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, 298 insertions, 0 deletions

diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
new file mode 100644
index 000000000..895397831
--- /dev/null
+++ b/block/blk-mq-sysfs.c
@@ -0,0 +1,298 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/backing-dev.h>
+#include <linux/bio.h>
+#include <linux/blkdev.h>
+#include <linux/mm.h>
+#include <linux/init.h>
+#include <linux/slab.h>
+#include <linux/workqueue.h>
+#include <linux/smp.h>
+
+#include "blk.h"
+#include "blk-mq.h"
+
+static void blk_mq_sysfs_release(struct kobject *kobj)
+{
+	struct blk_mq_ctxs *ctxs = container_of(kobj, struct blk_mq_ctxs, kobj);
+
+	free_percpu(ctxs->queue_ctx);
+	kfree(ctxs);
+}
+
+static void blk_mq_ctx_sysfs_release(struct kobject *kobj)
+{
+	struct blk_mq_ctx *ctx = container_of(kobj, struct blk_mq_ctx, kobj);
+
+	/* ctx->ctxs won't be released until all ctx are freed */
+	kobject_put(&ctx->ctxs->kobj);
+}
+
+static void blk_mq_hw_sysfs_release(struct kobject *kobj)
+{
+	struct blk_mq_hw_ctx *hctx = container_of(kobj, struct blk_mq_hw_ctx,
+						  kobj);
+
+	sbitmap_free(&hctx->ctx_map);
+	free_cpumask_var(hctx->cpumask);
+	kfree(hctx->ctxs);
+	kfree(hctx);
+}
+
+struct blk_mq_hw_ctx_sysfs_entry {
+	struct attribute attr;
+	ssize_t (*show)(struct blk_mq_hw_ctx *, char *);
+};
+
+static ssize_t blk_mq_hw_sysfs_show(struct kobject *kobj,
+				    struct attribute *attr, char *page)
+{
+	struct blk_mq_hw_ctx_sysfs_entry *entry;
+	struct blk_mq_hw_ctx *hctx;
+	struct request_queue *q;
+	ssize_t res;
+
+	entry = container_of_const(attr, struct blk_mq_hw_ctx_sysfs_entry, attr);
+	hctx = container_of(kobj, struct blk_mq_hw_ctx, kobj);
+	q = hctx->queue;
+
+	if (!entry->show)
+		return -EIO;
+
+	mutex_lock(&q->elevator_lock);
+	res = entry->show(hctx, page);
+	mutex_unlock(&q->elevator_lock);
+	return res;
+}
+
+static ssize_t blk_mq_hw_sysfs_nr_tags_show(struct blk_mq_hw_ctx *hctx,
+					    char *page)
+{
+	return sprintf(page, "%u\n", hctx->tags->nr_tags);
+}
+
+static ssize_t blk_mq_hw_sysfs_nr_reserved_tags_show(struct blk_mq_hw_ctx *hctx,
+						     char *page)
+{
+	return sprintf(page, "%u\n", hctx->tags->nr_reserved_tags);
+}
+
+static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
+{
+	const size_t size = PAGE_SIZE - 1;
+	unsigned int i, first = 1;
+	int ret = 0, pos = 0;
+
+	for_each_cpu(i, hctx->cpumask) {
+		if (first)
+			ret = snprintf(pos + page, size - pos, "%u", i);
+		else
+			ret = snprintf(pos + page, size - pos, ", %u", i);
+
+		if (ret >= size - pos)
+			break;
+
+		first = 0;
+		pos += ret;
+	}
+
+	ret = snprintf(pos + page, size + 1 - pos, "\n");
+	return pos + ret;
+}
+
+static const struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_nr_tags = {
+	.attr = {.name = "nr_tags", .mode = 0444 },
+	.show = blk_mq_hw_sysfs_nr_tags_show,
+};
+static const struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_nr_reserved_tags = {
+	.attr = {.name = "nr_reserved_tags", .mode = 0444 },
+	.show = blk_mq_hw_sysfs_nr_reserved_tags_show,
+};
+static const struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_cpus = {
+	.attr = {.name = "cpu_list", .mode = 0444 },
+	.show = blk_mq_hw_sysfs_cpus_show,
+};
+
+static const struct attribute *const default_hw_ctx_attrs[] = {
+	&blk_mq_hw_sysfs_nr_tags.attr,
+	&blk_mq_hw_sysfs_nr_reserved_tags.attr,
+	&blk_mq_hw_sysfs_cpus.attr,
+	NULL,
+};
+ATTRIBUTE_GROUPS(default_hw_ctx);
+
+static const struct sysfs_ops blk_mq_hw_sysfs_ops = {
+	.show	= blk_mq_hw_sysfs_show,
+};
+
