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, 303 insertions, 0 deletions

diff --git a/fs/isofs/dir.c b/fs/isofs/dir.c
new file mode 100644
index 000000000..cc587cd25
--- /dev/null
+++ b/fs/isofs/dir.c
@@ -0,0 +1,303 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/isofs/dir.c
+ *
+ *  (C) 1992, 1993, 1994  Eric Youngdale Modified for ISO 9660 filesystem.
+ *
+ *  (C) 1991  Linus Torvalds - minix filesystem
+ *
+ *  Steve Beynon		       : Missing last directory entries fixed
+ *  (stephen@askone.demon.co.uk)      : 21st June 1996
+ *
+ *  isofs directory handling functions
+ */
+#include <linux/gfp.h>
+#include <linux/filelock.h>
+#include <linux/slab.h>
+#include "isofs.h"
+#include <linux/fileattr.h>
+
+int isofs_name_translate(struct iso_directory_record *de, char *new, struct inode *inode)
+{
+	char * old = de->name;
+	int len = de->name_len[0];
+	int i;
+
+	for (i = 0; i < len; i++) {
+		unsigned char c = old[i];
+		if (!c)
+			break;
+
+		if (c >= 'A' && c <= 'Z')
+			c |= 0x20;	/* lower case */
+
+		/* Drop trailing '.;1' (ISO 9660:1988 7.5.1 requires period) */
+		if (c == '.' && i == len - 3 && old[i + 1] == ';' && old[i + 2] == '1')
+			break;
+
+		/* Drop trailing ';1' */
+		if (c == ';' && i == len - 2 && old[i + 1] == '1')
+			break;
+
+		/* Convert remaining ';' to '.' */
+		/* Also '/' to '.' (broken Acorn-generated ISO9660 images) */
+		if (c == ';' || c == '/')
+			c = '.';
+
+		new[i] = c;
+	}
+	return i;
+}
+
+/* Acorn extensions written by Matthew Wilcox <willy@infradead.org> 1998 */
+int get_acorn_filename(struct iso_directory_record *de,
+			    char *retname, struct inode *inode)
+{
+	int std;
+	unsigned char *chr;
+	int retnamlen = isofs_name_translate(de, retname, inode);
+
+	if (retnamlen == 0)
+		return 0;
+	std = sizeof(struct iso_directory_record) + de->name_len[0];
+	if (std & 1)
+		std++;
+	if (de->length[0] - std != 32)
+		return retnamlen;
+	chr = ((unsigned char *) de) + std;
+	if (strncmp(chr, "ARCHIMEDES", 10))
+		return retnamlen;
+	if ((*retname == '_') && ((chr[19] & 1) == 1))
+		*retname = '!';
+	if (((de->flags[0] & 2) == 0) && (chr[13] == 0xff)
+		&& ((chr[12] & 0xf0) == 0xf0)) {
+		retname[retnamlen] = ',';
+		sprintf(retname+retnamlen+1, "%3.3x",
+			((chr[12] & 0xf) << 8) | chr[11]);
+		retnamlen += 4;
+	}
+	return retnamlen;
+}
+
+/*
+ * This should _really_ be cleaned up some day..
+ */
+static int do_isofs_readdir(struct inode *inode, struct file *file,
+		struct dir_context *ctx,
+		char *tmpname, struct iso_directory_record *tmpde)
+{
+	unsigned long bufsize = ISOFS_BUFFER_SIZE(inode);
+	unsigned char bufbits = ISOFS_BUFFER_BITS(inode);
+	unsigned long block, offset, block_saved, offset_saved;
+	unsigned long inode_number = 0;	/* Quiet GCC */
+	struct buffer_head *bh = NULL;
+	int len;
+	int map;
+	int first_de = 1;
+	char *p = NULL;		/* Quiet GCC */
+	struct iso_directory_record *de;
+	struct isofs_sb_info *sbi = ISOFS_SB(inode->i_sb);
+
+	offset = ctx->pos & (bufsize - 1);
+	block = ctx->pos >> bufbits;
+
+	while (ctx->pos < inode->i_size) {
+		int de_len;
+
+		if (!bh) {
+			bh = isofs_bread(inode, block);
+			if (!bh)
+				return 0;
+		}
+
+		de = (struct iso_directory_record *) (bh->b_data + offset);
+
+		de_len = *(unsigned char *)de;
+
+		/*
+		 * If the length byte is zero, we should move on to the next
+		 * CDROM sector.  If we are at the end of the directory, we
+		 * kick out of the while loop.
