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, 308 insertions, 0 deletions

diff --git a/block/bsg.c b/block/bsg.c
new file mode 100644
index 000000000..82aaf3cee
--- /dev/null
+++ b/block/bsg.c
@@ -0,0 +1,308 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * bsg.c - block layer implementation of the sg v4 interface
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/file.h>
+#include <linux/blkdev.h>
+#include <linux/cdev.h>
+#include <linux/jiffies.h>
+#include <linux/percpu.h>
+#include <linux/idr.h>
+#include <linux/bsg.h>
+#include <linux/slab.h>
+#include <linux/io_uring/cmd.h>
+
+#include <scsi/scsi.h>
+#include <scsi/scsi_ioctl.h>
+#include <scsi/sg.h>
+
+#define BSG_DESCRIPTION	"Block layer SCSI generic (bsg) driver"
+#define BSG_VERSION	"0.4"
+
+struct bsg_device {
+	struct request_queue *queue;
+	struct device device;
+	struct cdev cdev;
+	int max_queue;
+	unsigned int timeout;
+	unsigned int reserved_size;
+	bsg_sg_io_fn *sg_io_fn;
+	bsg_uring_cmd_fn *uring_cmd_fn;
+};
+
+static inline struct bsg_device *to_bsg_device(struct inode *inode)
+{
+	return container_of(inode->i_cdev, struct bsg_device, cdev);
+}
+
+#define BSG_DEFAULT_CMDS	64
+#define BSG_MAX_DEVS		(1 << MINORBITS)
+
+static DEFINE_IDA(bsg_minor_ida);
+static const struct class bsg_class;
+static int bsg_major;
+
+static unsigned int bsg_timeout(struct bsg_device *bd, struct sg_io_v4 *hdr)
+{
+	unsigned int timeout = BLK_DEFAULT_SG_TIMEOUT;
+
+	if (hdr->timeout)
+		timeout = msecs_to_jiffies(hdr->timeout);
+	else if (bd->timeout)
+		timeout = bd->timeout;
+
+	return max_t(unsigned int, timeout, BLK_MIN_SG_TIMEOUT);
+}
+
+static int bsg_sg_io(struct bsg_device *bd, bool open_for_write,
+		     void __user *uarg)
+{
+	struct sg_io_v4 hdr;
+	int ret;
+
+	if (copy_from_user(&hdr, uarg, sizeof(hdr)))
+		return -EFAULT;
+	if (hdr.guard != 'Q')
+		return -EINVAL;
+	ret = bd->sg_io_fn(bd->queue, &hdr, open_for_write,
+			   bsg_timeout(bd, &hdr));
+	if (!ret && copy_to_user(uarg, &hdr, sizeof(hdr)))
+		return -EFAULT;
+	return ret;
+}
+
+static int bsg_open(struct inode *inode, struct file *file)
+{
+	if (!blk_get_queue(to_bsg_device(inode)->queue))
+		return -ENXIO;
+	return 0;
+}
+
+static int bsg_release(struct inode *inode, struct file *file)
+{
+	blk_put_queue(to_bsg_device(inode)->queue);
+	return 0;
+}
+
+static int bsg_get_command_q(struct bsg_device *bd, int __user *uarg)
+{
+	return put_user(READ_ONCE(bd->max_queue), uarg);
+}
+
+static int bsg_set_command_q(struct bsg_device *bd, int __user *uarg)
+{
+	int max_queue;
+
+	if (get_user(max_queue, uarg))
+		return -EFAULT;
+	if (max_queue < 1)
+		return -EINVAL;
+	WRITE_ONCE(bd->max_queue, max_queue);
+	return 0;
+}
+
+static long bsg_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
+{
+	struct bsg_device *bd = to_bsg_device(file_inode(file));
+	struct request_queue *q = bd->queue;
+	void __user *uarg = (void __user *) arg;
+	int __user *intp = uarg;
+	int val;
+
+	switch (cmd) {
+	/*
+	 * Our own ioctls
+	 */
+	case SG_GET_COMMAND_Q:
+		return bsg_get_command_q(bd, uarg);
+	case SG_SET_COMMAND_Q:
+		return bsg_set_command_q(bd, uarg);
+
+	/*
+	 * SCSI/sg ioctls
+	 */
+	case SG_GET_VERSION_NUM:
+		return put_user(30527, intp);
+	case SCSI_IOCTL_GET_IDLUN:
+		return put_user(0, intp);
+	case SCSI_IOCTL_GET_BUS_NUMBER:
+		return put_user(0, intp);
+	case SG_SET_TIMEOUT:
+		if (get_user(val, intp))
+			return -EFAULT;
+		bd->timeout = clock_t_to_jiffies(val);
+		return 0;
+	case SG_GET_TIMEOUT:
+		return jiffies_to_clock_t(bd->timeout);
+	case SG_GET_RESERVED_SIZE:
+		return put_user(min(bd->reserved_size, queue_max_bytes(q)),
+				intp);
+	case SG_SET_RESERVED_SIZE:
+		if (get_user(val, intp))
+			return -EFAULT;
+		if (val < 0)
+			return -EINVAL;
+		bd->reserved_size =
+			min_t(unsigned int, val, queue_max_bytes(q));
+		return 0;
+	case SG_EMULATED_HOST:
+		return put_user(1, intp);
