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, 579 insertions, 0 deletions

diff --git a/fs/nilfs2/page.c b/fs/nilfs2/page.c
new file mode 100644
index 000000000..cf4f1c679
--- /dev/null
+++ b/fs/nilfs2/page.c
@@ -0,0 +1,579 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Buffer/page management specific to NILFS
+ *
+ * Copyright (C) 2005-2008 Nippon Telegraph and Telephone Corporation.
+ *
+ * Written by Ryusuke Konishi and Seiji Kihara.
+ */
+
+#include <linux/pagemap.h>
+#include <linux/writeback.h>
+#include <linux/swap.h>
+#include <linux/bitops.h>
+#include <linux/page-flags.h>
+#include <linux/list.h>
+#include <linux/highmem.h>
+#include <linux/folio_batch.h>
+#include <linux/gfp.h>
+#include "nilfs.h"
+#include "page.h"
+#include "mdt.h"
+
+
+#define NILFS_BUFFER_INHERENT_BITS					\
+	(BIT(BH_Uptodate) | BIT(BH_Mapped) | BIT(BH_NILFS_Node) |	\
+	 BIT(BH_NILFS_Volatile) | BIT(BH_NILFS_Checked))
+
+static struct buffer_head *__nilfs_get_folio_block(struct folio *folio,
+		unsigned long block, pgoff_t index, int blkbits,
+		unsigned long b_state)
+
+{
+	unsigned long first_block;
+	struct buffer_head *bh = folio_buffers(folio);
+
+	if (!bh)
+		bh = create_empty_buffers(folio, 1 << blkbits, b_state);
+
+	first_block = (unsigned long)index << (PAGE_SHIFT - blkbits);
+	bh = get_nth_bh(bh, block - first_block);
+
+	wait_on_buffer(bh);
+	return bh;
+}
+
+struct buffer_head *nilfs_grab_buffer(struct inode *inode,
+				      struct address_space *mapping,
+				      unsigned long blkoff,
+				      unsigned long b_state)
+{
+	int blkbits = inode->i_blkbits;
+	pgoff_t index = blkoff >> (PAGE_SHIFT - blkbits);
+	struct folio *folio;
+	struct buffer_head *bh;
+
+	folio = filemap_grab_folio(mapping, index);
+	if (IS_ERR(folio))
+		return NULL;
+
+	bh = __nilfs_get_folio_block(folio, blkoff, index, blkbits, b_state);
+	if (unlikely(!bh)) {
+		folio_unlock(folio);
+		folio_put(folio);
+		return NULL;
+	}
+	bh->b_bdev = inode->i_sb->s_bdev;
+	return bh;
+}
+
+/**
+ * nilfs_forget_buffer - discard dirty state
+ * @bh: buffer head of the buffer to be discarded
+ */
+void nilfs_forget_buffer(struct buffer_head *bh)
+{
+	struct folio *folio = bh->b_folio;
+	const unsigned long clear_bits =
+		(BIT(BH_Uptodate) | BIT(BH_Dirty) | BIT(BH_Mapped) |
+		 BIT(BH_Async_Write) | BIT(BH_NILFS_Volatile) |
+		 BIT(BH_NILFS_Checked) | BIT(BH_NILFS_Redirected) |
+		 BIT(BH_Delay));
+
+	lock_buffer(bh);
+	set_mask_bits(&bh->b_state, clear_bits, 0);
+	if (nilfs_folio_buffers_clean(folio))
+		__nilfs_clear_folio_dirty(folio);
+
+	bh->b_blocknr = -1;
+	folio_clear_uptodate(folio);
+	folio_clear_mappedtodisk(folio);
