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, 210 insertions, 0 deletions

diff --git a/crypto/internal.h b/crypto/internal.h
new file mode 100644
index 000000000..b0a10986f
--- /dev/null
+++ b/crypto/internal.h
@@ -0,0 +1,210 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ * Cryptographic API.
+ *
+ * Copyright (c) 2002 James Morris <jmorris@intercode.com.au>
+ * Copyright (c) 2005 Herbert Xu <herbert@gondor.apana.org.au>
+ */
+#ifndef _CRYPTO_INTERNAL_H
+#define _CRYPTO_INTERNAL_H
+
+#include <crypto/algapi.h>
+#include <linux/completion.h>
+#include <linux/jump_label.h>
+#include <linux/list.h>
+#include <linux/module.h>
+#include <linux/notifier.h>
+#include <linux/numa.h>
+#include <linux/refcount.h>
+#include <linux/rwsem.h>
+#include <linux/scatterlist.h>
+#include <linux/sched.h>
+#include <linux/types.h>
+
+struct crypto_instance;
+struct crypto_template;
+
+struct crypto_larval {
+	struct crypto_alg alg;
+	struct crypto_alg *adult;
+	struct completion completion;
+	u32 mask;
+	bool test_started;
+};
+
+struct crypto_type {
+	unsigned int (*ctxsize)(struct crypto_alg *alg, u32 type, u32 mask);
+	unsigned int (*extsize)(struct crypto_alg *alg);
+	int (*init_tfm)(struct crypto_tfm *tfm);
+	void (*show)(struct seq_file *m, struct crypto_alg *alg);
+	int (*report)(struct sk_buff *skb, struct crypto_alg *alg);
+	void (*free)(struct crypto_instance *inst);
+	void (*destroy)(struct crypto_alg *alg);
+
+	unsigned int type;
+	unsigned int maskclear;
+	unsigned int maskset;
+	unsigned int tfmsize;
+	unsigned int algsize;
+};
+
+enum {
+	CRYPTOA_UNSPEC,
+	CRYPTOA_ALG,
+	CRYPTOA_TYPE,
+	__CRYPTOA_MAX,
+};
+
+#define CRYPTOA_MAX (__CRYPTOA_MAX - 1)
+
+/* Maximum number of (rtattr) parameters for each template. */
+#define CRYPTO_MAX_ATTRS 32
+
+extern struct rw_semaphore crypto_alg_sem;
+extern struct list_head crypto_alg_list __guarded_by(&crypto_alg_sem);
+extern struct blocking_notifier_head crypto_chain;
+
+int alg_test(const char *driver, const char *alg, u32 type, u32 mask);
+
+#if !IS_BUILTIN(CONFIG_CRYPTO_ALGAPI) || !IS_ENABLED(CONFIG_CRYPTO_SELFTESTS)
+static inline bool crypto_boot_test_finished(void)
+{
+	return true;
+}
+static inline void set_crypto_boot_test_finished(void)
+{
+}
+#else
+DECLARE_STATIC_KEY_FALSE(__crypto_boot_test_finished);
+static inline bool crypto_boot_test_finished(void)
+{
+	return static_branch_likely(&__crypto_boot_test_finished);
+}
+static inline void set_crypto_boot_test_finished(void)
+{
+	static_branch_enable(&__crypto_boot_test_finished);
+}
+#endif /* !IS_BUILTIN(CONFIG_CRYPTO_ALGAPI) ||
+	* !IS_ENABLED(CONFIG_CRYPTO_SELFTESTS)
+	*/
+
+#ifdef CONFIG_PROC_FS
+void __init crypto_init_proc(void);
+void __exit crypto_exit_proc(void);
+#else
+static inline void crypto_init_proc(void)
+{ }
+static inline void crypto_exit_proc(void)
+{ }
+#endif
+
+static inline unsigned int crypto_cipher_ctxsize(struct crypto_alg *alg)
+{
+	return alg->cra_ctxsize;
+}
+
