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, 79 insertions, 0 deletions

diff --git a/crypto/aegis.h b/crypto/aegis.h
new file mode 100644
index 000000000..ffcf8e85e
--- /dev/null
+++ b/crypto/aegis.h
@@ -0,0 +1,79 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * AEGIS common definitions
+ *
+ * Copyright (c) 2018 Ondrej Mosnacek <omosnacek@gmail.com>
+ * Copyright (c) 2018 Red Hat, Inc. All rights reserved.
+ */
+
+#ifndef _CRYPTO_AEGIS_H
+#define _CRYPTO_AEGIS_H
+
+#include <crypto/aes.h>
+#include <linux/bitops.h>
+#include <linux/types.h>
+
+#define AEGIS_BLOCK_SIZE 16
+
+union aegis_block {
+	__le64 words64[AEGIS_BLOCK_SIZE / sizeof(__le64)];
+	__le32 words32[AEGIS_BLOCK_SIZE / sizeof(__le32)];
+	u8 bytes[AEGIS_BLOCK_SIZE];
+};
+
+struct aegis_state;
+
+extern int aegis128_have_aes_insn;
+
+#define AEGIS_BLOCK_ALIGN (__alignof__(union aegis_block))
+#define AEGIS_ALIGNED(p) IS_ALIGNED((uintptr_t)p, AEGIS_BLOCK_ALIGN)
+
+bool crypto_aegis128_have_simd(void);
+void crypto_aegis128_update_simd(struct aegis_state *state, const void *msg);
+void crypto_aegis128_init_simd(struct aegis_state *state,
+			       const union aegis_block *key,
+			       const u8 *iv);
+void crypto_aegis128_encrypt_chunk_simd(struct aegis_state *state, u8 *dst,
+					const u8 *src, unsigned int size);
+void crypto_aegis128_decrypt_chunk_simd(struct aegis_state *state, u8 *dst,
+					const u8 *src, unsigned int size);
+int crypto_aegis128_final_simd(struct aegis_state *state,
+			       union aegis_block *tag_xor,
+			       unsigned int assoclen,
+			       unsigned int cryptlen,
+			       unsigned int authsize);
+
+static __always_inline void crypto_aegis_block_xor(union aegis_block *dst,
+						   const union aegis_block *src)
+{
+	dst->words64[0] ^= src->words64[0];
+	dst->words64[1] ^= src->words64[1];
+}
+
+static __always_inline void crypto_aegis_block_and(union aegis_block *dst,
+						   const union aegis_block *src)
+{
+	dst->words64[0] &= src->words64[0];
+	dst->words64[1] &= src->words64[1];
+}
+
+static __always_inline void crypto_aegis_aesenc(union aegis_block *dst,
+						const union aegis_block *src,
+						const union aegis_block *key)
+{
+	const u8  *s  = src->bytes;
+	const u32 *t = aes_enc_tab;
+	u32 d0, d1, d2, d3;
+
+	d0 = t[s[ 0]] ^ rol32(t[s[ 5]], 8) ^ rol32(t[s[10]], 16) ^ rol32(t[s[15]], 24);
+	d1 = t[s[ 4]] ^ rol32(t[s[ 9]], 8) ^ rol32(t[s[14]], 16) ^ rol32(t[s[ 3]], 24);
+	d2 = t[s[ 8]] ^ rol32(t[s[13]], 8) ^ rol32(t[s[ 2]], 16) ^ rol32(t[s[ 7]], 24);
+	d3 = t[s[12]] ^ rol32(t[s[ 1]], 8) ^ rol32(t[s[ 6]], 16) ^ rol32(t[s[11]], 24);
+
+	dst->words32[0] = cpu_to_le32(d0) ^ key->words32[0];
+	dst->words32[1] = cpu_to_le32(d1) ^ key->words32[1];
+	dst->words32[2] = cpu_to_le32(d2) ^ key->words32[2];
+	dst->words32[3] = cpu_to_le32(d3) ^ key->words32[3];
+}
+
+#endif /* _CRYPTO_AEGIS_H */