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, 223 insertions, 0 deletions

diff --git a/fs/ufs/util.c b/fs/ufs/util.c
new file mode 100644
index 000000000..dff6f7461
--- /dev/null
+++ b/fs/ufs/util.c
@@ -0,0 +1,223 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/ufs/util.c
+ *
+ * Copyright (C) 1998
+ * Daniel Pirkl <daniel.pirkl@email.cz>
+ * Charles University, Faculty of Mathematics and Physics
+ */
+ 
+#include <linux/string.h>
+#include <linux/slab.h>
+#include <linux/buffer_head.h>
+
+#include "ufs_fs.h"
+#include "ufs.h"
+#include "swab.h"
+#include "util.h"
+
+struct ufs_buffer_head * _ubh_bread_ (struct ufs_sb_private_info * uspi,
+	struct super_block *sb, u64 fragment, u64 size)
+{
+	struct ufs_buffer_head * ubh;
+	unsigned i, j ;
+	u64  count = 0;
+	if (size & ~uspi->s_fmask)
+		return NULL;
+	count = size >> uspi->s_fshift;
+	if (count > UFS_MAXFRAG)
+		return NULL;
+	ubh = kmalloc_obj(struct ufs_buffer_head, GFP_NOFS);
+	if (!ubh)
+		return NULL;
+	ubh->fragment = fragment;
+	ubh->count = count;
+	for (i = 0; i < count; i++)
+		if (!(ubh->bh[i] = sb_bread(sb, fragment + i)))
+			goto failed;
+	for (; i < UFS_MAXFRAG; i++)
+		ubh->bh[i] = NULL;
+	return ubh;
+failed:
+	for (j = 0; j < i; j++)
+		brelse (ubh->bh[j]);
+	kfree(ubh);
+	return NULL;
+}
+
+struct ufs_buffer_head * ubh_bread_uspi (struct ufs_sb_private_info * uspi,
+	struct super_block *sb, u64 fragment, u64 size)
+{
+	unsigned i, j;
+	u64 count = 0;
+	if (size & ~uspi->s_fmask)
+		return NULL;
+	count = size >> uspi->s_fshift;
+	if (count <= 0 || count > UFS_MAXFRAG)
+		return NULL;
+	USPI_UBH(uspi)->fragment = fragment;
+	USPI_UBH(uspi)->count = count;
+	for (i = 0; i < count; i++)
+		if (!(USPI_UBH(uspi)->bh[i] = sb_bread(sb, fragment + i)))
+			goto failed;
+	for (; i < UFS_MAXFRAG; i++)
+		USPI_UBH(uspi)->bh[i] = NULL;
+	return USPI_UBH(uspi);
+failed:
+	for (j = 0; j < i; j++)
+		brelse (USPI_UBH(uspi)->bh[j]);
+	return NULL;
+}
+
+void ubh_brelse (struct ufs_buffer_head * ubh)
+{
+	unsigned i;
+	if (!ubh)
+		return;
+	for (i = 0; i < ubh->count; i++)
+		brelse (ubh->bh[i]);
+	kfree (ubh);
+}
+
+void ubh_brelse_uspi (struct ufs_sb_private_info * uspi)
+{
+	unsigned i;
+	if (!USPI_UBH(uspi))
+		return;
+	for ( i = 0; i < USPI_UBH(uspi)->count; i++ ) {
+		brelse (USPI_UBH(uspi)->bh[i]);
+		USPI_UBH(uspi)->bh[i] = NULL;
+	}
+}
+
+void ubh_mark_buffer_dirty (struct ufs_buffer_head * ubh)
+{
+	unsigned i;
+	if (!ubh)
+		return;
+	for ( i = 0; i < ubh->count; i++ )
+		mark_buffer_dirty (ubh->bh[i]);
+}
+
+void ubh_sync_block(struct ufs_buffer_head *ubh)
+{
+	if (ubh) {
+		unsigned i;
+
+		for (i = 0; i < ubh->count; i++)
+			write_dirty_buffer(ubh->bh[i], 0);
+