+	case SG_IO:
+		return bsg_sg_io(bd, file->f_mode & FMODE_WRITE, uarg);
+	case SCSI_IOCTL_SEND_COMMAND:
+		pr_warn_ratelimited("%s: calling unsupported SCSI_IOCTL_SEND_COMMAND\n",
+				current->comm);
+		return -EINVAL;
+	default:
+		return -ENOTTY;
+	}
+}
+
+static int bsg_check_uring_features(unsigned int issue_flags)
+{
+	/* BSG passthrough requires big SQE/CQE support */
+	if ((issue_flags & (IO_URING_F_SQE128|IO_URING_F_CQE32)) !=
+	    (IO_URING_F_SQE128|IO_URING_F_CQE32))
+		return -EOPNOTSUPP;
+	return 0;
+}
+
+static int bsg_uring_cmd(struct io_uring_cmd *ioucmd, unsigned int issue_flags)
+{
+	struct bsg_device *bd = to_bsg_device(file_inode(ioucmd->file));
+	bool open_for_write = ioucmd->file->f_mode & FMODE_WRITE;
+	struct request_queue *q = bd->queue;
+	int ret;
+
+	ret = bsg_check_uring_features(issue_flags);
+	if (ret)
+		return ret;
+
+	if (!bd->uring_cmd_fn)
+		return -EOPNOTSUPP;
+
+	return bd->uring_cmd_fn(q, ioucmd, issue_flags, open_for_write);
+}
+
+static const struct file_operations bsg_fops = {
+	.open		=	bsg_open,
+	.release	=	bsg_release,
+	.unlocked_ioctl	=	bsg_ioctl,
+	.compat_ioctl	=	compat_ptr_ioctl,
+	.uring_cmd	=	bsg_uring_cmd,
+	.owner		=	THIS_MODULE,
+	.llseek		=	default_llseek,
+};
+
+static void bsg_device_release(struct device *dev)
+{
+	struct bsg_device *bd = container_of(dev, struct bsg_device, device);
+
+	ida_free(&bsg_minor_ida, MINOR(bd->device.devt));
+	kfree(bd);
+}
+
+void bsg_unregister_queue(struct bsg_device *bd)
+{
+	struct gendisk *disk = bd->queue->disk;
+
+	if (disk && disk->queue_kobj.sd)
+		sysfs_remove_link(&disk->queue_kobj, "bsg");
+	cdev_device_del(&bd->cdev, &bd->device);
+	put_device(&bd->device);
+}
+EXPORT_SYMBOL_GPL(bsg_unregister_queue);
+
+struct bsg_device *bsg_register_queue(struct request_queue *q,
+		struct device *parent, const char *name, bsg_sg_io_fn *sg_io_fn,
+		bsg_uring_cmd_fn *uring_cmd_fn)
+{
+	struct bsg_device *bd;
+	int ret;
+
+	bd = kzalloc_obj(*bd);
+	if (!bd)
+		return ERR_PTR(-ENOMEM);
+	bd->max_queue = BSG_DEFAULT_CMDS;
+	bd->reserved_size = INT_MAX;
+	bd->queue = q;
+	bd->sg_io_fn = sg_io_fn;
+	bd->uring_cmd_fn = uring_cmd_fn;
+
+	ret = ida_alloc_max(&bsg_minor_ida, BSG_MAX_DEVS - 1, GFP_KERNEL);
+	if (ret < 0) {
+		if (ret == -ENOSPC)
+			dev_err(parent, "bsg: too many bsg devices\n");
+		kfree(bd);
+		return ERR_PTR(ret);
+	}
+	bd->device.devt = MKDEV(bsg_major, ret);
+	bd->device.class = &bsg_class;
+	bd->device.parent = parent;
+	bd->device.release = bsg_device_release;
+	dev_set_name(&bd->device, "%s", name);
+	device_initialize(&bd->device);
+
+	cdev_init(&bd->cdev, &bsg_fops);
+	bd->cdev.owner = THIS_MODULE;
+	ret = cdev_device_add(&bd->cdev, &bd->device);
+	if (ret)
+		goto out_put_device;
+
+	if (q->disk && q->disk->queue_kobj.sd) {
+		ret = sysfs_create_link(&q->disk->queue_kobj, &bd->device.kobj,
+					"bsg");
+		if (ret)
+			goto out_device_del;
+	}
+
+	return bd;
+
+out_device_del:
+	cdev_device_del(&bd->cdev, &bd->device);
+out_put_device:
+	put_device(&bd->device);
+	return ERR_PTR(ret);
+}
+EXPORT_SYMBOL_GPL(bsg_register_queue);
+
+static char *bsg_devnode(const struct device *dev, umode_t *mode)
+{
+	return kasprintf(GFP_KERNEL, "bsg/%s", dev_name(dev));
+}
+
+static const struct class bsg_class = {
+	.name		= "bsg",
+	.devnode	= bsg_devnode,
+};
+
+static int __init bsg_init(void)
+{
+	dev_t devid;
+	int ret;
+
+	ret = class_register(&bsg_class);
+	if (ret)
+		return ret;
+
+	ret = alloc_chrdev_region(&devid, 0, BSG_MAX_DEVS, "bsg");
+	if (ret)
+		goto destroy_bsg_class;
+	bsg_major = MAJOR(devid);
+
+	printk(KERN_INFO BSG_DESCRIPTION " version " BSG_VERSION
+	       " loaded (major %d)\n", bsg_major);
+	return 0;
+
+destroy_bsg_class:
+	class_unregister(&bsg_class);
+	return ret;
+}
+
+MODULE_AUTHOR("Jens Axboe");
+MODULE_DESCRIPTION(BSG_DESCRIPTION);
+MODULE_LICENSE("GPL");
+
+device_initcall(bsg_init);