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, 307 insertions, 0 deletions

diff --git a/fs/btrfs/export.c b/fs/btrfs/export.c
new file mode 100644
index 000000000..230d9326b
--- /dev/null
+++ b/fs/btrfs/export.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/fs.h>
+#include <linux/types.h>
+#include "ctree.h"
+#include "disk-io.h"
+#include "btrfs_inode.h"
+#include "export.h"
+#include "accessors.h"
+#include "super.h"
+
+#define BTRFS_FID_SIZE_NON_CONNECTABLE (offsetof(struct btrfs_fid, \
+						 parent_objectid) / 4)
+#define BTRFS_FID_SIZE_CONNECTABLE (offsetof(struct btrfs_fid, \
+					     parent_root_objectid) / 4)
+#define BTRFS_FID_SIZE_CONNECTABLE_ROOT (sizeof(struct btrfs_fid) / 4)
+
+static int btrfs_encode_fh(struct inode *inode, u32 *fh, int *max_len,
+			   struct inode *parent)
+{
+	struct btrfs_fid *fid = (struct btrfs_fid *)fh;
+	int len = *max_len;
+	int type;
+
+	if (parent && (len < BTRFS_FID_SIZE_CONNECTABLE)) {
+		if (btrfs_root_id(BTRFS_I(inode)->root) !=
+		    btrfs_root_id(BTRFS_I(parent)->root))
+			*max_len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
+		else
+			*max_len = BTRFS_FID_SIZE_CONNECTABLE;
+		return FILEID_INVALID;
+	} else if (len < BTRFS_FID_SIZE_NON_CONNECTABLE) {
+		*max_len = BTRFS_FID_SIZE_NON_CONNECTABLE;
+		return FILEID_INVALID;
+	}
+
+	len  = BTRFS_FID_SIZE_NON_CONNECTABLE;
+	type = FILEID_BTRFS_WITHOUT_PARENT;
+
+	fid->objectid = btrfs_ino(BTRFS_I(inode));
+	fid->root_objectid = btrfs_root_id(BTRFS_I(inode)->root);
+	fid->gen = inode->i_generation;
+
+	if (parent) {
+		u64 parent_root_id;
+
+		fid->parent_objectid = btrfs_ino(BTRFS_I(parent));
+		fid->parent_gen = parent->i_generation;
+		parent_root_id = btrfs_root_id(BTRFS_I(parent)->root);
+
+		if (parent_root_id != fid->root_objectid) {
+			if (*max_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT)
+				return FILEID_INVALID;
+			fid->parent_root_objectid = parent_root_id;
+			len = BTRFS_FID_SIZE_CONNECTABLE_ROOT;
+			type = FILEID_BTRFS_WITH_PARENT_ROOT;
+		} else {
+			len = BTRFS_FID_SIZE_CONNECTABLE;
+			type = FILEID_BTRFS_WITH_PARENT;
+		}
+	}
+
+	*max_len = len;
+	return type;
+}
+
+/*
+ * Read dentry of inode with @objectid from filesystem root @root_objectid.
+ *
+ * @sb:             the filesystem super block
+ * @objectid:       inode objectid
+ * @root_objectid:  object id of the subvolume root where to look up the inode
+ * @generation:     optional, if not zero, verify that the found inode
+ *                  generation matches
+ *
+ * Return dentry alias for the inode, otherwise an error. In case the
+ * generation does not match return ESTALE.
+ */
+struct dentry *btrfs_get_dentry(struct super_block *sb, u64 objectid,
+				u64 root_objectid, u64 generation)
+{
+	struct btrfs_fs_info *fs_info = btrfs_sb(sb);
+	struct btrfs_root *root;
+	struct btrfs_inode *inode;
+
+	if (objectid < BTRFS_FIRST_FREE_OBJECTID)
+		return ERR_PTR(-ESTALE);
+
+	root = btrfs_get_fs_root(fs_info, root_objectid, true);
+	if (IS_ERR(root))
+		return ERR_CAST(root);
+
+	inode = btrfs_iget(objectid, root);
+	btrfs_put_root(root);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	if (generation != 0 && generation != inode->vfs_inode.i_generation) {
+		iput(&inode->vfs_inode);
+		return ERR_PTR(-ESTALE);
+	}
+
+	return d_obtain_alias(&inode->vfs_inode);
+}
+
+static struct dentry *btrfs_fh_to_parent(struct super_block *sb, struct fid *fh,
+					 int fh_len, int fh_type)
+{
+	struct btrfs_fid *fid = (struct btrfs_fid *) fh;
+	u64 objectid, root_objectid;
+	u32 generation;
+
+	if (fh_type == FILEID_BTRFS_WITH_PARENT) {
+		if (fh_len <  BTRFS_FID_SIZE_CONNECTABLE)
+			return NULL;
+		root_objectid = fid->root_objectid;
+	} else if (fh_type == FILEID_BTRFS_WITH_PARENT_ROOT) {
+		if (fh_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT)
+			return NULL;
+		root_objectid = fid->parent_root_objectid;
+	} else
+		return NULL;
+
+	objectid = fid->parent_objectid;
+	generation = fid->parent_gen;
+
+	return btrfs_get_dentry(sb, objectid, root_objectid, generation);
+}
+
+static struct dentry *btrfs_fh_to_dentry(struct super_block *sb, struct fid *fh,
+					 int fh_len, int fh_type)
+{
+	struct btrfs_fid *fid = (struct btrfs_fid *) fh;
+	u64 objectid, root_objectid;
+	u32 generation;
+
+	if ((fh_type != FILEID_BTRFS_WITH_PARENT ||
+	     fh_len < BTRFS_FID_SIZE_CONNECTABLE) &&
+	    (fh_type != FILEID_BTRFS_WITH_PARENT_ROOT ||
+	     fh_len < BTRFS_FID_SIZE_CONNECTABLE_ROOT) &&
+	    (fh_type != FILEID_BTRFS_WITHOUT_PARENT ||
+	     fh_len < BTRFS_FID_SIZE_NON_CONNECTABLE))
+		return NULL;
+
+	objectid = fid->objectid;
+	root_objectid = fid->root_objectid;
+	generation = fid->gen;
+
+	return btrfs_get_dentry(sb, objectid, root_objectid, generation);
+}
+
+struct dentry *btrfs_get_parent(struct dentry *child)
+{
+	struct btrfs_inode *dir = BTRFS_I(d_inode(child));
+	struct btrfs_inode *inode;
+	struct btrfs_root *root = dir->root;
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	struct btrfs_path *path;
+	struct extent_buffer *leaf;
+	struct btrfs_root_ref *ref;
+	struct btrfs_key key;
+	struct btrfs_key found_key;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return ERR_PTR(-ENOMEM);
+
+	if (btrfs_ino(dir) == BTRFS_FIRST_FREE_OBJECTID) {
+		key.objectid = btrfs_root_id(root);
+		key.type = BTRFS_ROOT_BACKREF_KEY;
+		key.offset = (u64)-1;
+		root = fs_info->tree_root;
+	} else {
+		key.objectid = btrfs_ino(dir);
+		key.type = BTRFS_INODE_REF_KEY;
+		key.offset = (u64)-1;
+	}
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0)
+		goto fail;
+	if (unlikely(ret == 0)) {
+		/*
+		 * Key with offset of -1 found, there would have to exist an
+		 * inode with such number or a root with such id.
