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, 406 insertions, 0 deletions

diff --git a/fs/kernfs/inode.c b/fs/kernfs/inode.c
new file mode 100644
index 000000000..2cb20294a
--- /dev/null
+++ b/fs/kernfs/inode.c
@@ -0,0 +1,406 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * fs/kernfs/inode.c - kernfs inode implementation
+ *
+ * Copyright (c) 2001-3 Patrick Mochel
+ * Copyright (c) 2007 SUSE Linux Products GmbH
+ * Copyright (c) 2007, 2013 Tejun Heo <tj@kernel.org>
+ */
+
+#include <linux/pagemap.h>
+#include <linux/backing-dev.h>
+#include <linux/capability.h>
+#include <linux/errno.h>
+#include <linux/slab.h>
+#include <linux/xattr.h>
+#include <linux/security.h>
+
+#include "kernfs-internal.h"
+
+static const struct inode_operations kernfs_iops = {
+	.permission	= kernfs_iop_permission,
+	.setattr	= kernfs_iop_setattr,
+	.getattr	= kernfs_iop_getattr,
+	.listxattr	= kernfs_iop_listxattr,
+};
+
+static struct kernfs_iattrs *__kernfs_iattrs(struct kernfs_node *kn, bool alloc)
+{
+	struct kernfs_iattrs *ret __free(kfree) = NULL;
+	struct kernfs_iattrs *attr;
+
+	attr = READ_ONCE(kn->iattr);
+	if (attr || !alloc)
+		return attr;
+
+	ret = kmem_cache_zalloc(kernfs_iattrs_cache, GFP_KERNEL);
+	if (!ret)
+		return NULL;
+
+	INIT_LIST_HEAD_RCU(&ret->xattrs);
+	/* assign default attributes */
+	ret->ia_uid = GLOBAL_ROOT_UID;
+	ret->ia_gid = GLOBAL_ROOT_GID;
+
+	ktime_get_real_ts64(&ret->ia_atime);
+	ret->ia_mtime = ret->ia_atime;
+	ret->ia_ctime = ret->ia_atime;
+
+	simple_xattr_limits_init(&ret->xattr_limits);
+
+	/* If someone raced us, recognize it. */
+	if (!try_cmpxchg(&kn->iattr, &attr, ret))
+		return READ_ONCE(kn->iattr);
+
+	return no_free_ptr(ret);
+}
+
+static struct kernfs_iattrs *kernfs_iattrs(struct kernfs_node *kn)
+{
+	return __kernfs_iattrs(kn, true);
+}
+
+static struct kernfs_iattrs *kernfs_iattrs_noalloc(struct kernfs_node *kn)
+{
+	return __kernfs_iattrs(kn, false);
+}
+
+int __kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
+{
+	struct kernfs_iattrs *attrs;
+	unsigned int ia_valid = iattr->ia_valid;
+
+	attrs = kernfs_iattrs(kn);
+	if (!attrs)
+		return -ENOMEM;
+
+	if (ia_valid & ATTR_UID)
+		attrs->ia_uid = iattr->ia_uid;
+	if (ia_valid & ATTR_GID)
+		attrs->ia_gid = iattr->ia_gid;
+	if (ia_valid & ATTR_ATIME)
+		attrs->ia_atime = iattr->ia_atime;
+	if (ia_valid & ATTR_MTIME)
+		attrs->ia_mtime = iattr->ia_mtime;
+	if (ia_valid & ATTR_CTIME)
+		attrs->ia_ctime = iattr->ia_ctime;
+	if (ia_valid & ATTR_MODE)
+		kn->mode = iattr->ia_mode;
+	return 0;
+}
+
+/**
+ * kernfs_setattr - set iattr on a node
+ * @kn: target node
+ * @iattr: iattr to set
+ *
+ * Return: %0 on success, -errno on failure.
