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, 50 insertions, 0 deletions

diff --git a/include/sound/sdca_ump.h b/include/sound/sdca_ump.h
new file mode 100644
index 000000000..f54f9d48c
--- /dev/null
+++ b/include/sound/sdca_ump.h
@@ -0,0 +1,50 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * The MIPI SDCA specification is available for public downloads at
+ * https://www.mipi.org/mipi-sdca-v1-0-download
+ *
+ * Copyright (C) 2025 Cirrus Logic, Inc. and
+ *                    Cirrus Logic International Semiconductor Ltd.
+ */
+
+#ifndef __SDCA_UMP_H__
+#define __SDCA_UMP_H__
+
+struct regmap;
+struct sdca_control;
+struct sdca_entity;
+struct sdca_function_data;
+struct snd_soc_component;
+struct delayed_work;
+
+int sdca_ump_get_owner_host(struct device *dev,
+			    struct regmap *function_regmap,
+			    struct sdca_function_data *function,
+			    struct sdca_entity *entity,
+			    struct sdca_control *control);
+int sdca_ump_set_owner_device(struct device *dev,
+			      struct regmap *function_regmap,
+			      struct sdca_function_data *function,
+			      struct sdca_entity *entity,
+			      struct sdca_control *control);
+int sdca_ump_read_message(struct device *dev,
+			  struct regmap *device_regmap,
+			  struct regmap *function_regmap,
+			  struct sdca_function_data *function,
+			  struct sdca_entity *entity,
+			  unsigned int offset_sel, unsigned int length_sel,
+			  void **msg);
+int sdca_ump_write_message(struct device *dev,
+			   struct regmap *device_regmap,
+			   struct regmap *function_regmap,
+			   struct sdca_function_data *function,
+			   struct sdca_entity *entity,
+			   unsigned int offset_sel, unsigned int msg_offset,
+			   unsigned int length_sel,
+			   void *msg, int msg_len);
+
+void sdca_ump_cancel_timeout(struct delayed_work *work);
+void sdca_ump_schedule_timeout(struct delayed_work *work,
+			       unsigned int timeout_us);
+
+#endif // __SDCA_UMP_H__