+static const struct kobj_type blk_mq_ktype = {
+	.release	= blk_mq_sysfs_release,
+};
+
+static const struct kobj_type blk_mq_ctx_ktype = {
+	.release	= blk_mq_ctx_sysfs_release,
+};
+
+static const struct kobj_type blk_mq_hw_ktype = {
+	.sysfs_ops	= &blk_mq_hw_sysfs_ops,
+	.default_groups = default_hw_ctx_groups,
+	.release	= blk_mq_hw_sysfs_release,
+};
+
+static void blk_mq_unregister_hctx(struct blk_mq_hw_ctx *hctx)
+{
+	struct blk_mq_ctx *ctx;
+	int i;
+
+	if (!hctx->nr_ctx)
+		return;
+
+	hctx_for_each_ctx(hctx, ctx, i)
+		if (ctx->kobj.state_in_sysfs)
+			kobject_del(&ctx->kobj);
+
+	if (hctx->kobj.state_in_sysfs)
+		kobject_del(&hctx->kobj);
+}
+
+static int blk_mq_register_hctx(struct blk_mq_hw_ctx *hctx)
+{
+	struct request_queue *q = hctx->queue;
+	struct blk_mq_ctx *ctx;
+	int i, j, ret;
+
+	if (!hctx->nr_ctx)
+		return 0;
+
+	ret = kobject_add(&hctx->kobj, q->mq_kobj, "%u", hctx->queue_num);
+	if (ret)
+		return ret;
+
+	hctx_for_each_ctx(hctx, ctx, i) {
+		ret = kobject_add(&ctx->kobj, &hctx->kobj, "cpu%u", ctx->cpu);
+		if (ret)
+			goto out;
+	}
+
+	return 0;
+out:
+	hctx_for_each_ctx(hctx, ctx, j) {
+		if (j < i)
+			kobject_del(&ctx->kobj);
+	}
+	kobject_del(&hctx->kobj);
+	return ret;
+}
+
+void blk_mq_hctx_kobj_init(struct blk_mq_hw_ctx *hctx)
+{
+	kobject_init(&hctx->kobj, &blk_mq_hw_ktype);
+}
+
+void blk_mq_sysfs_deinit(struct request_queue *q)
+{
+	struct blk_mq_ctx *ctx;
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		ctx = per_cpu_ptr(q->queue_ctx, cpu);
+		kobject_put(&ctx->kobj);
+	}
+	kobject_put(q->mq_kobj);
+}
+
+void blk_mq_sysfs_init(struct request_queue *q)
+{
+	struct blk_mq_ctx *ctx;
+	int cpu;
+
+	kobject_init(q->mq_kobj, &blk_mq_ktype);
+
+	for_each_possible_cpu(cpu) {
+		ctx = per_cpu_ptr(q->queue_ctx, cpu);
+
+		kobject_get(q->mq_kobj);
+		kobject_init(&ctx->kobj, &blk_mq_ctx_ktype);
+	}
+}
+
+int blk_mq_sysfs_register(struct gendisk *disk)
+{
+	struct request_queue *q = disk->queue;
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i, j;
+	int ret;
+
+	ret = kobject_add(q->mq_kobj, &disk_to_dev(disk)->kobj, "mq");
+	if (ret < 0)
+		return ret;
+
+	kobject_uevent(q->mq_kobj, KOBJ_ADD);
+
+	mutex_lock(&q->tag_set->tag_list_lock);
+	queue_for_each_hw_ctx(q, hctx, i) {
+		ret = blk_mq_register_hctx(hctx);
+		if (ret)
+			goto out_unreg;
+	}
+	mutex_unlock(&q->tag_set->tag_list_lock);
+	return 0;
+
+out_unreg:
+	queue_for_each_hw_ctx(q, hctx, j) {
+		if (j < i)
+			blk_mq_unregister_hctx(hctx);
+	}
+	mutex_unlock(&q->tag_set->tag_list_lock);
+
+	kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
+	kobject_del(q->mq_kobj);
+	return ret;
+}
+
+void blk_mq_sysfs_unregister(struct gendisk *disk)
+{
+	struct request_queue *q = disk->queue;
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+
+	mutex_lock(&q->tag_set->tag_list_lock);
+	queue_for_each_hw_ctx(q, hctx, i)
+		blk_mq_unregister_hctx(hctx);
+	mutex_unlock(&q->tag_set->tag_list_lock);
+
+	kobject_uevent(q->mq_kobj, KOBJ_REMOVE);
+	kobject_del(q->mq_kobj);
+}
+
+void blk_mq_sysfs_unregister_hctxs(struct request_queue *q)
+{
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+
+	if (!blk_queue_registered(q))
+		return;
+
+	queue_for_each_hw_ctx(q, hctx, i)
+		blk_mq_unregister_hctx(hctx);
+}
+
+int blk_mq_sysfs_register_hctxs(struct request_queue *q)
+{
+	struct blk_mq_hw_ctx *hctx;
+	unsigned long i;
+	int ret = 0;
+
+	if (!blk_queue_registered(q))
+		goto out;
+
+	queue_for_each_hw_ctx(q, hctx, i) {
+		ret = blk_mq_register_hctx(hctx);
+		if (ret)
+			break;
+	}
+
+out:
+	return ret;
+}