+ */
+int kernfs_setattr(struct kernfs_node *kn, const struct iattr *iattr)
+{
+	int ret;
+	struct kernfs_root *root = kernfs_root(kn);
+
+	down_write(&root->kernfs_iattr_rwsem);
+	ret = __kernfs_setattr(kn, iattr);
+	up_write(&root->kernfs_iattr_rwsem);
+	return ret;
+}
+
+int kernfs_iop_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+		       struct iattr *iattr)
+{
+	struct inode *inode = d_inode(dentry);
+	struct kernfs_node *kn = inode->i_private;
+	struct kernfs_root *root;
+	int error;
+
+	if (!kn)
+		return -EINVAL;
+
+	root = kernfs_root(kn);
+	down_write(&root->kernfs_iattr_rwsem);
+	error = setattr_prepare(&nop_mnt_idmap, dentry, iattr);
+	if (error)
+		goto out;
+
+	error = __kernfs_setattr(kn, iattr);
+	if (error)
+		goto out;
+
+	/* this ignores size changes */
+	setattr_copy(&nop_mnt_idmap, inode, iattr);
+
+out:
+	up_write(&root->kernfs_iattr_rwsem);
+	return error;
+}
+
+ssize_t kernfs_iop_listxattr(struct dentry *dentry, char *buf, size_t size)
+{
+	struct kernfs_node *kn = kernfs_dentry_node(dentry);
+	struct kernfs_iattrs *attrs;
+
+	attrs = kernfs_iattrs(kn);
+	if (!attrs)
+		return -ENOMEM;
+
+	return simple_xattr_list(d_inode(dentry), &attrs->xattrs, buf, size);
+}
+
+static inline void set_default_inode_attr(struct inode *inode, umode_t mode)
+{
+	inode->i_mode = mode;
+	simple_inode_init_ts(inode);
+}
+
+static inline void set_inode_attr(struct inode *inode,
+				  struct kernfs_iattrs *attrs)
+{
+	inode->i_uid = attrs->ia_uid;
+	inode->i_gid = attrs->ia_gid;
+	inode_set_atime_to_ts(inode, attrs->ia_atime);
+	inode_set_mtime_to_ts(inode, attrs->ia_mtime);
+	inode_set_ctime_to_ts(inode, attrs->ia_ctime);
+}
+
+static void kernfs_refresh_inode(struct kernfs_node *kn, struct inode *inode)
+{
+	struct kernfs_iattrs *attrs;
+
+	inode->i_mode = kn->mode;
+	attrs = kernfs_iattrs_noalloc(kn);
+	if (attrs)
+		/*
+		 * kernfs_node has non-default attributes get them from
+		 * persistent copy in kernfs_node.
+		 */
+		set_inode_attr(inode, attrs);
+
+	if (kernfs_type(kn) == KERNFS_DIR && !(kn->flags & KERNFS_REMOVING))
+		set_nlink(inode, kn->dir.subdirs + 2);
+}
+
+int kernfs_iop_getattr(struct mnt_idmap *idmap,
+		       const struct path *path, struct kstat *stat,
+		       u32 request_mask, unsigned int query_flags)
+{
+	struct inode *inode = d_inode(path->dentry);
+	struct kernfs_node *kn = inode->i_private;
+	struct kernfs_root *root = kernfs_root(kn);
+
+	down_read(&root->kernfs_iattr_rwsem);
+	kernfs_refresh_inode(kn, inode);
+	generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat);
+	up_read(&root->kernfs_iattr_rwsem);
+
+	return 0;
+}
+
+static void kernfs_init_inode(struct kernfs_node *kn, struct inode *inode)
+{
+	kernfs_get(kn);
+	inode->i_private = kn;
+	inode->i_mapping->a_ops = &ram_aops;
+	inode->i_op = &kernfs_iops;
+	inode->i_generation = kernfs_gen(kn);
+
+	set_default_inode_attr(inode, kn->mode);
+	kernfs_refresh_inode(kn, inode);
+
+	/* initialize inode according to type */
+	switch (kernfs_type(kn)) {
+	case KERNFS_DIR:
+		inode->i_op = &kernfs_dir_iops;
+		inode->i_fop = &kernfs_dir_fops;
+		if (kn->flags & KERNFS_EMPTY_DIR)
+			make_empty_dir_inode(inode);
+		break;
+	case KERNFS_FILE:
+		inode->i_size = kn->attr.size;
+		inode->i_fop = &kernfs_file_fops;
+		break;
+	case KERNFS_LINK:
+		inode->i_op = &kernfs_symlink_iops;
+		break;
+	default:
+		BUG();
+	}
+
+	unlock_new_inode(inode);
+}
+
+/**
+ *	kernfs_get_inode - get inode for kernfs_node
+ *	@sb: super block
+ *	@kn: kernfs_node to allocate inode for
+ *
+ *	Get inode for @kn.  If such inode doesn't exist, a new inode is
+ *	allocated and basics are initialized.  New inode is returned
+ *	locked.
+ *
+ *	Locking:
+ *	Kernel thread context (may sleep).
+ *
+ *	Return:
+ *	Pointer to allocated inode on success, %NULL on failure.
+ */
+struct inode *kernfs_get_inode(struct super_block *sb, struct kernfs_node *kn)
+{
+	struct inode *inode;
+
+	inode = iget_locked(sb, kernfs_ino(kn));
+	if (inode && (inode_state_read_once(inode) & I_NEW))
+		kernfs_init_inode(kn, inode);
+
+	return inode;
+}
+
+/*
+ * The kernfs_node serves as both an inode and a directory entry for
+ * kernfs.  To prevent the kernfs inode numbers from being freed
+ * prematurely we take a reference to kernfs_node from the kernfs inode.  A
+ * super_operations.evict_inode() implementation is needed to drop that
+ * reference upon inode destruction.
