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, 180 insertions, 0 deletions

diff --git a/fs/affs/dir.c b/fs/affs/dir.c
new file mode 100644
index 000000000..d2b897ebb
--- /dev/null
+++ b/fs/affs/dir.c
@@ -0,0 +1,180 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/affs/dir.c
+ *
+ *  (c) 1996  Hans-Joachim Widmaier - Rewritten
+ *
+ *  (C) 1993  Ray Burr - Modified for Amiga FFS filesystem.
+ *
+ *  (C) 1992  Eric Youngdale Modified for ISO 9660 filesystem.
+ *
+ *  (C) 1991  Linus Torvalds - minix filesystem
+ *
+ *  affs directory handling functions
+ *
+ */
+
+#include <linux/iversion.h>
+#include <linux/filelock.h>
+#include "affs.h"
+
+struct affs_dir_data {
+	unsigned long ino;
+	u64 cookie;
+};
+
+static int affs_readdir(struct file *, struct dir_context *);
+
+static loff_t affs_dir_llseek(struct file *file, loff_t offset, int whence)
+{
+	struct affs_dir_data *data = file->private_data;
+
+	return generic_llseek_cookie(file, offset, whence, &data->cookie);
+}
+
+static int affs_dir_open(struct inode *inode, struct file *file)
+{
+	struct affs_dir_data	*data;
+
+	data = kzalloc_obj(struct affs_dir_data);
+	if (!data)
+		return -ENOMEM;
+	file->private_data = data;
+	return 0;
+}
+
+static int affs_dir_release(struct inode *inode, struct file *file)
+{
+	kfree(file->private_data);
+	return 0;
+}
+
+const struct file_operations affs_dir_operations = {
+	.open		= affs_dir_open,
+	.read		= generic_read_dir,
+	.llseek		= affs_dir_llseek,
+	.iterate_shared	= affs_readdir,
+	.fsync		= affs_file_fsync,
+	.release	= affs_dir_release,
+	.setlease	= generic_setlease,
+};
+
+/*
+ * directories can handle most operations...
+ */
+const struct inode_operations affs_dir_inode_operations = {
+	.create		= affs_create,
+	.lookup		= affs_lookup,
+	.link		= affs_link,
+	.unlink		= affs_unlink,
+	.symlink	= affs_symlink,
+	.mkdir		= affs_mkdir,
+	.rmdir		= affs_rmdir,
+	.rename		= affs_rename2,
+	.setattr	= affs_setattr,
+};
+
+static int
+affs_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct inode		*inode = file_inode(file);
+	struct affs_dir_data	*data = file->private_data;
+	struct super_block	*sb = inode->i_sb;
+	struct buffer_head	*dir_bh = NULL;
+	struct buffer_head	*fh_bh = NULL;
+	unsigned char		*name;
+	int			 namelen;
+	u32			 i;
+	int			 hash_pos;
+	int			 chain_pos;
+	u32			 ino;
+	int			 error = 0;
+
+	pr_debug("%s(ino=%llu,f_pos=%llx)\n", __func__, inode->i_ino, ctx->pos);
+
+	if (ctx->pos < 2) {
+		data->ino = 0;
+		if (!dir_emit_dots(file, ctx))
+			return 0;
+	}
+
+	affs_lock_dir(inode);
+	chain_pos = (ctx->pos - 2) & 0xffff;
+	hash_pos  = (ctx->pos - 2) >> 16;
+	if (chain_pos == 0xffff) {
+		affs_warning(sb, "readdir", "More than 65535 entries in chain");
+		chain_pos = 0;
+		hash_pos++;
+		ctx->pos = ((hash_pos << 16) | chain_pos) + 2;
+	}
+	dir_bh = affs_bread(sb, inode->i_ino);
+	if (!dir_bh)
+		goto out_unlock_dir;
+
+	/* If the directory hasn't changed since the last call to readdir(),
+	 * we can jump directly to where we left off.
+	 */
+	ino = data->ino;
+	if (ino && inode_eq_iversion(inode, data->cookie)) {
+		pr_debug("readdir() left off=%d\n", ino);
+		goto inside;
+	}
+	if (hash_pos >= AFFS_SB(sb)->s_hashsize)
+		goto done;
+
+	ino = be32_to_cpu(AFFS_HEAD(dir_bh)->table[hash_pos]);
+	for (i = 0; ino && i < chain_pos; i++) {
+		fh_bh = affs_bread(sb, ino);
+		if (!fh_bh) {
+			affs_error(sb, "readdir","Cannot read block %d", i);
+			error = -EIO;
+			goto out_brelse_dir;
+		}
+		ino = be32_to_cpu(AFFS_TAIL(sb, fh_bh)->hash_chain);
+		affs_brelse(fh_bh);
+		fh_bh = NULL;
+	}
+	if (ino)
+		goto inside;
+	hash_pos++;
+
+	for (; hash_pos < AFFS_SB(sb)->s_hashsize; hash_pos++) {
+		ino = be32_to_cpu(AFFS_HEAD(dir_bh)->table[hash_pos]);
+		if (!ino)
+			continue;
+		ctx->pos = (hash_pos << 16) + 2;
+inside:
+		do {
+			fh_bh = affs_bread(sb, ino);
+			if (!fh_bh) {
+				affs_error(sb, "readdir",
+					   "Cannot read block %d", ino);
+				break;
+			}
+
+			namelen = min(AFFS_TAIL(sb, fh_bh)->name[0],
+				      (u8)AFFSNAMEMAX);
+			name = AFFS_TAIL(sb, fh_bh)->name + 1;
+			pr_debug("readdir(): dir_emit(\"%.*s\", ino=%u), hash=%d, f_pos=%llx\n",
+				 namelen, name, ino, hash_pos, ctx->pos);
+
+			if (!dir_emit(ctx, name, namelen, ino, DT_UNKNOWN))
+				goto done;
+			ctx->pos++;
+			ino = be32_to_cpu(AFFS_TAIL(sb, fh_bh)->hash_chain);
+			affs_brelse(fh_bh);
+			fh_bh = NULL;
+		} while (ino);
+	}
+done:
+	data->cookie = inode_query_iversion(inode);
+	data->ino = ino;
+	affs_brelse(fh_bh);
+
+out_brelse_dir:
+	affs_brelse(dir_bh);
+
+out_unlock_dir:
+	affs_unlock_dir(inode);
+	return error;
+}