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, 158 insertions, 0 deletions

diff --git a/fs/jfs/file.c b/fs/jfs/file.c
new file mode 100644
index 000000000..246568cb9
--- /dev/null
+++ b/fs/jfs/file.c
@@ -0,0 +1,158 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) International Business Machines Corp., 2000-2002
+ *   Portions Copyright (C) Christoph Hellwig, 2001-2002
+ */
+
+#include <linux/mm.h>
+#include <linux/fs.h>
+#include <linux/filelock.h>
+#include <linux/posix_acl.h>
+#include <linux/quotaops.h>
+#include "jfs_incore.h"
+#include "jfs_inode.h"
+#include "jfs_dmap.h"
+#include "jfs_txnmgr.h"
+#include "jfs_xattr.h"
+#include "jfs_acl.h"
+#include "jfs_debug.h"
+
+int jfs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
+{
+	struct inode *inode = file->f_mapping->host;
+	int rc = 0;
+
+	rc = file_write_and_wait_range(file, start, end);
+	if (rc)
+		return rc;
+
+	inode_lock(inode);
+	if (!(inode_state_read_once(inode) & I_DIRTY_ALL) ||
+	    (datasync && !(inode_state_read_once(inode) & I_DIRTY_DATASYNC))) {
+		/* Make sure committed changes hit the disk */
+		jfs_flush_journal(JFS_SBI(inode->i_sb)->log, 1);
+		inode_unlock(inode);
+		return rc;
+	}
+
+	rc |= jfs_commit_inode(inode, 1);
+	inode_unlock(inode);
+
+	return rc ? -EIO : 0;
+}
+
+static int jfs_open(struct inode *inode, struct file *file)
+{
+	int rc;
+
+	if (S_ISREG(inode->i_mode) && inode->i_size < 0)
+		return -EIO;
+
+	if ((rc = dquot_file_open(inode, file)))
+		return rc;
+
+	/*
+	 * We attempt to allow only one "active" file open per aggregate
+	 * group.  Otherwise, appending to files in parallel can cause
+	 * fragmentation within the files.
+	 *
+	 * If the file is empty, it was probably just created and going
+	 * to be written to.  If it has a size, we'll hold off until the
+	 * file is actually grown.
+	 */
+	if (S_ISREG(inode->i_mode) && file->f_mode & FMODE_WRITE &&
+	    (inode->i_size == 0)) {
+		struct jfs_inode_info *ji = JFS_IP(inode);
+		spin_lock_irq(&ji->ag_lock);
+		if (ji->active_ag == -1) {
+			struct jfs_sb_info *jfs_sb = JFS_SBI(inode->i_sb);
+			ji->active_ag = BLKTOAG(addressPXD(&ji->ixpxd), jfs_sb);
+			atomic_inc(&jfs_sb->bmap->db_active[ji->active_ag]);
+		}
+		spin_unlock_irq(&ji->ag_lock);
+	}
+
+	return 0;
+}
+static int jfs_release(struct inode *inode, struct file *file)
+{
+	struct jfs_inode_info *ji = JFS_IP(inode);
+
+	spin_lock_irq(&ji->ag_lock);
+	if (ji->active_ag != -1) {
+		struct bmap *bmap = JFS_SBI(inode->i_sb)->bmap;
+		atomic_dec(&bmap->db_active[ji->active_ag]);
+		ji->active_ag = -1;
+	}
+	spin_unlock_irq(&ji->ag_lock);
+
+	return 0;
+}
+
+int jfs_setattr(struct mnt_idmap *idmap, struct dentry *dentry,
+		struct iattr *iattr)
+{
+	struct inode *inode = d_inode(dentry);
+	int rc;
+
+	rc = setattr_prepare(&nop_mnt_idmap, dentry, iattr);
+	if (rc)
+		return rc;
+
+	if (is_quota_modification(&nop_mnt_idmap, inode, iattr)) {
+		rc = dquot_initialize(inode);
+		if (rc)
+			return rc;
+	}
+	if ((iattr->ia_valid & ATTR_UID && !uid_eq(iattr->ia_uid, inode->i_uid)) ||
+	    (iattr->ia_valid & ATTR_GID && !gid_eq(iattr->ia_gid, inode->i_gid))) {
+		rc = dquot_transfer(&nop_mnt_idmap, inode, iattr);
+		if (rc)
+			return rc;
+	}
+
+	if ((iattr->ia_valid & ATTR_SIZE) &&
+	    iattr->ia_size != i_size_read(inode)) {
+		inode_dio_wait(inode);
+
+		rc = inode_newsize_ok(inode, iattr->ia_size);
+		if (rc)
+			return rc;
+
+		truncate_setsize(inode, iattr->ia_size);
+		jfs_truncate(inode);
+	}
+
+	setattr_copy(&nop_mnt_idmap, inode, iattr);
+	mark_inode_dirty(inode);
+
+	if (iattr->ia_valid & ATTR_MODE)
+		rc = posix_acl_chmod(&nop_mnt_idmap, dentry, inode->i_mode);
+	return rc;
+}
+
+const struct inode_operations jfs_file_inode_operations = {
+	.listxattr	= jfs_listxattr,
+	.setattr	= jfs_setattr,
+	.fileattr_get	= jfs_fileattr_get,
+	.fileattr_set	= jfs_fileattr_set,
+#ifdef CONFIG_JFS_POSIX_ACL
+	.get_inode_acl	= jfs_get_acl,
+	.set_acl	= jfs_set_acl,
+#endif
+};
+
+const struct file_operations jfs_file_operations = {
+	.open		= jfs_open,
+	.llseek		= generic_file_llseek,
+	.read_iter	= generic_file_read_iter,
+	.write_iter	= generic_file_write_iter,
+	.mmap_prepare	= generic_file_mmap_prepare,
+	.splice_read	= filemap_splice_read,
+	.splice_write	= iter_file_splice_write,
+	.fsync		= jfs_fsync,
+	.release	= jfs_release,
+	.unlocked_ioctl = jfs_ioctl,
+	.compat_ioctl	= compat_ptr_ioctl,
+	.setlease	= generic_setlease,
+};