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, 81 insertions, 0 deletions

diff --git a/lib/crypto/mips/sha1.h b/lib/crypto/mips/sha1.h
new file mode 100644
index 000000000..ba1965002
--- /dev/null
+++ b/lib/crypto/mips/sha1.h
@@ -0,0 +1,81 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Cryptographic API.
+ *
+ * SHA1 Secure Hash Algorithm.
+ *
+ * Adapted for OCTEON by Aaro Koskinen <aaro.koskinen@iki.fi>.
+ *
+ * Based on crypto/sha1_generic.c, which is:
+ *
+ * Copyright (c) Alan Smithee.
+ * Copyright (c) Andrew McDonald <andrew@mcdonald.org.uk>
+ * Copyright (c) Jean-Francois Dive <jef@linuxbe.org>
+ */
+
+#include <asm/octeon/crypto.h>
+#include <asm/octeon/octeon.h>
+
+/*
+ * We pass everything as 64-bit. OCTEON can handle misaligned data.
+ */
+
+static void octeon_sha1_store_hash(struct sha1_block_state *state)
+{
+	u64 *hash = (u64 *)&state->h[0];
+	union {
+		u32 word[2];
+		u64 dword;
+	} hash_tail = { { state->h[4], } };
+
+	write_octeon_64bit_hash_dword(hash[0], 0);
+	write_octeon_64bit_hash_dword(hash[1], 1);
+	write_octeon_64bit_hash_dword(hash_tail.dword, 2);
+	memzero_explicit(&hash_tail.word[0], sizeof(hash_tail.word[0]));
+}
+
+static void octeon_sha1_read_hash(struct sha1_block_state *state)
+{
+	u64 *hash = (u64 *)&state->h[0];
+	union {
+		u32 word[2];
+		u64 dword;
+	} hash_tail;
+
+	hash[0]		= read_octeon_64bit_hash_dword(0);
+	hash[1]		= read_octeon_64bit_hash_dword(1);
+	hash_tail.dword	= read_octeon_64bit_hash_dword(2);
+	state->h[4]	= hash_tail.word[0];
+	memzero_explicit(&hash_tail.dword, sizeof(hash_tail.dword));
+}
+
+static void sha1_blocks(struct sha1_block_state *state,
+			const u8 *data, size_t nblocks)
+{
+	struct octeon_cop2_state cop2_state;
+	unsigned long flags;
+
+	if (!octeon_has_crypto())
+		return sha1_blocks_generic(state, data, nblocks);
+
+	flags = octeon_crypto_enable(&cop2_state);
+	octeon_sha1_store_hash(state);
+
+	do {
+		const u64 *block = (const u64 *)data;
+
+		write_octeon_64bit_block_dword(block[0], 0);
+		write_octeon_64bit_block_dword(block[1], 1);
+		write_octeon_64bit_block_dword(block[2], 2);
+		write_octeon_64bit_block_dword(block[3], 3);
+		write_octeon_64bit_block_dword(block[4], 4);
+		write_octeon_64bit_block_dword(block[5], 5);
+		write_octeon_64bit_block_dword(block[6], 6);
+		octeon_sha1_start(block[7]);
+
+		data += SHA1_BLOCK_SIZE;
+	} while (--nblocks);
+
+	octeon_sha1_read_hash(state);
+	octeon_crypto_disable(&cop2_state, flags);
+}