+	unlock_buffer(bh);
+	brelse(bh);
+}
+
+/**
+ * nilfs_copy_buffer -- copy buffer data and flags
+ * @dbh: destination buffer
+ * @sbh: source buffer
+ */
+void nilfs_copy_buffer(struct buffer_head *dbh, struct buffer_head *sbh)
+{
+	void *saddr, *daddr;
+	unsigned long bits;
+	struct folio *sfolio = sbh->b_folio, *dfolio = dbh->b_folio;
+	struct buffer_head *bh;
+
+	saddr = kmap_local_folio(sfolio, bh_offset(sbh));
+	daddr = kmap_local_folio(dfolio, bh_offset(dbh));
+	memcpy(daddr, saddr, sbh->b_size);
+	kunmap_local(daddr);
+	kunmap_local(saddr);
+
+	dbh->b_state = sbh->b_state & NILFS_BUFFER_INHERENT_BITS;
+	dbh->b_blocknr = sbh->b_blocknr;
+	dbh->b_bdev = sbh->b_bdev;
+
+	bh = dbh;
+	bits = sbh->b_state & (BIT(BH_Uptodate) | BIT(BH_Mapped));
+	while ((bh = bh->b_this_page) != dbh) {
+		lock_buffer(bh);
+		bits &= bh->b_state;
+		unlock_buffer(bh);
+	}
+	if (bits & BIT(BH_Uptodate))
+		folio_mark_uptodate(dfolio);
+	else
+		folio_clear_uptodate(dfolio);
+	if (bits & BIT(BH_Mapped))
+		folio_set_mappedtodisk(dfolio);
+	else
+		folio_clear_mappedtodisk(dfolio);
+}
+
+/**
+ * nilfs_folio_buffers_clean - Check if a folio has dirty buffers or not.
+ * @folio: Folio to be checked.
+ *
+ * Return: false if the folio has dirty buffers, true otherwise.
+ */
+bool nilfs_folio_buffers_clean(struct folio *folio)
+{
+	struct buffer_head *bh, *head;
+
+	bh = head = folio_buffers(folio);
+	do {
+		if (buffer_dirty(bh))
+			return false;
+		bh = bh->b_this_page;
+	} while (bh != head);
+	return true;
+}
+
+void nilfs_folio_bug(struct folio *folio)
+{
+	struct buffer_head *bh, *head;
+	struct address_space *m;
+	u64 ino;
+
+	if (unlikely(!folio)) {
+		printk(KERN_CRIT "NILFS_FOLIO_BUG(NULL)\n");
+		return;
+	}
+
+	m = folio->mapping;
+	ino = m ? m->host->i_ino : 0;
+
+	printk(KERN_CRIT "NILFS_FOLIO_BUG(%p): cnt=%d index#=%lu flags=0x%lx  mapping=%p ino=%llu\n",
+		folio, folio_ref_count(folio), folio->index, folio->flags.f,
+		m, ino);
+
+	head = folio_buffers(folio);
+	if (head) {
+		int i = 0;
+
+		bh = head;
+		do {
+			printk(KERN_CRIT
+			       " BH[%d] %p: cnt=%d block#=%llu state=0x%lx\n",
+			       i++, bh, atomic_read(&bh->b_count),
+			       (unsigned long long)bh->b_blocknr, bh->b_state);
+			bh = bh->b_this_page;
+		} while (bh != head);
+	}
+}
+
+/**
+ * nilfs_copy_folio -- copy the folio with buffers
+ * @dst: destination folio
+ * @src: source folio
+ * @copy_dirty: flag whether to copy dirty states on the folio's buffer heads.
+ *
+ * This function is for both data folios and btnode folios.  The dirty flag
+ * should be treated by caller.  The folio must not be under i/o.
