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, 434 insertions, 0 deletions

diff --git a/fs/ext2/namei.c b/fs/ext2/namei.c
new file mode 100644
index 000000000..8666233ec
--- /dev/null
+++ b/fs/ext2/namei.c
@@ -0,0 +1,434 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * linux/fs/ext2/namei.c
+ *
+ * Rewrite to pagecache. Almost all code had been changed, so blame me
+ * if the things go wrong. Please, send bug reports to
+ * viro@parcelfarce.linux.theplanet.co.uk
+ *
+ * Stuff here is basically a glue between the VFS and generic UNIXish
+ * filesystem that keeps everything in pagecache. All knowledge of the
+ * directory layout is in fs/ext2/dir.c - it turned out to be easily separatable
+ * and it's easier to debug that way. In principle we might want to
+ * generalize that a bit and turn it into a library. Or not.
+ *
+ * The only non-static object here is ext2_dir_inode_operations.
+ *
+ * Copyright (C) 1992, 1993, 1994, 1995
+ * Remy Card (card@masi.ibp.fr)
+ * Laboratoire MASI - Institut Blaise Pascal
+ * Universite Pierre et Marie Curie (Paris VI)
+ *
+ *  from
+ *
+ *  linux/fs/minix/namei.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ *
+ *  Big-endian to little-endian byte-swapping/bitmaps by
+ *        David S. Miller (davem@caip.rutgers.edu), 1995
+ */
+
+#include <linux/pagemap.h>
+#include <linux/quotaops.h>
+#include "ext2.h"
+#include "xattr.h"
+#include "acl.h"
+
+static inline int ext2_add_nondir(struct dentry *dentry, struct inode *inode)
+{
+	int err = ext2_add_link(dentry, inode);
+	if (!err) {
+		d_instantiate_new(dentry, inode);
+		return 0;
+	}
+	inode_dec_link_count(inode);
+	discard_new_inode(inode);
+	return err;
+}
+
+/*
+ * Methods themselves.
+ */
+
+static struct dentry *ext2_lookup(struct inode * dir, struct dentry *dentry, unsigned int flags)
+{
+	struct inode * inode;
+	ino_t ino;
+	int res;
+	
+	if (dentry->d_name.len > EXT2_NAME_LEN)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	res = ext2_inode_by_name(dir, &dentry->d_name, &ino);
+	if (res) {
+		if (res != -ENOENT)
+			return ERR_PTR(res);
+		inode = NULL;
+	} else {
+		inode = ext2_iget(dir->i_sb, ino);
+		if (inode == ERR_PTR(-ESTALE)) {
+			ext2_error(dir->i_sb, __func__,
+					"deleted inode referenced: %lu",
+					(unsigned long) ino);
+			return ERR_PTR(-EIO);
+		}
+	}
+	return d_splice_alias(inode, dentry);
+}
+
+struct dentry *ext2_get_parent(struct dentry *child)
+{
+	ino_t ino;
+	int res;
+
+	res = ext2_inode_by_name(d_inode(child), &dotdot_name, &ino);
+	if (res)
+		return ERR_PTR(res);
+
+	return d_obtain_alias(ext2_iget(child->d_sb, ino));
+} 
+
+/*
+ * By the time this is called, we already have created
+ * the directory cache entry for the new file, but it
+ * is so far negative - it has no inode.
+ *
+ * If the create succeeds, we fill in the inode information
+ * with d_instantiate(). 