+static inline unsigned int crypto_compress_ctxsize(struct crypto_alg *alg)
+{
+	return alg->cra_ctxsize;
+}
+
+struct crypto_alg *crypto_mod_get(struct crypto_alg *alg);
+struct crypto_alg *crypto_alg_mod_lookup(const char *name, u32 type, u32 mask);
+
+struct crypto_larval *crypto_larval_alloc(const char *name, u32 type, u32 mask);
+void crypto_schedule_test(struct crypto_larval *larval);
+void crypto_alg_tested(const char *name, int err);
+
+void crypto_remove_spawns(struct crypto_alg *alg, struct list_head *list,
+			  struct crypto_alg *nalg);
+void crypto_remove_final(struct list_head *list);
+void crypto_shoot_alg(struct crypto_alg *alg);
+struct crypto_tfm *__crypto_alloc_tfm(struct crypto_alg *alg, u32 type,
+				      u32 mask);
+void *crypto_create_tfm_node(struct crypto_alg *alg,
+			const struct crypto_type *frontend, int node);
+
+static inline void *crypto_create_tfm(struct crypto_alg *alg,
+			const struct crypto_type *frontend)
+{
+	return crypto_create_tfm_node(alg, frontend, NUMA_NO_NODE);
+}
+
+struct crypto_alg *crypto_find_alg(const char *alg_name,
+				   const struct crypto_type *frontend,
+				   u32 type, u32 mask);
+
+void *crypto_alloc_tfm_node(const char *alg_name,
+		       const struct crypto_type *frontend, u32 type, u32 mask,
+		       int node);
+
+static inline void *crypto_alloc_tfm(const char *alg_name,
+		       const struct crypto_type *frontend, u32 type, u32 mask)
+{
+	return crypto_alloc_tfm_node(alg_name, frontend, type, mask, NUMA_NO_NODE);
+}
+
+int crypto_probing_notify(unsigned long val, void *v);
+
+unsigned int crypto_alg_extsize(struct crypto_alg *alg);
+
+int crypto_type_has_alg(const char *name, const struct crypto_type *frontend,
+			u32 type, u32 mask);
+
+static inline struct crypto_alg *crypto_alg_get(struct crypto_alg *alg)
+{
+	refcount_inc(&alg->cra_refcnt);
+	return alg;
+}
+
+void crypto_destroy_alg(struct crypto_alg *alg);
+
+static inline void crypto_alg_put(struct crypto_alg *alg)
+{
+	if (refcount_dec_and_test(&alg->cra_refcnt))
+		crypto_destroy_alg(alg);
+}
+
+static inline int crypto_tmpl_get(struct crypto_template *tmpl)
+{
+	return try_module_get(tmpl->module);
+}
+
+static inline void crypto_tmpl_put(struct crypto_template *tmpl)
+{
+	module_put(tmpl->module);
+}
+
+static inline int crypto_is_larval(struct crypto_alg *alg)
+{
+	return alg->cra_flags & CRYPTO_ALG_LARVAL;
+}
+
+static inline int crypto_is_dead(struct crypto_alg *alg)
+{
+	return alg->cra_flags & CRYPTO_ALG_DEAD;
+}
+
+static inline int crypto_is_moribund(struct crypto_alg *alg)
+{
+	return alg->cra_flags & (CRYPTO_ALG_DEAD | CRYPTO_ALG_DYING);
+}
+
+static inline void crypto_notify(unsigned long val, void *v)
+{
+	blocking_notifier_call_chain(&crypto_chain, val, v);
+}
+
+static inline void crypto_yield(u32 flags)
+{
+	if (flags & CRYPTO_TFM_REQ_MAY_SLEEP)
+		cond_resched();
+}
+
+static inline int crypto_is_test_larval(struct crypto_larval *larval)
+{
+	return larval->alg.cra_driver_name[0];
+}
+
+#endif	/* _CRYPTO_INTERNAL_H */
+