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, 33 insertions, 0 deletions

diff --git a/include/sound/sdca_regmap.h b/include/sound/sdca_regmap.h
new file mode 100644
index 000000000..792540a53
--- /dev/null
+++ b/include/sound/sdca_regmap.h
@@ -0,0 +1,33 @@
+/* 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_REGMAP_H__
+#define __SDCA_REGMAP_H__
+
+struct device;
+struct sdca_function_data;
+struct regmap;
+struct reg_default;
+
+bool sdca_regmap_readable(struct sdca_function_data *function, unsigned int reg);
+bool sdca_regmap_writeable(struct sdca_function_data *function, unsigned int reg);
+bool sdca_regmap_volatile(struct sdca_function_data *function, unsigned int reg);
+bool sdca_regmap_deferrable(struct sdca_function_data *function, unsigned int reg);
+int sdca_regmap_mbq_size(struct sdca_function_data *function, unsigned int reg);
+
+int sdca_regmap_count_constants(struct device *dev, struct sdca_function_data *function);
+int sdca_regmap_populate_constants(struct device *dev, struct sdca_function_data *function,
+				   struct reg_default *consts);
+
+int sdca_regmap_write_defaults(struct device *dev, struct regmap *regmap,
+			       struct sdca_function_data *function);
+int sdca_regmap_write_init(struct device *dev, struct regmap *regmap,
+			   struct sdca_function_data *function);
+
+#endif // __SDCA_REGMAP_H__