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, 156 insertions, 0 deletions

diff --git a/fs/ubifs/sysfs.c b/fs/ubifs/sysfs.c
new file mode 100644
index 000000000..dbf967dcf
--- /dev/null
+++ b/fs/ubifs/sysfs.c
@@ -0,0 +1,156 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * This file is part of UBIFS.
+ *
+ * Copyright (C) 2021 Cisco Systems
+ *
+ * Author: Stefan Schaeckeler
+ */
+
+
+#include <linux/fs.h>
+#include "ubifs.h"
+
+enum attr_id_t {
+	attr_errors_magic,
+	attr_errors_node,
+	attr_errors_crc,
+};
+
+struct ubifs_attr {
+	struct attribute attr;
+	enum attr_id_t attr_id;
+};
+
+#define UBIFS_ATTR(_name, _mode, _id)					\
+static struct ubifs_attr ubifs_attr_##_name = {				\
+	.attr = {.name = __stringify(_name), .mode = _mode },		\
+	.attr_id = attr_##_id,						\
+}
+
+#define UBIFS_ATTR_FUNC(_name, _mode) UBIFS_ATTR(_name, _mode, _name)
+
+UBIFS_ATTR_FUNC(errors_magic, 0444);
+UBIFS_ATTR_FUNC(errors_crc, 0444);
+UBIFS_ATTR_FUNC(errors_node, 0444);
+
+#define ATTR_LIST(name) (&ubifs_attr_##name.attr)
+
+static struct attribute *ubifs_attrs[] = {
+	ATTR_LIST(errors_magic),
+	ATTR_LIST(errors_node),
+	ATTR_LIST(errors_crc),
+	NULL,
+};
+ATTRIBUTE_GROUPS(ubifs);
+
+static ssize_t ubifs_attr_show(struct kobject *kobj,
+			       struct attribute *attr, char *buf)
+{
+	struct ubifs_info *sbi = container_of(kobj, struct ubifs_info,
+					      kobj);
+
+	struct ubifs_attr *a = container_of(attr, struct ubifs_attr, attr);
+
+	switch (a->attr_id) {
+	case attr_errors_magic:
+		return sysfs_emit(buf, "%u\n", sbi->stats->magic_errors);
+	case attr_errors_node:
+		return sysfs_emit(buf, "%u\n", sbi->stats->node_errors);
+	case attr_errors_crc:
+		return sysfs_emit(buf, "%u\n", sbi->stats->crc_errors);
+	}
+	return 0;
+};
+
+static void ubifs_sb_release(struct kobject *kobj)
+{
+	struct ubifs_info *c = container_of(kobj, struct ubifs_info, kobj);
+
+	complete(&c->kobj_unregister);
+}
+
+static const struct sysfs_ops ubifs_attr_ops = {
+	.show	= ubifs_attr_show,
+};
+
+static const struct kobj_type ubifs_sb_ktype = {
+	.default_groups	= ubifs_groups,
+	.sysfs_ops	= &ubifs_attr_ops,
+	.release	= ubifs_sb_release,
+};
+
+static const struct kobj_type ubifs_ktype = {
+	.sysfs_ops	= &ubifs_attr_ops,
+};
+
+static struct kset ubifs_kset = {
+	.kobj	= {.ktype = &ubifs_ktype},
+};
+
+int ubifs_sysfs_register(struct ubifs_info *c)
+{
+	int ret, n;
+	char dfs_dir_name[UBIFS_DFS_DIR_LEN];
+
+	c->stats = kzalloc_obj(struct ubifs_stats_info);
+	if (!c->stats) {
+		ret = -ENOMEM;
+		goto out_last;
+	}
+	n = snprintf(dfs_dir_name, UBIFS_DFS_DIR_LEN, UBIFS_DFS_DIR_NAME,
+		     c->vi.ubi_num, c->vi.vol_id);
+
+	if (n >= UBIFS_DFS_DIR_LEN) {
+		/* The array size is too small */
+		ret = -EINVAL;
+		goto out_free;
+	}
+
+	c->kobj.kset = &ubifs_kset;
+	init_completion(&c->kobj_unregister);
+
+	ret = kobject_init_and_add(&c->kobj, &ubifs_sb_ktype, NULL,
+				   "%s", dfs_dir_name);
+	if (ret)
+		goto out_put;
+
+	return 0;
+
+out_put:
+	kobject_put(&c->kobj);
+	wait_for_completion(&c->kobj_unregister);
+out_free:
+	kfree(c->stats);
+out_last:
+	ubifs_err(c, "cannot create sysfs entry for ubifs%d_%d, error %d\n",
+		  c->vi.ubi_num, c->vi.vol_id, ret);
+	return ret;
+}
+
+void ubifs_sysfs_unregister(struct ubifs_info *c)
+{
+	kobject_del(&c->kobj);
+	kobject_put(&c->kobj);
+	wait_for_completion(&c->kobj_unregister);
+
+	kfree(c->stats);
+}
+
+int __init ubifs_sysfs_init(void)
+{
+	int ret;
+
+	kobject_set_name(&ubifs_kset.kobj, "ubifs");
+	ubifs_kset.kobj.parent = fs_kobj;
+	ret = kset_register(&ubifs_kset);
+	if (ret)
+		kset_put(&ubifs_kset);
+
+	return ret;
+}
+
+void ubifs_sysfs_exit(void)
+{
+	kset_unregister(&ubifs_kset);
+}