+		 */
+		ret = -EUCLEAN;
+		goto fail;
+	}
+
+	if (path->slots[0] == 0) {
+		ret = -ENOENT;
+		goto fail;
+	}
+
+	path->slots[0]--;
+	leaf = path->nodes[0];
+
+	btrfs_item_key_to_cpu(leaf, &found_key, path->slots[0]);
+	if (found_key.objectid != key.objectid || found_key.type != key.type) {
+		ret = -ENOENT;
+		goto fail;
+	}
+
+	if (found_key.type == BTRFS_ROOT_BACKREF_KEY) {
+		ref = btrfs_item_ptr(leaf, path->slots[0],
+				     struct btrfs_root_ref);
+		key.objectid = btrfs_root_ref_dirid(leaf, ref);
+	} else {
+		key.objectid = found_key.offset;
+	}
+	btrfs_free_path(path);
+
+	if (found_key.type == BTRFS_ROOT_BACKREF_KEY) {
+		return btrfs_get_dentry(fs_info->sb, key.objectid,
+					found_key.offset, 0);
+	}
+
+	inode = btrfs_iget(key.objectid, root);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	return d_obtain_alias(&inode->vfs_inode);
+fail:
+	btrfs_free_path(path);
+	return ERR_PTR(ret);
+}
+
+static int btrfs_get_name(struct dentry *parent, char *name,
+			  struct dentry *child)
+{
+	struct btrfs_inode *inode = BTRFS_I(d_inode(child));
+	struct btrfs_inode *dir = BTRFS_I(d_inode(parent));
+	struct btrfs_root *root = dir->root;
+	struct btrfs_fs_info *fs_info = root->fs_info;
+	BTRFS_PATH_AUTO_FREE(path);
+	struct btrfs_inode_ref *iref;
+	struct btrfs_root_ref *rref;
+	struct extent_buffer *leaf;
+	unsigned long name_ptr;
+	struct btrfs_key key;
+	int name_len;
+	int ret;
+	u64 ino;
+
+	if (!S_ISDIR(dir->vfs_inode.i_mode))
+		return -EINVAL;
+
+	ino = btrfs_ino(inode);
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	if (ino == BTRFS_FIRST_FREE_OBJECTID) {
+		key.objectid = btrfs_root_id(inode->root);
+		key.type = BTRFS_ROOT_BACKREF_KEY;
+		key.offset = (u64)-1;
+		root = fs_info->tree_root;
+	} else {
+		key.objectid = ino;
+		key.type = BTRFS_INODE_REF_KEY;
+		key.offset = btrfs_ino(dir);
+	}
+
+	ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
+	if (ret < 0) {
+		return ret;
+	} else if (ret > 0) {
+		if (ino == BTRFS_FIRST_FREE_OBJECTID)
+			path->slots[0]--;
+		else
+			return -ENOENT;
+	}
+	leaf = path->nodes[0];
+
+	if (ino == BTRFS_FIRST_FREE_OBJECTID) {
+		rref = btrfs_item_ptr(leaf, path->slots[0],
+				     struct btrfs_root_ref);
+		name_ptr = (unsigned long)(rref + 1);
+		name_len = btrfs_root_ref_name_len(leaf, rref);
+	} else {
+		iref = btrfs_item_ptr(leaf, path->slots[0],
+				      struct btrfs_inode_ref);
+		name_ptr = (unsigned long)(iref + 1);
+		name_len = btrfs_inode_ref_name_len(leaf, iref);
+	}
+
+	read_extent_buffer(leaf, name, name_ptr, name_len);
+
+	/*
+	 * have to add the null termination to make sure that reconnect_path
+	 * gets the right len for strlen
+	 */
+	name[name_len] = '\0';
+
+	return 0;
+}
+
+const struct export_operations btrfs_export_ops = {
+	.encode_fh	= btrfs_encode_fh,
+	.fh_to_dentry	= btrfs_fh_to_dentry,
+	.fh_to_parent	= btrfs_fh_to_parent,
+	.get_parent	= btrfs_get_parent,
+	.get_name	= btrfs_get_name,
+};