+ * Both src and dst folio must be locked
+ */
+static void nilfs_copy_folio(struct folio *dst, struct folio *src,
+		bool copy_dirty)
+{
+	struct buffer_head *dbh, *dbufs, *sbh;
+	unsigned long mask = NILFS_BUFFER_INHERENT_BITS;
+
+	BUG_ON(folio_test_writeback(dst));
+
+	sbh = folio_buffers(src);
+	dbh = folio_buffers(dst);
+	if (!dbh)
+		dbh = create_empty_buffers(dst, sbh->b_size, 0);
+
+	if (copy_dirty)
+		mask |= BIT(BH_Dirty);
+
+	dbufs = dbh;
+	do {
+		lock_buffer(sbh);
+		lock_buffer(dbh);
+		dbh->b_state = sbh->b_state & mask;
+		dbh->b_blocknr = sbh->b_blocknr;
+		dbh->b_bdev = sbh->b_bdev;
+		sbh = sbh->b_this_page;
+		dbh = dbh->b_this_page;
+	} while (dbh != dbufs);
+
+	folio_copy(dst, src);
+
+	if (folio_test_uptodate(src) && !folio_test_uptodate(dst))
+		folio_mark_uptodate(dst);
+	else if (!folio_test_uptodate(src) && folio_test_uptodate(dst))
+		folio_clear_uptodate(dst);
+	if (folio_test_mappedtodisk(src) && !folio_test_mappedtodisk(dst))
+		folio_set_mappedtodisk(dst);
+	else if (!folio_test_mappedtodisk(src) && folio_test_mappedtodisk(dst))
+		folio_clear_mappedtodisk(dst);
+
+	do {
+		unlock_buffer(sbh);
+		unlock_buffer(dbh);
+		sbh = sbh->b_this_page;
+		dbh = dbh->b_this_page;
+	} while (dbh != dbufs);
+}
+
+int nilfs_copy_dirty_pages(struct address_space *dmap,
+			   struct address_space *smap)
+{
+	struct inode *smap_inode = smap->host;
+	struct folio_batch fbatch;
+	unsigned int i;
+	pgoff_t index = 0;
+	int err = 0;
+
+	folio_batch_init(&fbatch);
+repeat:
+	if (!filemap_get_folios_tag(smap, &index, (pgoff_t)-1,
+				PAGECACHE_TAG_DIRTY, &fbatch))
+		return 0;
+
+	for (i = 0; i < folio_batch_count(&fbatch); i++) {
+		struct folio *folio = fbatch.folios[i], *dfolio;
+
+		folio_lock(folio);
+		if (unlikely(!folio_test_dirty(folio))) {
+			if (WARN_ONCE(!sb_rdonly(smap_inode->i_sb),
+					"inconsistent dirty state\n"))
+				goto unlock_folio;
+
+			/*
+			 * If the filesystem has been forced to read-only
+			 * due to metadata corruption.
+			 */
+			folio_unlock(folio);
+			err = -EROFS;
+			break;
+		}
+
+		dfolio = filemap_grab_folio(dmap, folio->index);
+		if (IS_ERR(dfolio)) {
+			/* No empty page is added to the page cache */
+			folio_unlock(folio);
+			err = PTR_ERR(dfolio);
+			break;
+		}
+		if (unlikely(!folio_buffers(folio)))
+			NILFS_FOLIO_BUG(folio,
+				       "found empty page in dat page cache");
+
+		nilfs_copy_folio(dfolio, folio, true);
+		filemap_dirty_folio(folio_mapping(dfolio), dfolio);
+
+		folio_unlock(dfolio);
+		folio_put(dfolio);
+unlock_folio:
+		folio_unlock(folio);
+	}
+	folio_batch_release(&fbatch);
+	cond_resched();
+
+	if (likely(!err))
+		goto repeat;
+	return err;
+}
+
+/**
+ * nilfs_copy_back_pages -- copy back pages to original cache from shadow cache
+ * @dmap: destination page cache
+ * @smap: source page cache
+ *
+ * No pages must be added to the cache during this process.
+ * This must be ensured by the caller.
