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, 35 insertions, 0 deletions

diff --git a/include/keys/asymmetric-parser.h b/include/keys/asymmetric-parser.h
new file mode 100644
index 000000000..516a3f511
--- /dev/null
+++ b/include/keys/asymmetric-parser.h
@@ -0,0 +1,35 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Asymmetric public-key cryptography data parser
+ *
+ * See Documentation/crypto/asymmetric-keys.rst
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _KEYS_ASYMMETRIC_PARSER_H
+#define _KEYS_ASYMMETRIC_PARSER_H
+
+struct key_preparsed_payload;
+
+/*
+ * Key data parser.  Called during key instantiation.
+ */
+struct asymmetric_key_parser {
+	struct list_head	link;
+	struct module		*owner;
+	const char		*name;
+
+	/* Attempt to parse a key from the data blob passed to add_key() or
+	 * keyctl_instantiate().  Should also generate a proposed description
+	 * that the caller can optionally use for the key.
+	 *
+	 * Return EBADMSG if not recognised.
+	 */
+	int (*parse)(struct key_preparsed_payload *prep);
+};
+
+extern int register_asymmetric_key_parser(struct asymmetric_key_parser *);
+extern void unregister_asymmetric_key_parser(struct asymmetric_key_parser *);
+
+#endif /* _KEYS_ASYMMETRIC_PARSER_H */