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, 113 insertions, 0 deletions

diff --git a/drivers/crypto/bcm/util.h b/drivers/crypto/bcm/util.h
new file mode 100644
index 000000000..61c256384
--- /dev/null
+++ b/drivers/crypto/bcm/util.h
@@ -0,0 +1,113 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2016 Broadcom
+ */
+
+#ifndef _UTIL_H
+#define _UTIL_H
+
+#include <linux/kernel.h>
+#include <linux/delay.h>
+
+#include "spu.h"
+
+extern int flow_debug_logging;
+extern int packet_debug_logging;
+extern int debug_logging_sleep;
+
+#ifdef DEBUG
+#define flow_log(...)	                \
+	do {	                              \
+		if (flow_debug_logging) {	        \
+			printk(__VA_ARGS__);	          \
+			if (debug_logging_sleep)	      \
+				msleep(debug_logging_sleep);	\
+		}	                                \
+	} while (0)
+#define flow_dump(msg, var, var_len)	   \
+	do {	                                 \
+		if (flow_debug_logging) {	           \
+			print_hex_dump(KERN_ALERT, msg, DUMP_PREFIX_NONE,  \
+					16, 1, var, var_len, false); \
+				if (debug_logging_sleep)	       \
+					msleep(debug_logging_sleep);   \
+		}                                    \
+	} while (0)
+
+#define packet_log(...)               \
+	do {                                \
+		if (packet_debug_logging) {       \
+			printk(__VA_ARGS__);            \
+			if (debug_logging_sleep)        \
+				msleep(debug_logging_sleep);  \
+		}                                 \
+	} while (0)
+#define packet_dump(msg, var, var_len)   \
+	do {                                   \
+		if (packet_debug_logging) {          \
+			print_hex_dump(KERN_ALERT, msg, DUMP_PREFIX_NONE,  \
+					16, 1, var, var_len, false); \
+			if (debug_logging_sleep)           \
+				msleep(debug_logging_sleep);     \
+		}                                    \
+	} while (0)
+
+void __dump_sg(struct scatterlist *sg, unsigned int skip, unsigned int len);
+
+#define dump_sg(sg, skip, len)     __dump_sg(sg, skip, len)
+
+#else /* !DEBUG_ON */
+
+static inline void flow_log(const char *format, ...)
+{
+}
+
+static inline void flow_dump(const char *msg, const void *var, size_t var_len)
+{
+}
+
+static inline void packet_log(const char *format, ...)
+{
+}
+
+static inline void packet_dump(const char *msg, const void *var, size_t var_len)
+{
+}
+
+static inline void dump_sg(struct scatterlist *sg, unsigned int skip,
+			   unsigned int len)
+{
+}
+
+#endif /* DEBUG_ON */
+
+int spu_sg_at_offset(struct scatterlist *sg, unsigned int skip,
+		     struct scatterlist **sge, unsigned int *sge_offset);
+
+/* Copy sg data, from skip, length len, to dest */
+void sg_copy_part_to_buf(struct scatterlist *src, u8 *dest,
+			 unsigned int len, unsigned int skip);
+/* Copy src into scatterlist from offset, length len */
+void sg_copy_part_from_buf(struct scatterlist *dest, u8 *src,
+			   unsigned int len, unsigned int skip);
+
+int spu_sg_count(struct scatterlist *sg_list, unsigned int skip, int nbytes);
+u32 spu_msg_sg_add(struct scatterlist **to_sg,
+		   struct scatterlist **from_sg, u32 *skip,
+		   u8 from_nents, u32 tot_len);
+
+void add_to_ctr(u8 *ctr_pos, unsigned int increment);
+
+/* produce a message digest from data of length n bytes */
+int do_shash(unsigned char *name, unsigned char *result,
+	     const u8 *data1, unsigned int data1_len,
+	     const u8 *data2, unsigned int data2_len,
+	     const u8 *key, unsigned int key_len);
+
+char *spu_alg_name(enum spu_cipher_alg alg, enum spu_cipher_mode mode);
+
+void spu_setup_debugfs(void);
+void spu_free_debugfs(void);
+void format_value_ccm(unsigned int val, u8 *buf, u8 len);
+
+#endif