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, 99 insertions, 0 deletions

diff --git a/crypto/tcrypt.h b/crypto/tcrypt.h
new file mode 100644
index 000000000..85c3f77bc
--- /dev/null
+++ b/crypto/tcrypt.h
@@ -0,0 +1,99 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Quick & dirty crypto benchmarking module.
+ *
+ * This will only exist until we have a better benchmarking mechanism
+ * (e.g. a char device).
+ *
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ * Copyright (c) 2002 Jean-Francois Dive <jef@linuxbe.org>
+ * Copyright (c) 2007 Nokia Siemens Networks
+ */
+#ifndef _CRYPTO_TCRYPT_H
+#define _CRYPTO_TCRYPT_H
+
+struct cipher_speed_template {
+	const char *key;
+	unsigned int klen;
+};
+
+struct aead_speed_template {
+	const char *key;
+	unsigned int klen;
+};
+
+struct hash_speed {
+	unsigned int blen;	/* buffer length */
+	unsigned int plen;	/* per-update length */
+};
+
+/*
+ * DES test vectors.
+ */
+#define DES3_SPEED_VECTORS	1
+
+static struct cipher_speed_template des3_speed_template[] = {
+	{
+		.key	= "\x01\x23\x45\x67\x89\xab\xcd\xef"
+			  "\x55\x55\x55\x55\x55\x55\x55\x55"
+			  "\xfe\xdc\xba\x98\x76\x54\x32\x10",
+		.klen	= 24,
+	}
+};
+
+/*
+ * Cipher speed tests
+ */
+static u8 speed_template_8[] = {8, 0};
+static u8 speed_template_16[] = {16, 0};
+static u8 speed_template_24[] = {24, 0};
+static u8 speed_template_8_16[] = {8, 16, 0};
+static u8 speed_template_8_32[] = {8, 32, 0};
+static u8 speed_template_16_32[] = {16, 32, 0};
+static u8 speed_template_16_24_32[] = {16, 24, 32, 0};
+static u8 speed_template_20_28_36[] = {20, 28, 36, 0};
+static u8 speed_template_32_40_48[] = {32, 40, 48, 0};
+static u8 speed_template_32_48[] = {32, 48, 0};
+static u8 speed_template_32_48_64[] = {32, 48, 64, 0};
+static u8 speed_template_32_64[] = {32, 64, 0};
+static u8 speed_template_32[] = {32, 0};
+
+/*
+ * AEAD speed tests
+ */
+static u8 aead_speed_template_19[] = {19, 0};
+static u8 aead_speed_template_20_28_36[] = {20, 28, 36, 0};
+static u8 aead_speed_template_36[] = {36, 0};
+
+/*
+ * Digest speed tests
+ */
+static struct hash_speed generic_hash_speed_template[] = {
+	{ .blen = 16,	.plen = 16, },
+	{ .blen = 64,	.plen = 16, },
+	{ .blen = 64,	.plen = 64, },
+	{ .blen = 256,	.plen = 16, },
+	{ .blen = 256,	.plen = 64, },
+	{ .blen = 256,	.plen = 256, },
+	{ .blen = 1024,	.plen = 16, },
+	{ .blen = 1024,	.plen = 256, },
+	{ .blen = 1024,	.plen = 1024, },
+	{ .blen = 2048,	.plen = 16, },
+	{ .blen = 2048,	.plen = 256, },
+	{ .blen = 2048,	.plen = 1024, },
+	{ .blen = 2048,	.plen = 2048, },
+	{ .blen = 4096,	.plen = 16, },
+	{ .blen = 4096,	.plen = 256, },
+	{ .blen = 4096,	.plen = 1024, },
+	{ .blen = 4096,	.plen = 4096, },
+	{ .blen = 8192,	.plen = 16, },
+	{ .blen = 8192,	.plen = 256, },
+	{ .blen = 8192,	.plen = 1024, },
+	{ .blen = 8192,	.plen = 4096, },
+	{ .blen = 8192,	.plen = 8192, },
+
+	/* End marker */
+	{  .blen = 0,	.plen = 0, }
+};
+
+#endif	/* _CRYPTO_TCRYPT_H */