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, 125 insertions, 0 deletions

diff --git a/fs/jfs/jfs_unicode.c b/fs/jfs/jfs_unicode.c
new file mode 100644
index 000000000..0c1e90272
--- /dev/null
+++ b/fs/jfs/jfs_unicode.c
@@ -0,0 +1,125 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *   Copyright (C) International Business Machines Corp., 2000-2004
+ */
+
+#include <linux/fs.h>
+#include <linux/slab.h>
+#include "jfs_incore.h"
+#include "jfs_filsys.h"
+#include "jfs_unicode.h"
+#include "jfs_debug.h"
+
+/*
+ * NAME:	jfs_strfromUCS()
+ *
+ * FUNCTION:	Convert little-endian unicode string to character string
+ *
+ */
+int jfs_strfromUCS_le(char *to, const __le16 * from,
+		      int len, struct nls_table *codepage)
+{
+	int i;
+	int outlen = 0;
+	static int warn_again = 5;	/* Only warn up to 5 times total */
+	int warn = !!warn_again;	/* once per string */
+
+	if (codepage) {
+		for (i = 0; (i < len) && from[i]; i++) {
+			int charlen;
+			charlen =
+			    codepage->uni2char(le16_to_cpu(from[i]),
+					       &to[outlen],
+					       NLS_MAX_CHARSET_SIZE);
+			if (charlen > 0)
+				outlen += charlen;
+			else
+				to[outlen++] = '?';
+		}
+	} else {
+		for (i = 0; (i < len) && from[i]; i++) {
+			if (unlikely(le16_to_cpu(from[i]) & 0xff00)) {
+				to[i] = '?';
+				if (unlikely(warn)) {
+					warn--;
+					warn_again--;
+					printk(KERN_ERR
+			"non-latin1 character 0x%x found in JFS file name\n",
+					       le16_to_cpu(from[i]));
+					printk(KERN_ERR
+				"mount with iocharset=utf8 to access\n");
+				}
+
+			}
+			else
+				to[i] = (char) (le16_to_cpu(from[i]));
+		}
+		outlen = i;
+	}
+	to[outlen] = 0;
+	return outlen;
+}
+
+/*
+ * NAME:	jfs_strtoUCS()
+ *
+ * FUNCTION:	Convert character string to unicode string
+ *
+ */
+static int jfs_strtoUCS(wchar_t * to, const unsigned char *from, int len,
+		struct nls_table *codepage)
+{
+	int charlen;
+	int i;
+
+	if (codepage) {
+		for (i = 0; len && *from; i++, from += charlen, len -= charlen)
+		{
+			charlen = codepage->char2uni(from, len, &to[i]);
+			if (charlen < 1) {
+				jfs_err("jfs_strtoUCS: char2uni returned %d.",
+					charlen);
+				jfs_err("charset = %s, char = 0x%x",
+					codepage->charset, *from);
+				return charlen;
+			}
+		}
+	} else {
+		for (i = 0; (i < len) && from[i]; i++)
+			to[i] = (wchar_t) from[i];
+	}
+
+	to[i] = 0;
+	return i;
+}
+
+/*
+ * NAME:	get_UCSname()
+ *
+ * FUNCTION:	Allocate and translate to unicode string
+ *
+ */
+int get_UCSname(struct component_name * uniName, struct dentry *dentry)
+{
+	struct nls_table *nls_tab = JFS_SBI(dentry->d_sb)->nls_tab;
+	int length = dentry->d_name.len;
+
+	if (length > JFS_NAME_MAX)
+		return -ENAMETOOLONG;
+
+	uniName->name =
+	    kmalloc_array(length + 1, sizeof(wchar_t), GFP_NOFS);
+
+	if (uniName->name == NULL)
+		return -ENOMEM;
+
+	uniName->namlen = jfs_strtoUCS(uniName->name, dentry->d_name.name,
+				       length, nls_tab);
+
+	if (uniName->namlen < 0) {
+		kfree(uniName->name);
+		return uniName->namlen;
+	}
+
+	return 0;
+}