+ */
+static int ext2_create (struct mnt_idmap * idmap,
+			struct inode * dir, struct dentry * dentry,
+			umode_t mode)
+{
+	struct inode *inode;
+	int err;
+
+	err = dquot_initialize(dir);
+	if (err)
+		return err;
+
+	inode = ext2_new_inode(dir, mode, &dentry->d_name);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	ext2_set_file_ops(inode);
+	mark_inode_dirty(inode);
+	return ext2_add_nondir(dentry, inode);
+}
+
+static int ext2_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
+			struct file *file, umode_t mode)
+{
+	struct inode *inode = ext2_new_inode(dir, mode, NULL);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	ext2_set_file_ops(inode);
+	mark_inode_dirty(inode);
+	d_tmpfile(file, inode);
+	unlock_new_inode(inode);
+	return finish_open_simple(file, 0);
+}
+
+static int ext2_mknod (struct mnt_idmap * idmap, struct inode * dir,
+	struct dentry *dentry, umode_t mode, dev_t rdev)
+{
+	struct inode * inode;
+	int err;
+
+	err = dquot_initialize(dir);
+	if (err)
+		return err;
+
+	inode = ext2_new_inode (dir, mode, &dentry->d_name);
+	err = PTR_ERR(inode);
+	if (!IS_ERR(inode)) {
+		init_special_inode(inode, inode->i_mode, rdev);
+		inode->i_op = &ext2_special_inode_operations;
+		mark_inode_dirty(inode);
+		err = ext2_add_nondir(dentry, inode);
+	}
+	return err;
+}
+
+static int ext2_symlink (struct mnt_idmap * idmap, struct inode * dir,
+	struct dentry * dentry, const char * symname)
+{
+	struct super_block * sb = dir->i_sb;
+	int err = -ENAMETOOLONG;
+	unsigned l = strlen(symname)+1;
+	struct inode * inode;
+
+	if (l > sb->s_blocksize)
+		goto out;
+
+	err = dquot_initialize(dir);
+	if (err)
+		goto out;
+
+	inode = ext2_new_inode (dir, S_IFLNK | S_IRWXUGO, &dentry->d_name);
+	err = PTR_ERR(inode);
+	if (IS_ERR(inode))
+		goto out;
+
+	if (l > sizeof (EXT2_I(inode)->i_data)) {
+		/* slow symlink */
+		inode->i_op = &ext2_symlink_inode_operations;
+		inode_nohighmem(inode);
+		inode->i_mapping->a_ops = &ext2_aops;
+		err = page_symlink(inode, symname, l);
+		if (err)
+			goto out_fail;
+	} else {
+		/* fast symlink */
+		inode->i_op = &ext2_fast_symlink_inode_operations;
+		inode->i_link = (char*)EXT2_I(inode)->i_data;
+		memcpy(inode->i_link, symname, l);
+		inode->i_size = l-1;
+	}
+	mark_inode_dirty(inode);
+
+	err = ext2_add_nondir(dentry, inode);
+out:
+	return err;
+
+out_fail:
+	inode_dec_link_count(inode);
+	discard_new_inode(inode);
+	goto out;
+}
+
+static int ext2_link (struct dentry * old_dentry, struct inode * dir,
+	struct dentry *dentry)
+{
+	struct inode *inode = d_inode(old_dentry);
+	int err;
+
+	err = dquot_initialize(dir);
+	if (err)
+		return err;
+
+	inode_set_ctime_current(inode);
+	inode_inc_link_count(inode);
+	ihold(inode);
+
+	err = ext2_add_link(dentry, inode);
+	if (!err) {
+		d_instantiate(dentry, inode);
+		return 0;
+	}
+	inode_dec_link_count(inode);
+	iput(inode);
+	return err;
+}
+
+static struct dentry *ext2_mkdir(struct mnt_idmap * idmap,
+				 struct inode * dir, struct dentry * dentry,
+				 umode_t mode)
+{
+	struct inode * inode;
+	int err;
+
+	err = dquot_initialize(dir);
+	if (err)
+		return ERR_PTR(err);
+
+	inode_inc_link_count(dir);
+
+	inode = ext2_new_inode(dir, mode, &dentry->d_name);
+	err = PTR_ERR(inode);
+	if (IS_ERR(inode))
+		goto out_dir;
+
+	inode->i_op = &ext2_dir_inode_operations;
+	inode->i_fop = &ext2_dir_operations;
+	inode->i_mapping->a_ops = &ext2_aops;
+
+	inode_inc_link_count(inode);
+
+	err = ext2_make_empty(inode, dir);
+	if (err)
+		goto out_fail;
+
+	err = ext2_add_link(dentry, inode);
+	if (err)
+		goto out_fail;
+
+	d_instantiate_new(dentry, inode);
+out:
+	return ERR_PTR(err);
+
+out_fail:
+	inode_dec_link_count(inode);
+	inode_dec_link_count(inode);
+	discard_new_inode(inode);
+out_dir:
+	inode_dec_link_count(dir);
+	goto out;
+}
+
+static int ext2_unlink(struct inode *dir, struct dentry *dentry)
