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, 150 insertions, 0 deletions

diff --git a/fs/hfs/trans.c b/fs/hfs/trans.c
new file mode 100644
index 000000000..fdb0edb8a
--- /dev/null
+++ b/fs/hfs/trans.c
@@ -0,0 +1,150 @@
+/*
+ *  linux/fs/hfs/trans.c
+ *
+ * Copyright (C) 1995-1997  Paul H. Hargrove
+ * This file may be distributed under the terms of the GNU General Public License.
+ *
+ * This file contains routines for converting between the Macintosh
+ * character set and various other encodings.  This includes dealing
+ * with ':' vs. '/' as the path-element separator.
+ */
+
+#include <linux/types.h>
+#include <linux/nls.h>
+
+#include "hfs_fs.h"
+
+/*================ Global functions ================*/
+
+/*
+ * hfs_mac2asc()
+ *
+ * Given a 'Pascal String' (a string preceded by a length byte) in
+ * the Macintosh character set produce the corresponding filename using
+ * the 'trivial' name-mangling scheme, returning the length of the
+ * mangled filename.  Note that the output string is not NULL
+ * terminated.
+ *
+ * The name-mangling works as follows:
+ * The character '/', which is illegal in Linux filenames is replaced
+ * by ':' which never appears in HFS filenames.	 All other characters
+ * are passed unchanged from input to output.
+ */
+int hfs_mac2asc(struct super_block *sb, char *out, const struct hfs_name *in)
+{
+	struct nls_table *nls_disk = HFS_SB(sb)->nls_disk;
+	struct nls_table *nls_io = HFS_SB(sb)->nls_io;
+	const char *src;
+	char *dst;
+	int srclen, dstlen, size;
+
+	src = in->name;
+	srclen = in->len;
+	if (srclen > HFS_NAMELEN)
+		srclen = HFS_NAMELEN;
+	dst = out;
+	dstlen = HFS_MAX_NAMELEN;
+	if (nls_io) {
+		wchar_t ch;
+
+		while (srclen > 0) {
+			if (nls_disk) {
+				size = nls_disk->char2uni(src, srclen, &ch);
+				if (size <= 0) {
+					ch = '?';
+					size = 1;
+				}
+				src += size;
+				srclen -= size;
+			} else {
+				ch = *src++;
+				srclen--;
+			}
+			if (ch == '/')
+				ch = ':';
+			size = nls_io->uni2char(ch, dst, dstlen);
+			if (size < 0) {
+				if (size == -ENAMETOOLONG)
+					goto out;
+				*dst = '?';
+				size = 1;
+			}
+			dst += size;
+			dstlen -= size;
+		}
+	} else {
+		char ch;
+
+		while (--srclen >= 0)
+			*dst++ = (ch = *src++) == '/' ? ':' : ch;
+	}
+out:
+	return dst - out;
+}
+
+/*
+ * hfs_asc2mac()
+ *
+ * Given an ASCII string (not null-terminated) and its length,
+ * generate the corresponding filename in the Macintosh character set
+ * using the 'trivial' name-mangling scheme, returning the length of
+ * the mangled filename.  Note that the output string is not NULL
+ * terminated.
+ *
+ * This routine is a inverse to hfs_mac2triv().
+ * A ':' is replaced by a '/'.
+ */
+void hfs_asc2mac(struct super_block *sb, struct hfs_name *out, const struct qstr *in)
+{
+	struct nls_table *nls_disk = HFS_SB(sb)->nls_disk;
+	struct nls_table *nls_io = HFS_SB(sb)->nls_io;
+	const char *src;
+	char *dst;
+	int srclen, dstlen, size;
+
+	src = in->name;
+	srclen = in->len;
+	dst = out->name;
+	dstlen = HFS_NAMELEN;
+	if (nls_io) {
+		wchar_t ch;
+
+		while (srclen > 0 && dstlen > 0) {
+			size = nls_io->char2uni(src, srclen, &ch);
+			if (size < 0) {
+				ch = '?';
+				size = 1;
+			}
+			src += size;
+			srclen -= size;
+			if (ch == ':')
+				ch = '/';
+			if (nls_disk) {
+				size = nls_disk->uni2char(ch, dst, dstlen);
+				if (size < 0) {
+					if (size == -ENAMETOOLONG)
+						goto out;
+					*dst = '?';
+					size = 1;
+				}
+				dst += size;
+				dstlen -= size;
+			} else {
+				*dst++ = ch > 0xff ? '?' : ch;
+				dstlen--;
+			}
+		}
+	} else {
+		char ch;
+
+		if (dstlen > srclen)
+			dstlen = srclen;
+		while (--dstlen >= 0)
+			*dst++ = (ch = *src++) == ':' ? '/' : ch;
+	}
+out:
+	out->len = dst - (char *)out->name;
+	dstlen = HFS_NAMELEN - out->len;
+	while (--dstlen >= 0)
+		*dst++ = 0;
+}