+ */
+void nilfs_copy_back_pages(struct address_space *dmap,
+			   struct address_space *smap)
+{
+	struct folio_batch fbatch;
+	unsigned int i, n;
+	pgoff_t start = 0;
+
+	folio_batch_init(&fbatch);
+repeat:
+	n = filemap_get_folios(smap, &start, ~0UL, &fbatch);
+	if (!n)
+		return;
+
+	for (i = 0; i < folio_batch_count(&fbatch); i++) {
+		struct folio *folio = fbatch.folios[i], *dfolio;
+		pgoff_t index = folio->index;
+
+		folio_lock(folio);
+		dfolio = filemap_lock_folio(dmap, index);
+		if (!IS_ERR(dfolio)) {
+			/* overwrite existing folio in the destination cache */
+			WARN_ON(folio_test_dirty(dfolio));
+			nilfs_copy_folio(dfolio, folio, false);
+			folio_unlock(dfolio);
+			folio_put(dfolio);
+			/* Do we not need to remove folio from smap here? */
+		} else {
+			struct folio *f;
+
+			/* move the folio to the destination cache */
+			xa_lock_irq(&smap->i_pages);
+			f = __xa_erase(&smap->i_pages, index);
+			WARN_ON(folio != f);
+			smap->nrpages--;
+			xa_unlock_irq(&smap->i_pages);
+
+			xa_lock_irq(&dmap->i_pages);
+			f = __xa_store(&dmap->i_pages, index, folio, GFP_NOFS);
+			if (unlikely(f)) {
+				/* Probably -ENOMEM */
+				folio->mapping = NULL;
+				folio_put(folio);
+			} else {
+				folio->mapping = dmap;
+				dmap->nrpages++;
+				if (folio_test_dirty(folio))
+					__xa_set_mark(&dmap->i_pages, index,
+							PAGECACHE_TAG_DIRTY);
+			}
+			xa_unlock_irq(&dmap->i_pages);
+		}
+		folio_unlock(folio);
+	}
+	folio_batch_release(&fbatch);
+	cond_resched();
+
+	goto repeat;
+}
+
+/**
+ * nilfs_clear_dirty_pages - discard dirty pages in address space
+ * @mapping: address space with dirty pages for discarding
+ */
+void nilfs_clear_dirty_pages(struct address_space *mapping)
+{
+	struct folio_batch fbatch;
+	unsigned int i;
+	pgoff_t index = 0;
+
+	folio_batch_init(&fbatch);
+
+	while (filemap_get_folios_tag(mapping, &index, (pgoff_t)-1,
+				PAGECACHE_TAG_DIRTY, &fbatch)) {
+		for (i = 0; i < folio_batch_count(&fbatch); i++) {
+			struct folio *folio = fbatch.folios[i];
+
+			folio_lock(folio);
+
+			/*
+			 * This folio may have been removed from the address
+			 * space by truncation or invalidation when the lock
+			 * was acquired.  Skip processing in that case.
+			 */
+			if (likely(folio->mapping == mapping))
+				nilfs_clear_folio_dirty(folio);
+
+			folio_unlock(folio);
+		}
+		folio_batch_release(&fbatch);
+		cond_resched();
+	}
+}
+
+/**
+ * nilfs_clear_folio_dirty - discard dirty folio
+ * @folio: dirty folio that will be discarded
+ *
+ * nilfs_clear_folio_dirty() clears working states including dirty state for
+ * the folio and its buffers.  If the folio has buffers, clear only if it is
+ * confirmed that none of the buffer heads are busy (none have valid
+ * references and none are locked).
+ */
+void nilfs_clear_folio_dirty(struct folio *folio)
+{
+	struct buffer_head *bh, *head;
+
+	BUG_ON(!folio_test_locked(folio));
+
+	head = folio_buffers(folio);
+	if (head) {
+		const unsigned long clear_bits =
+			(BIT(BH_Uptodate) | BIT(BH_Dirty) | BIT(BH_Mapped) |
+			 BIT(BH_Async_Write) | BIT(BH_NILFS_Volatile) |
+			 BIT(BH_NILFS_Checked) | BIT(BH_NILFS_Redirected) |
+			 BIT(BH_Delay));
+		bool busy, invalidated = false;
+
+recheck_buffers:
+		busy = false;
+		bh = head;
+		do {
+			if (atomic_read(&bh->b_count) | buffer_locked(bh)) {
+				busy = true;
+				break;
+			}
+		} while (bh = bh->b_this_page, bh != head);
+
+		if (busy) {
+			if (invalidated)
+				return;
+			invalidate_bh_lrus();
+			invalidated = true;
+			goto recheck_buffers;
+		}
+
+		bh = head;
+		do {
+			lock_buffer(bh);
+			set_mask_bits(&bh->b_state, clear_bits, 0);
+			unlock_buffer(bh);
+		} while (bh = bh->b_this_page, bh != head);
+	}
+
+	folio_clear_uptodate(folio);
+	folio_clear_mappedtodisk(folio);
+	folio_clear_checked(folio);
+	__nilfs_clear_folio_dirty(folio);
+}
+
+unsigned int nilfs_page_count_clean_buffers(struct folio *folio,
+					    unsigned int from, unsigned int to)
+{
+	unsigned int block_start, block_end;
+	struct buffer_head *bh, *head;
+	unsigned int nc = 0;
+
+	for (bh = head = folio_buffers(folio), block_start = 0;
+	     bh != head || !block_start;
+	     block_start = block_end, bh = bh->b_this_page) {
+		block_end = block_start + bh->b_size;
+		if (block_end > from && block_start < to && !buffer_dirty(bh))
+			nc++;
+	}
+	return nc;
+}
+
+/*
+ * NILFS2 needs clear_page_dirty() in the following two cases:
+ *
+ * 1) For B-tree node pages and data pages of DAT file, NILFS2 clears dirty
+ *    flag of pages when it copies back pages from shadow cache to the
+ *    original cache.
