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, 165 insertions, 0 deletions

diff --git a/fs/nilfs2/file.c b/fs/nilfs2/file.c
new file mode 100644
index 000000000..f93b68c48
--- /dev/null
+++ b/fs/nilfs2/file.c
@@ -0,0 +1,165 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * NILFS regular file handling primitives including fsync().
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * Written by Amagai Yoshiji and Ryusuke Konishi.
+ */
+
+#include <linux/fs.h>
+#include <linux/filelock.h>
+#include <linux/mm.h>
+#include <linux/writeback.h>
+#include "nilfs.h"
+#include "segment.h"
+
+int nilfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync)
+{
+	/*
+	 * Called from fsync() system call
+	 * This is the only entry point that can catch write and synch
+	 * timing for both data blocks and intermediate blocks.
+	 *
+	 * This function should be implemented when the writeback function
+	 * will be implemented.
+	 */
+	struct the_nilfs *nilfs;
+	struct inode *inode = file->f_mapping->host;
+	int err = 0;
+
+	if (nilfs_inode_dirty(inode)) {
+		if (datasync)
+			err = nilfs_construct_dsync_segment(inode->i_sb, inode,
+							    start, end);
+		else
+			err = nilfs_construct_segment(inode->i_sb);
+	}
+
+	nilfs = inode->i_sb->s_fs_info;
+	if (!err)
+		err = nilfs_flush_device(nilfs);
+
+	return err;
+}
+
+static vm_fault_t nilfs_page_mkwrite(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct folio *folio = page_folio(vmf->page);
+	struct inode *inode = file_inode(vma->vm_file);
+	struct nilfs_transaction_info ti;
+	struct buffer_head *bh, *head;
+	int ret = 0;
+
+	if (unlikely(nilfs_near_disk_full(inode->i_sb->s_fs_info)))
+		return VM_FAULT_SIGBUS; /* -ENOSPC */
+
+	sb_start_pagefault(inode->i_sb);
+	folio_lock(folio);
+	if (folio->mapping != inode->i_mapping ||
+	    folio_pos(folio) >= i_size_read(inode) ||
+	    !folio_test_uptodate(folio)) {
+		folio_unlock(folio);
+		ret = -EFAULT;	/* make the VM retry the fault */
+		goto out;
+	}
+
+	/*
+	 * check to see if the folio is mapped already (no holes)
+	 */
+	if (folio_test_mappedtodisk(folio))
+		goto mapped;
+
+	head = folio_buffers(folio);
+	if (head) {
+		int fully_mapped = 1;
+
+		bh = head;
+		do {
+			if (!buffer_mapped(bh)) {
+				fully_mapped = 0;
+				break;
+			}
+		} while (bh = bh->b_this_page, bh != head);
+
+		if (fully_mapped) {
+			folio_set_mappedtodisk(folio);
+			goto mapped;
+		}
+	}
+	folio_unlock(folio);
+
+	/*
+	 * fill hole blocks
+	 */
+	ret = nilfs_transaction_begin(inode->i_sb, &ti, 1);
+	/* never returns -ENOMEM, but may return -ENOSPC */
+	if (unlikely(ret))
+		goto out;
+
+	file_update_time(vma->vm_file);
+	ret = block_page_mkwrite(vma, vmf, nilfs_get_block);
+	if (ret) {
+		nilfs_transaction_abort(inode->i_sb);
+		goto out;
+	}
+	nilfs_set_file_dirty(inode, 1 << (PAGE_SHIFT - inode->i_blkbits));
+	nilfs_transaction_commit(inode->i_sb);
+
+ mapped:
+	/*
+	 * Since checksumming including data blocks is performed to determine
+	 * the validity of the log to be written and used for recovery, it is
+	 * necessary to wait for writeback to finish here, regardless of the
+	 * stable write requirement of the backing device.
+	 */
+	folio_wait_writeback(folio);
+ out:
+	sb_end_pagefault(inode->i_sb);
+	return vmf_fs_error(ret);
+}
+
+static const struct vm_operations_struct nilfs_file_vm_ops = {
+	.fault		= filemap_fault,
+	.map_pages	= filemap_map_pages,
+	.page_mkwrite	= nilfs_page_mkwrite,
+};
+
+static int nilfs_file_mmap_prepare(struct vm_area_desc *desc)
+{
+	file_accessed(desc->file);
+	desc->vm_ops = &nilfs_file_vm_ops;
+	return 0;
+}
+
+/*
+ * We have mostly NULL's here: the current defaults are ok for
+ * the nilfs filesystem.
+ */
+const struct file_operations nilfs_file_operations = {
+	.llseek		= generic_file_llseek,
+	.read_iter	= generic_file_read_iter,
+	.write_iter	= generic_file_write_iter,
+	.unlocked_ioctl	= nilfs_ioctl,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	= nilfs_compat_ioctl,
+#endif	/* CONFIG_COMPAT */
+	.mmap_prepare	= nilfs_file_mmap_prepare,
+	.open		= generic_file_open,
+	/* .release	= nilfs_release_file, */
+	.fsync		= nilfs_sync_file,
+	.splice_read	= filemap_splice_read,
+	.splice_write   = iter_file_splice_write,
+	.setlease	= generic_setlease,
+};
+
+const struct inode_operations nilfs_file_inode_operations = {
+	.setattr	= nilfs_setattr,
+	.permission     = nilfs_permission,
+	.fiemap		= nilfs_fiemap,
+	.fileattr_get	= nilfs_fileattr_get,
+	.fileattr_set	= nilfs_fileattr_set,
+};
+
+/* end of file */