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, 109 insertions, 0 deletions

diff --git a/include/crypto/internal/scompress.h b/include/crypto/internal/scompress.h
new file mode 100644
index 000000000..13a0851a9
--- /dev/null
+++ b/include/crypto/internal/scompress.h
@@ -0,0 +1,109 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Synchronous Compression operations
+ *
+ * Copyright 2015 LG Electronics Inc.
+ * Copyright (c) 2016, Intel Corporation
+ * Author: Giovanni Cabiddu <giovanni.cabiddu@intel.com>
+ */
+#ifndef _CRYPTO_SCOMP_INT_H
+#define _CRYPTO_SCOMP_INT_H
+
+#include <crypto/internal/acompress.h>
+
+struct crypto_scomp {
+	struct crypto_tfm base;
+};
+
+/**
+ * struct scomp_alg - synchronous compression algorithm
+ *
+ * @compress:	Function performs a compress operation
+ * @decompress:	Function performs a de-compress operation
+ * @streams:	Per-cpu memory for algorithm
+ * @calg:	Cmonn algorithm data structure shared with acomp
+ * @COMP_ALG_COMMON: see struct comp_alg_common
+ */
+struct scomp_alg {
+	int (*compress)(struct crypto_scomp *tfm, const u8 *src,
+			unsigned int slen, u8 *dst, unsigned int *dlen,
+			void *ctx);
+	int (*decompress)(struct crypto_scomp *tfm, const u8 *src,
+			  unsigned int slen, u8 *dst, unsigned int *dlen,
+			  void *ctx);
+
+	struct crypto_acomp_streams streams;
+
+	union {
+		struct COMP_ALG_COMMON;
+		struct comp_alg_common calg;
+	};
+};
+
+static inline struct scomp_alg *__crypto_scomp_alg(struct crypto_alg *alg)
+{
+	return container_of(alg, struct scomp_alg, base);
+}
+
+static inline struct crypto_scomp *__crypto_scomp_tfm(struct crypto_tfm *tfm)
+{
+	return container_of(tfm, struct crypto_scomp, base);
+}
+
+static inline struct crypto_tfm *crypto_scomp_tfm(struct crypto_scomp *tfm)
+{
+	return &tfm->base;
+}
+
+static inline void crypto_free_scomp(struct crypto_scomp *tfm)
+{
+	crypto_destroy_tfm(tfm, crypto_scomp_tfm(tfm));
+}
+
+static inline struct scomp_alg *crypto_scomp_alg(struct crypto_scomp *tfm)
+{
+	return __crypto_scomp_alg(crypto_scomp_tfm(tfm)->__crt_alg);
+}
+
+static inline int crypto_scomp_compress(struct crypto_scomp *tfm,
+					const u8 *src, unsigned int slen,
+					u8 *dst, unsigned int *dlen, void *ctx)
+{
+	return crypto_scomp_alg(tfm)->compress(tfm, src, slen, dst, dlen, ctx);
+}
+
+static inline int crypto_scomp_decompress(struct crypto_scomp *tfm,
+					  const u8 *src, unsigned int slen,
+					  u8 *dst, unsigned int *dlen,
+					  void *ctx)
+{
+	return crypto_scomp_alg(tfm)->decompress(tfm, src, slen, dst, dlen,
+						 ctx);
+}
+
+/**
+ * crypto_register_scomp() -- Register synchronous compression algorithm
+ *
+ * Function registers an implementation of a synchronous
+ * compression algorithm
+ *
+ * @alg:	algorithm definition
+ *
+ * Return: zero on success; error code in case of error
+ */
+int crypto_register_scomp(struct scomp_alg *alg);
+
+/**
+ * crypto_unregister_scomp() -- Unregister synchronous compression algorithm
+ *
+ * Function unregisters an implementation of a synchronous
+ * compression algorithm
+ *
+ * @alg:	algorithm definition
+ */
+void crypto_unregister_scomp(struct scomp_alg *alg);
+
+int crypto_register_scomps(struct scomp_alg *algs, int count);
+void crypto_unregister_scomps(struct scomp_alg *algs, int count);
+
+#endif