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, 162 insertions, 0 deletions

diff --git a/fs/udf/dir.c b/fs/udf/dir.c
new file mode 100644
index 000000000..425e3c162
--- /dev/null
+++ b/fs/udf/dir.c
@@ -0,0 +1,162 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * dir.c
+ *
+ * PURPOSE
+ *  Directory handling routines for the OSTA-UDF(tm) filesystem.
+ *
+ * COPYRIGHT
+ *  (C) 1998-2004 Ben Fennema
+ *
+ * HISTORY
+ *
+ *  10/05/98 dgb  Split directory operations into its own file
+ *                Implemented directory reads via do_udf_readdir
+ *  10/06/98      Made directory operations work!
+ *  11/17/98      Rewrote directory to support ICBTAG_FLAG_AD_LONG
+ *  11/25/98 blf  Rewrote directory handling (readdir+lookup) to support reading
+ *                across blocks.
+ *  12/12/98      Split out the lookup code to namei.c. bulk of directory
+ *                code now in directory.c:udf_fileident_read.
+ */
+
+#include "udfdecl.h"
+
+#include <linux/string.h>
+#include <linux/errno.h>
+#include <linux/filelock.h>
+#include <linux/mm.h>
+#include <linux/slab.h>
+#include <linux/bio.h>
+#include <linux/iversion.h>
+
+#include "udf_i.h"
+#include "udf_sb.h"
+
+static int udf_readdir(struct file *file, struct dir_context *ctx)
+{
+	struct inode *dir = file_inode(file);
+	loff_t nf_pos, emit_pos = 0;
+	int flen;
+	unsigned char *fname = NULL;
+	int ret = 0;
+	struct super_block *sb = dir->i_sb;
+	bool pos_valid = false;
+	struct udf_fileident_iter iter;
+
+	if (ctx->pos == 0) {
+		if (!dir_emit_dot(file, ctx))
+			return 0;
+		ctx->pos = 1;
+	}
+	nf_pos = (ctx->pos - 1) << 2;
+	if (nf_pos >= dir->i_size)
+		goto out;
+
+	/*
+	 * Something changed since last readdir (either lseek was called or dir
+	 * changed)?  We need to verify the position correctly points at the
+	 * beginning of some dir entry so that the directory parsing code does
+	 * not get confused. Since UDF does not have any reliable way of
+	 * identifying beginning of dir entry (names are under user control),
+	 * we need to scan the directory from the beginning.
+	 */
+	if (!inode_eq_iversion(dir, *(u64 *)file->private_data)) {
+		emit_pos = nf_pos;
+		nf_pos = 0;
+	} else {
+		pos_valid = true;
+	}
+
+	fname = kmalloc(UDF_NAME_LEN, GFP_KERNEL);
+	if (!fname) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	for (ret = udf_fiiter_init(&iter, dir, nf_pos);
+	     !ret && iter.pos < dir->i_size;
+	     ret = udf_fiiter_advance(&iter)) {
+		struct kernel_lb_addr tloc;
+		udf_pblk_t iblock;
+
+		/* Still not at offset where user asked us to read from? */
+		if (iter.pos < emit_pos)
+			continue;
+
+		/* Update file position only if we got past the current one */
+		pos_valid = true;
+		ctx->pos = (iter.pos >> 2) + 1;
+
+		if (iter.fi.fileCharacteristics & FID_FILE_CHAR_DELETED) {
+			if (!UDF_QUERY_FLAG(sb, UDF_FLAG_UNDELETE))
+				continue;
+		}
+
+		if (iter.fi.fileCharacteristics & FID_FILE_CHAR_HIDDEN) {
+			if (!UDF_QUERY_FLAG(sb, UDF_FLAG_UNHIDE))
+				continue;
+		}
+
+		if (iter.fi.fileCharacteristics & FID_FILE_CHAR_PARENT) {
+			if (!dir_emit_dotdot(file, ctx))
+				goto out_iter;
+			continue;
+		}
+
+		flen = udf_get_filename(sb, iter.name,
+				iter.fi.lengthFileIdent, fname, UDF_NAME_LEN);
+		if (flen < 0)
+			continue;
+
+		tloc = lelb_to_cpu(iter.fi.icb.extLocation);
+		iblock = udf_get_lb_pblock(sb, &tloc, 0);
+		if (!dir_emit(ctx, fname, flen, iblock, DT_UNKNOWN))
+			goto out_iter;
+	}
+
+	if (!ret) {
+		ctx->pos = (iter.pos >> 2) + 1;
+		pos_valid = true;
+	}
+out_iter:
+	udf_fiiter_release(&iter);
+out:
+	if (pos_valid)
+		*(u64 *)file->private_data = inode_query_iversion(dir);
+	kfree(fname);
+
+	return ret;
+}
+
+static int udf_dir_open(struct inode *inode, struct file *file)
+{
+	file->private_data = kzalloc(sizeof(u64), GFP_KERNEL);
+	if (!file->private_data)
+		return -ENOMEM;
+	return 0;
+}
+
+static int udf_dir_release(struct inode *inode, struct file *file)
+{
+	kfree(file->private_data);
+	return 0;
+}
+
+static loff_t udf_dir_llseek(struct file *file, loff_t offset, int whence)
+{
+	return generic_llseek_cookie(file, offset, whence,
+				     (u64 *)file->private_data);
+}
+
+/* readdir and lookup functions */
+const struct file_operations udf_dir_operations = {
+	.open			= udf_dir_open,
+	.release		= udf_dir_release,
+	.llseek			= udf_dir_llseek,
+	.read			= generic_read_dir,
+	.iterate_shared		= udf_readdir,
+	.unlocked_ioctl		= udf_ioctl,
+	.fsync			= simple_fsync,
+	.setlease		= generic_setlease,
+};