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, 52 insertions, 0 deletions

diff --git a/lib/crypto/arm64/sha3.h b/lib/crypto/arm64/sha3.h
new file mode 100644
index 000000000..eaaba3224
--- /dev/null
+++ b/lib/crypto/arm64/sha3.h
@@ -0,0 +1,52 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2018 Linaro Ltd <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <asm/simd.h>
+#include <linux/cpufeature.h>
+
+static __ro_after_init DEFINE_STATIC_KEY_FALSE(have_sha3);
+
+asmlinkage void sha3_ce_transform(struct sha3_state *state, const u8 *data,
+				  size_t nblocks, size_t block_size);
+
+static void sha3_absorb_blocks(struct sha3_state *state, const u8 *data,
+			       size_t nblocks, size_t block_size)
+{
+	if (static_branch_likely(&have_sha3) && likely(may_use_simd())) {
+		scoped_ksimd()
+			sha3_ce_transform(state, data, nblocks, block_size);
+	} else {
+		sha3_absorb_blocks_generic(state, data, nblocks, block_size);
+	}
+}
+
+static void sha3_keccakf(struct sha3_state *state)
+{
+	if (static_branch_likely(&have_sha3) && likely(may_use_simd())) {
+		/*
+		 * Passing zeroes into sha3_ce_transform() gives the plain
+		 * Keccak-f permutation, which is what we want here.  Any
+		 * supported block size may be used.  Use SHA3_512_BLOCK_SIZE
+		 * since it's the shortest.
+		 */
+		static const u8 zeroes[SHA3_512_BLOCK_SIZE];
+
+		scoped_ksimd()
+			sha3_ce_transform(state, zeroes, 1, sizeof(zeroes));
+	} else {
+		sha3_keccakf_generic(state);
+	}
+}
+
+#define sha3_mod_init_arch sha3_mod_init_arch
+static void sha3_mod_init_arch(void)
+{
+	if (cpu_have_named_feature(SHA3))
+		static_branch_enable(&have_sha3);
+}