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, 47 insertions, 0 deletions

diff --git a/include/crypto/pkcs7.h b/include/crypto/pkcs7.h
new file mode 100644
index 000000000..38ec7f5f9
--- /dev/null
+++ b/include/crypto/pkcs7.h
@@ -0,0 +1,47 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* PKCS#7 crypto data parser
+ *
+ * Copyright (C) 2012 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _CRYPTO_PKCS7_H
+#define _CRYPTO_PKCS7_H
+
+#include <linux/verification.h>
+#include <linux/hash_info.h>
+#include <crypto/public_key.h>
+
+struct key;
+struct pkcs7_message;
+
+/*
+ * pkcs7_parser.c
+ */
+extern struct pkcs7_message *pkcs7_parse_message(const void *data,
+						 size_t datalen);
+extern void pkcs7_free_message(struct pkcs7_message *pkcs7);
+
+extern int pkcs7_get_content_data(const struct pkcs7_message *pkcs7,
+				  const void **_data, size_t *_datalen,
+				  size_t *_headerlen);
+
+/*
+ * pkcs7_trust.c
+ */
+extern int pkcs7_validate_trust(struct pkcs7_message *pkcs7,
+				struct key *trust_keyring);
+
+/*
+ * pkcs7_verify.c
+ */
+extern int pkcs7_verify(struct pkcs7_message *pkcs7,
+			enum key_being_used_for usage);
+
+extern int pkcs7_supply_detached_data(struct pkcs7_message *pkcs7,
+				      const void *data, size_t datalen);
+
+extern int pkcs7_get_digest(struct pkcs7_message *pkcs7, const u8 **buf,
+			    u32 *len, enum hash_algo *hash_algo);
+
+#endif /* _CRYPTO_PKCS7_H */