+		 */
+
+		if (de_len == 0) {
+			brelse(bh);
+			bh = NULL;
+			ctx->pos = (ctx->pos + ISOFS_BLOCK_SIZE) & ~(ISOFS_BLOCK_SIZE - 1);
+			block = ctx->pos >> bufbits;
+			offset = 0;
+			continue;
+		}
+
+		block_saved = block;
+		offset_saved = offset;
+		offset += de_len;
+
+		/* Make sure we have a full directory entry */
+		if (offset >= bufsize) {
+			int slop = bufsize - offset + de_len;
+			memcpy(tmpde, de, slop);
+			offset &= bufsize - 1;
+			block++;
+			brelse(bh);
+			bh = NULL;
+			if (offset) {
+				bh = isofs_bread(inode, block);
+				if (!bh)
+					return 0;
+				memcpy((void *) tmpde + slop, bh->b_data, offset);
+			}
+			de = tmpde;
+		}
+		/* Basic sanity check, whether name doesn't exceed dir entry */
+		if (de_len < sizeof(struct iso_directory_record) ||
+		    de_len < de->name_len[0] +
+					sizeof(struct iso_directory_record)) {
+			printk(KERN_NOTICE "iso9660: Corrupted directory entry"
+			       " in block %lu of inode %llu\n", block,
+			       inode->i_ino);
+			brelse(bh);
+			return -EIO;
+		}
+
+		if (first_de) {
+			isofs_normalize_block_and_offset(de,
+							&block_saved,
+							&offset_saved);
+			inode_number = isofs_get_ino(block_saved,
+							offset_saved, bufbits);
+		}
+
+		if (de->flags[-sbi->s_high_sierra] & 0x80) {
+			first_de = 0;
+			ctx->pos += de_len;
+			continue;
+		}
+		first_de = 1;
+
+		/* Handle the case of the '.' directory */
+		if (de->name_len[0] == 1 && de->name[0] == 0) {
+			if (!dir_emit_dot(file, ctx))
+				break;
+			ctx->pos += de_len;
+			continue;
+		}
+
+		len = 0;
+
+		/* Handle the case of the '..' directory */
+		if (de->name_len[0] == 1 && de->name[0] == 1) {
+			if (!dir_emit_dotdot(file, ctx))
+				break;
+			ctx->pos += de_len;
+			continue;
+		}
+
+		/* Handle everything else.  Do name translation if there
+		   is no Rock Ridge NM field. */
+
+		/*
+		 * Do not report hidden files if so instructed, or associated
+		 * files unless instructed to do so
+		 */
+		if ((sbi->s_hide && (de->flags[-sbi->s_high_sierra] & 1)) ||
+		    (!sbi->s_showassoc &&
+				(de->flags[-sbi->s_high_sierra] & 4))) {
+			ctx->pos += de_len;
+			continue;
+		}
+
+		map = 1;
+		if (sbi->s_rock) {
+			len = get_rock_ridge_filename(de, tmpname, inode);
+			if (len != 0) {		/* may be -1 */
+				p = tmpname;
+				map = 0;
+			}
+		}
+		if (map) {
+#ifdef CONFIG_JOLIET
+			if (sbi->s_joliet_level) {
+				len = get_joliet_filename(de, tmpname, inode);
+				p = tmpname;
+			} else
+#endif
+			if (sbi->s_mapping == 'a') {
+				len = get_acorn_filename(de, tmpname, inode);
+				p = tmpname;
+			} else
+			if (sbi->s_mapping == 'n') {
+				len = isofs_name_translate(de, tmpname, inode);
+				p = tmpname;
+			} else {
+				p = de->name;
+				len = de->name_len[0];
+			}
+		}
+		if (len > 0) {
+			if (!dir_emit(ctx, p, len, inode_number, DT_UNKNOWN))
+				break;
+		}
+		ctx->pos += de_len;
+	}
+	if (bh)
+		brelse(bh);
+	return 0;
+}
+
+/*
+ * Handle allocation of temporary space for name translation and
+ * handling split directory entries.. The real work is done by
+ * "do_isofs_readdir()".
+ */
+static int isofs_readdir(struct file *file, struct dir_context *ctx)
+{
+	int result;
+	char *tmpname;
+	struct iso_directory_record *tmpde;
+	struct inode *inode = file_inode(file);
+
+	tmpname = kmalloc(PAGE_SIZE, GFP_KERNEL);
+	if (tmpname == NULL)
+		return -ENOMEM;
+
+	tmpde = (struct iso_directory_record *) (tmpname+1024);
+
+	result = do_isofs_readdir(inode, file, ctx, tmpname, tmpde);
+
+	kfree(tmpname);
+	return result;
+}
+
+int isofs_fileattr_get(struct dentry *dentry, struct file_kattr *fa)
+{
+	struct isofs_sb_info *sbi = ISOFS_SB(dentry->d_sb);
+
+	if (sbi->s_check == 'r') {
+		fa->fsx_xflags |= FS_XFLAG_CASEFOLD;
+		fa->flags |= FS_CASEFOLD_FL;
+	}
+	if (!sbi->s_joliet_level && !sbi->s_rock &&
+	    (sbi->s_mapping == 'n' || sbi->s_mapping == 'a'))
+		fa->fsx_xflags |= FS_XFLAG_CASENONPRESERVING;
+	return 0;
+}
+
+const struct file_operations isofs_dir_operations =
+{
+	.llseek = generic_file_llseek,
+	.read = generic_read_dir,
+	.iterate_shared = isofs_readdir,
+	.setlease = generic_setlease,
+};
+
+/*
+ * directories can handle most operations...
+ */
+const struct inode_operations isofs_dir_inode_operations =
+{
+	.lookup = isofs_lookup,
+	.fileattr_get = isofs_fileattr_get,
+};
+
+