+ */
+void kernfs_evict_inode(struct inode *inode)
+{
+	struct kernfs_node *kn = inode->i_private;
+
+	truncate_inode_pages_final(&inode->i_data);
+	clear_inode(inode);
+	kernfs_put(kn);
+}
+
+int kernfs_iop_permission(struct mnt_idmap *idmap,
+			  struct inode *inode, int mask)
+{
+	struct kernfs_node *kn;
+	struct kernfs_root *root;
+	int ret;
+
+	if (mask & MAY_NOT_BLOCK)
+		return -ECHILD;
+
+	kn = inode->i_private;
+	root = kernfs_root(kn);
+
+	down_read(&root->kernfs_iattr_rwsem);
+	kernfs_refresh_inode(kn, inode);
+	ret = generic_permission(&nop_mnt_idmap, inode, mask);
+	up_read(&root->kernfs_iattr_rwsem);
+
+	return ret;
+}
+
+int kernfs_xattr_get(struct kernfs_node *kn, const char *name,
+		     void *value, size_t size)
+{
+	struct kernfs_iattrs *attrs = kernfs_iattrs_noalloc(kn);
+	struct simple_xattr_cache *cache = &kernfs_root(kn)->xa_cache;
+
+	if (!attrs)
+		return -ENODATA;
+
+	return simple_xattr_get(cache, &attrs->xattrs, name, value, size);
+}
+
+int kernfs_xattr_set(struct kernfs_node *kn, const char *name,
+		     const void *value, size_t size, int flags)
+{
+	struct simple_xattr *old_xattr;
+	struct kernfs_iattrs *attrs;
+	struct simple_xattr_cache *cache = &kernfs_root(kn)->xa_cache;
+
+	attrs = kernfs_iattrs(kn);
+	if (!attrs)
+		return -ENOMEM;
+
+	/*
+	 * Protect xattr modifications with the hashed per-node mutex.
+	 * Multiple superblocks (with different namespaces) can share the same
+	 * kernfs_node, so inode locking alone is insufficient. The hashed mutex
+	 * ensures serialization of concurrent xattr operations on the same node,
+	 * including the lazy allocation of the xattrs structure itself.
+	 */
+	CLASS(kernfs_node_lock, lock)(kn);
+
+	old_xattr = simple_xattr_set(cache, &attrs->xattrs, name, value, size, flags);
+	if (IS_ERR(old_xattr))
+		return PTR_ERR(old_xattr);
+
+	simple_xattr_free_rcu(old_xattr);
+	return 0;
+}
+
+static int kernfs_vfs_xattr_get(const struct xattr_handler *handler,
+				struct dentry *unused, struct inode *inode,
+				const char *suffix, void *value, size_t size)
+{
+	const char *name = xattr_full_name(handler, suffix);
+	struct kernfs_node *kn = inode->i_private;
+
+	return kernfs_xattr_get(kn, name, value, size);
+}
+
+static int kernfs_vfs_xattr_set(const struct xattr_handler *handler,
+				struct mnt_idmap *idmap,
+				struct dentry *unused, struct inode *inode,
+				const char *suffix, const void *value,
+				size_t size, int flags)
+{
+	const char *name = xattr_full_name(handler, suffix);
+	struct kernfs_node *kn = inode->i_private;
+
+	return kernfs_xattr_set(kn, name, value, size, flags);
+}
+
+static int kernfs_vfs_user_xattr_set(const struct xattr_handler *handler,
+				     struct mnt_idmap *idmap,
+				     struct dentry *unused, struct inode *inode,
+				     const char *suffix, const void *value,
+				     size_t size, int flags)
+{
+	const char *full_name = xattr_full_name(handler, suffix);
+	struct kernfs_node *kn = inode->i_private;
+	struct kernfs_iattrs *attrs;
+
+	if (!(kernfs_root(kn)->flags & KERNFS_ROOT_SUPPORT_USER_XATTR))
+		return -EOPNOTSUPP;
+
+	attrs = kernfs_iattrs(kn);
+	if (!attrs)
+		return -ENOMEM;
+
+	/* See comment in kernfs_xattr_set() about locking. */
+	CLASS(kernfs_node_lock, lock)(kn);
+
+	return simple_xattr_set_limited(&kernfs_root(kn)->xa_cache,
+					&attrs->xattrs, &attrs->xattr_limits,
+					full_name, value, size, flags);
+}
+
+static const struct xattr_handler kernfs_trusted_xattr_handler = {
+	.prefix = XATTR_TRUSTED_PREFIX,
+	.get = kernfs_vfs_xattr_get,
+	.set = kernfs_vfs_xattr_set,
+};
+
+static const struct xattr_handler kernfs_security_xattr_handler = {
+	.prefix = XATTR_SECURITY_PREFIX,
+	.get = kernfs_vfs_xattr_get,
+	.set = kernfs_vfs_xattr_set,
+};
+
+static const struct xattr_handler kernfs_user_xattr_handler = {
+	.prefix = XATTR_USER_PREFIX,
+	.get = kernfs_vfs_xattr_get,
+	.set = kernfs_vfs_user_xattr_set,
+};
+
+const struct xattr_handler * const kernfs_xattr_handlers[] = {
+	&kernfs_trusted_xattr_handler,
+	&kernfs_security_xattr_handler,
+	&kernfs_user_xattr_handler,
+	NULL
+};