+ *
+ * 2) Some B-tree operations like insertion or deletion may dispose buffers
+ *    in dirty state, and this needs to cancel the dirty state of their pages.
+ */
+void __nilfs_clear_folio_dirty(struct folio *folio)
+{
+	struct address_space *mapping = folio->mapping;
+
+	if (mapping) {
+		xa_lock_irq(&mapping->i_pages);
+		if (folio_test_dirty(folio)) {
+			__xa_clear_mark(&mapping->i_pages, folio->index,
+					     PAGECACHE_TAG_DIRTY);
+			xa_unlock_irq(&mapping->i_pages);
+			folio_clear_dirty_for_io(folio);
+			return;
+		}
+		xa_unlock_irq(&mapping->i_pages);
+		return;
+	}
+	folio_clear_dirty(folio);
+}
+
+/**
+ * nilfs_find_uncommitted_extent - find extent of uncommitted data
+ * @inode: inode
+ * @start_blk: start block offset (in)
+ * @blkoff: start offset of the found extent (out)
+ *
+ * This function searches an extent of buffers marked "delayed" which
+ * starts from a block offset equal to or larger than @start_blk.  If
+ * such an extent was found, this will store the start offset in
+ * @blkoff and return its length in blocks.
+ *
+ * Return: Length in blocks of found extent, 0 otherwise.
+ */
+unsigned long nilfs_find_uncommitted_extent(struct inode *inode,
+					    sector_t start_blk,
+					    sector_t *blkoff)
+{
+	unsigned int i, nr_folios;
+	pgoff_t index;
+	unsigned long length = 0;
+	struct folio_batch fbatch;
+	struct folio *folio;
+
+	if (inode->i_mapping->nrpages == 0)
+		return 0;
+
+	index = start_blk >> (PAGE_SHIFT - inode->i_blkbits);
+
+	folio_batch_init(&fbatch);
+
+repeat:
+	nr_folios = filemap_get_folios_contig(inode->i_mapping, &index, ULONG_MAX,
+			&fbatch);
+	if (nr_folios == 0)
+		return length;
+
+	i = 0;
+	do {
+		folio = fbatch.folios[i];
+
+		folio_lock(folio);
+		if (folio_buffers(folio)) {
+			struct buffer_head *bh, *head;
+			sector_t b;
+
+			b = folio->index << (PAGE_SHIFT - inode->i_blkbits);
+			bh = head = folio_buffers(folio);
+			do {
+				if (b < start_blk)
+					continue;
+				if (buffer_delay(bh)) {
+					if (length == 0)
+						*blkoff = b;
+					length++;
+				} else if (length > 0) {
+					goto out_locked;
+				}
+			} while (++b, bh = bh->b_this_page, bh != head);
+		} else {
+			if (length > 0)
+				goto out_locked;
+		}
+		folio_unlock(folio);
+
+	} while (++i < nr_folios);
+
+	folio_batch_release(&fbatch);
+	cond_resched();
+	goto repeat;
+
+out_locked:
+	folio_unlock(folio);
+	folio_batch_release(&fbatch);
+	return length;
+}