+		for (i = 0; i < ubh->count; i++)
+			wait_on_buffer(ubh->bh[i]);
+	}
+}
+
+void ubh_bforget (struct ufs_buffer_head * ubh)
+{
+	unsigned i;
+	if (!ubh) 
+		return;
+	for ( i = 0; i < ubh->count; i++ ) if ( ubh->bh[i] ) 
+		bforget (ubh->bh[i]);
+}
+ 
+int ubh_buffer_dirty (struct ufs_buffer_head * ubh)
+{
+	unsigned i;
+	unsigned result = 0;
+	if (!ubh)
+		return 0;
+	for ( i = 0; i < ubh->count; i++ )
+		result |= buffer_dirty(ubh->bh[i]);
+	return result;
+}
+
+dev_t
+ufs_get_inode_dev(struct super_block *sb, struct ufs_inode_info *ufsi)
+{
+	__u32 fs32;
+	dev_t dev;
+
+	if ((UFS_SB(sb)->s_flags & UFS_ST_MASK) == UFS_ST_SUNx86)
+		fs32 = fs32_to_cpu(sb, ufsi->i_u1.i_data[1]);
+	else
+		fs32 = fs32_to_cpu(sb, ufsi->i_u1.i_data[0]);
+	switch (UFS_SB(sb)->s_flags & UFS_ST_MASK) {
+	case UFS_ST_SUNx86:
+	case UFS_ST_SUN:
+		if ((fs32 & 0xffff0000) == 0 ||
+		    (fs32 & 0xffff0000) == 0xffff0000)
+			dev = old_decode_dev(fs32 & 0x7fff);
+		else
+			dev = MKDEV(sysv_major(fs32), sysv_minor(fs32));
+		break;
+
+	default:
+		dev = old_decode_dev(fs32);
+		break;
+	}
+	return dev;
+}
+
+void
+ufs_set_inode_dev(struct super_block *sb, struct ufs_inode_info *ufsi, dev_t dev)
+{
+	__u32 fs32;
+
+	switch (UFS_SB(sb)->s_flags & UFS_ST_MASK) {
+	case UFS_ST_SUNx86:
+	case UFS_ST_SUN:
+		fs32 = sysv_encode_dev(dev);
+		if ((fs32 & 0xffff8000) == 0) {
+			fs32 = old_encode_dev(dev);
+		}
+		break;
+
+	default:
+		fs32 = old_encode_dev(dev);
+		break;
+	}
+	if ((UFS_SB(sb)->s_flags & UFS_ST_MASK) == UFS_ST_SUNx86)
+		ufsi->i_u1.i_data[1] = cpu_to_fs32(sb, fs32);
+	else
+		ufsi->i_u1.i_data[0] = cpu_to_fs32(sb, fs32);
+}
+
+/**
+ * ufs_get_locked_folio() - locate, pin and lock a pagecache folio, if not exist
+ * read it from disk.
+ * @mapping: the address_space to search
+ * @index: the page index
+ *
+ * Locates the desired pagecache folio, if not exist we'll read it,
+ * locks it, increments its reference
+ * count and returns its address.
+ *
+ */
+struct folio *ufs_get_locked_folio(struct address_space *mapping,
+				 pgoff_t index)
+{
+	struct inode *inode = mapping->host;
+	struct folio *folio = filemap_lock_folio(mapping, index);
+	if (IS_ERR(folio)) {
+		folio = read_mapping_folio(mapping, index, NULL);
+
+		if (IS_ERR(folio)) {
+			printk(KERN_ERR "ufs_change_blocknr: read_mapping_folio error: ino %llu, index: %lu\n",
+			       mapping->host->i_ino, index);
+			return folio;
+		}
+
+		folio_lock(folio);
+
+		if (unlikely(folio->mapping == NULL)) {
+			/* Truncate got there first */
+			folio_unlock(folio);
+			folio_put(folio);
+			return NULL;
+		}
+	}
+	if (!folio_buffers(folio))
+		create_empty_buffers(folio, 1 << inode->i_blkbits, 0);
+	return folio;
+}