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, 80 insertions, 0 deletions

diff --git a/include/scsi/scsi_dbg.h b/include/scsi/scsi_dbg.h
new file mode 100644
index 000000000..efcdc7853
--- /dev/null
+++ b/include/scsi/scsi_dbg.h
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SCSI_SCSI_DBG_H
+#define _SCSI_SCSI_DBG_H
+
+struct scsi_cmnd;
+struct scsi_device;
+struct scsi_sense_hdr;
+
+extern void scsi_print_command(struct scsi_cmnd *);
+extern size_t __scsi_format_command(char *, size_t,
+				   const unsigned char *, size_t);
+extern void scsi_print_sense_hdr(const struct scsi_device *, const char *,
+				 const struct scsi_sense_hdr *);
+extern void scsi_print_sense(struct scsi_cmnd *);
+extern void __scsi_print_sense(const struct scsi_device *, const char *name,
+			       const unsigned char *sense_buffer,
+			       int sense_len);
+extern void scsi_print_result(struct scsi_cmnd *, const char *, int);
+
+#ifdef CONFIG_SCSI_CONSTANTS
+extern bool scsi_opcode_sa_name(int, int, const char **, const char **);
+extern const char *scsi_sense_key_string(unsigned char);
+extern const char *scsi_extd_sense_format(unsigned char, unsigned char,
+					  const char **);
+extern const char *scsi_mlreturn_string(int);
+extern const char *scsi_hostbyte_string(int);
+#else
+static inline bool
+scsi_opcode_sa_name(int cmd, int sa,
+		    const char **cdb_name, const char **sa_name)
+{
+	*cdb_name = NULL;
+	switch (cmd) {
+	case VARIABLE_LENGTH_CMD:
+	case MAINTENANCE_IN:
+	case MAINTENANCE_OUT:
+	case PERSISTENT_RESERVE_IN:
+	case PERSISTENT_RESERVE_OUT:
+	case SERVICE_ACTION_IN_12:
+	case SERVICE_ACTION_OUT_12:
+	case SERVICE_ACTION_BIDIRECTIONAL:
+	case SERVICE_ACTION_IN_16:
+	case SERVICE_ACTION_OUT_16:
+	case EXTENDED_COPY:
+	case RECEIVE_COPY_RESULTS:
+		*sa_name = NULL;
+		return true;
+	default:
+		return false;
+	}
+}
+
+static inline const char *
+scsi_sense_key_string(unsigned char key)
+{
+	return NULL;
+}
+
+static inline const char *
+scsi_extd_sense_format(unsigned char asc, unsigned char ascq, const char **fmt)
+{
+	*fmt = NULL;
+	return NULL;
+}
+
+static inline const char *
+scsi_mlreturn_string(int result)
+{
+	return NULL;
+}
+
+static inline const char *
+scsi_hostbyte_string(int result)
+{
+	return NULL;
+}
+
+#endif
+
+#endif /* _SCSI_SCSI_DBG_H */