev, *next;
+
+	list_for_each_entry(tr, &blktrans_majors, list)
+		list_for_each_entry_safe(dev, next, &tr->devs, list)
+			if (dev->mtd == mtd)
+				tr->remove_dev(dev);
+}
+
+static void blktrans_notify_add(struct mtd_info *mtd)
+{
+	struct mtd_blktrans_ops *tr;
+
+	if (mtd->type == MTD_ABSENT || mtd->type == MTD_UBIVOLUME)
+		return;
+
+	list_for_each_entry(tr, &blktrans_majors, list)
+		tr->add_mtd(tr, mtd);
+}
+
+static struct mtd_notifier blktrans_notifier = {
+	.add = blktrans_notify_add,
+	.remove = blktrans_notify_remove,
+};
+
+int register_mtd_blktrans(struct mtd_blktrans_ops *tr)
+{
+	struct mtd_info *mtd;
+	int ret;
+
+	/* Register the notifier if/when the first device type is
+	   registered, to prevent the link/init ordering from fucking
+	   us over. */
+	if (!blktrans_notifier.list.next)
+		register_mtd_user(&blktrans_notifier);
+
+	ret = register_blkdev(tr->major, tr->name);
+	if (ret < 0) {
+		printk(KERN_WARNING "Unable to register %s block device on major %d: %d\n",
+		       tr->name, tr->major, ret);
+		return ret;
+	}
+
+	if (ret)
+		tr->major = ret;
+
+	tr->blkshift = ffs(tr->blksize) - 1;
+
+	INIT_LIST_HEAD(&tr->devs);
+
+	mutex_lock(&mtd_table_mutex);
+	list_add(&tr->list, &blktrans_majors);
+	mtd_for_each_device(mtd)
+		if (mtd->type != MTD_ABSENT && mtd->type != MTD_UBIVOLUME)
+			tr->add_mtd(tr, mtd);
+	mutex_unlock(&mtd_table_mutex);
+	return 0;
+}
+
+int deregister_mtd_blktrans(struct mtd_blktrans_ops *tr)
+{
+	struct mtd_blktrans_dev *dev, *next;
+
+	mutex_lock(&mtd_table_mutex);
+
+	/* Remove it from the list of active majors */
+	list_del(&tr->list);
+
+	list_for_each_entry_safe(dev, next, &tr->devs, list)
+		tr->remove_dev(dev);
+
+	mutex_unlock(&mtd_table_mutex);
+	unregister_blkdev(tr->major, tr->name);
+
+	BUG_ON(!list_empty(&tr->devs));
+	return 0;
+}
+
+static void __exit mtd_blktrans_exit(void)
+{
+	/* No race here -- if someone's currently in register_mtd_blktrans
+	   we're screwed anyway. */
+	if (blktrans_notifier.list.next)
+		unregister_mtd_user(&blktrans_notifier);
+}
+
+module_exit(mtd_blktrans_exit);
+
+EXPORT_SYMBOL_GPL(register_mtd_blktrans);
+EXPORT_SYMBOL_GPL(deregister_mtd_blktrans);
+EXPORT_SYMBOL_GPL(add_mtd_blktrans_dev);
+EXPORT_SYMBOL_GPL(del_mtd_blktrans_dev);
+
+MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Common interface to block layer for MTD 'translation layers'");