+{
+	struct inode *inode = d_inode(dentry);
+	struct ext2_dir_entry_2 *de;
+	struct folio *folio;
+	int err;
+
+	err = dquot_initialize(dir);
+	if (err)
+		goto out;
+
+	de = ext2_find_entry(dir, &dentry->d_name, &folio);
+	if (IS_ERR(de)) {
+		err = PTR_ERR(de);
+		goto out;
+	}
+
+	err = ext2_delete_entry(de, folio);
+	folio_release_kmap(folio, de);
+	if (err)
+		goto out;
+
+	inode_set_ctime_to_ts(inode, inode_get_ctime(dir));
+
+	if (inode->i_nlink)
+		inode_dec_link_count(inode);
+
+	err = 0;
+out:
+	return err;
+}
+
+static int ext2_rmdir (struct inode * dir, struct dentry *dentry)
+{
+	struct inode * inode = d_inode(dentry);
+	int err = -ENOTEMPTY;
+
+	if (ext2_empty_dir(inode)) {
+		err = ext2_unlink(dir, dentry);
+		if (!err) {
+			inode->i_size = 0;
+			inode_dec_link_count(inode);
+			inode_dec_link_count(dir);
+		}
+	}
+	return err;
+}
+
+static int ext2_rename (struct mnt_idmap * idmap,
+			struct inode * old_dir, struct dentry * old_dentry,
+			struct inode * new_dir, struct dentry * new_dentry,
+			unsigned int flags)
+{
+	struct inode * old_inode = d_inode(old_dentry);
+	struct inode * new_inode = d_inode(new_dentry);
+	struct folio *dir_folio = NULL;
+	struct ext2_dir_entry_2 * dir_de = NULL;
+	struct folio * old_folio;
+	struct ext2_dir_entry_2 * old_de;
+	bool old_is_dir = S_ISDIR(old_inode->i_mode);
+	int err;
+
+	if (flags & ~RENAME_NOREPLACE)
+		return -EINVAL;
+
+	err = dquot_initialize(old_dir);
+	if (err)
+		return err;
+
+	err = dquot_initialize(new_dir);
+	if (err)
+		return err;
+
+	old_de = ext2_find_entry(old_dir, &old_dentry->d_name, &old_folio);
+	if (IS_ERR(old_de))
+		return PTR_ERR(old_de);
+
+	if (old_is_dir && old_dir != new_dir) {
+		err = -EIO;
+		dir_de = ext2_dotdot(old_inode, &dir_folio);
+		if (!dir_de)
+			goto out_old;
+	}
+
+	if (new_inode) {
+		struct folio *new_folio;
+		struct ext2_dir_entry_2 *new_de;
+
+		err = -ENOTEMPTY;
+		if (old_is_dir && !ext2_empty_dir(new_inode))
+			goto out_dir;
+
+		new_de = ext2_find_entry(new_dir, &new_dentry->d_name,
+					 &new_folio);
+		if (IS_ERR(new_de)) {
+			err = PTR_ERR(new_de);
+			goto out_dir;
+		}
+		err = ext2_set_link(new_dir, new_de, new_folio, old_inode, true);
+		folio_release_kmap(new_folio, new_de);
+		if (err)
+			goto out_dir;
+		inode_set_ctime_current(new_inode);
+		if (old_is_dir)
+			drop_nlink(new_inode);
+		inode_dec_link_count(new_inode);
+	} else {
+		err = ext2_add_link(new_dentry, old_inode);
+		if (err)
+			goto out_dir;
+		if (old_is_dir)
+			inode_inc_link_count(new_dir);
+	}
+
+	/*
+	 * Like most other Unix systems, set the ctime for inodes on a
+ 	 * rename.
+	 */
+	inode_set_ctime_current(old_inode);
+	mark_inode_dirty(old_inode);
+
+	err = ext2_delete_entry(old_de, old_folio);
+	if (!err && old_is_dir) {
+		if (old_dir != new_dir)
+			err = ext2_set_link(old_inode, dir_de, dir_folio,
+					    new_dir, false);
+
+		inode_dec_link_count(old_dir);
+	}
+out_dir:
+	if (dir_de)
+		folio_release_kmap(dir_folio, dir_de);
+out_old:
+	folio_release_kmap(old_folio, old_de);
+	return err;
+}
+
+const struct inode_operations ext2_dir_inode_operations = {
+	.create		= ext2_create,
+	.lookup		= ext2_lookup,
+	.link		= ext2_link,
+	.unlink		= ext2_unlink,
+	.symlink	= ext2_symlink,
+	.mkdir		= ext2_mkdir,
+	.rmdir		= ext2_rmdir,
+	.mknod		= ext2_mknod,
+	.rename		= ext2_rename,
+	.listxattr	= ext2_listxattr,
+	.getattr	= ext2_getattr,
+	.setattr	= ext2_setattr,
+	.get_inode_acl	= ext2_get_acl,
+	.set_acl	= ext2_set_acl,
+	.tmpfile	= ext2_tmpfile,
+	.fileattr_get	= ext2_fileattr_get,
+	.fileattr_set	= ext2_fileattr_set,
+};
+
+const struct inode_operations ext2_special_inode_operations = {
+	.listxattr	= ext2_listxattr,
+	.getattr	= ext2_getattr,
+	.setattr	= ext2_setattr,
+	.get_inode_acl	= ext2_get_acl,
+	.set_acl	= ext2_set_acl,
+};