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, 91 insertions, 0 deletions

diff --git a/include/sound/sdca.h b/include/sound/sdca.h
new file mode 100644
index 000000000..2bdf4e333
--- /dev/null
+++ b/include/sound/sdca.h
@@ -0,0 +1,91 @@
+/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-3-Clause) */
+/*
+ * The MIPI SDCA specification is available for public downloads at
+ * https://www.mipi.org/mipi-sdca-v1-0-download
+ *
+ * Copyright(c) 2024 Intel Corporation
+ */
+
+#ifndef __SDCA_H__
+#define __SDCA_H__
+
+#include <linux/types.h>
+#include <linux/kconfig.h>
+
+struct acpi_table_swft;
+struct fwnode_handle;
+struct sdw_slave;
+struct sdca_dev;
+
+#define SDCA_MAX_FUNCTION_COUNT 8
+
+/**
+ * struct sdca_function_desc - short descriptor for an SDCA Function
+ * @node: firmware node for the Function.
+ * @func_dev: pointer to SDCA function device.
+ * @name: Human-readable string.
+ * @type: Function topology type.
+ * @adr: ACPI address (used for SDCA register access).
+ * @duplicate: Internal flag to indicate if other functions of the same type
+ * exist.
+ */
+struct sdca_function_desc {
+	struct fwnode_handle *node;
+	struct sdca_dev *func_dev;
+	const char *name;
+	u32 type;
+	u8 adr;
+
+	bool duplicate;
+};
+
+/**
+ * struct sdca_device_data - structure containing all SDCA related information
+ * @interface_revision: Value read from _DSD property, mainly to check
+ * for changes between silicon versions.
+ * @num_functions: Total number of supported SDCA functions. Invalid/unsupported
+ * functions will be skipped.
+ * @function: Array of function descriptors.
+ * @swft: Pointer to the SWFT table, if available.
+ */
+struct sdca_device_data {
+	u32 interface_revision;
+	int num_functions;
+	struct sdca_function_desc function[SDCA_MAX_FUNCTION_COUNT];
+	struct acpi_table_swft *swft;
+};
+
+enum sdca_quirk {
+	SDCA_QUIRKS_RT712_VB,
+	SDCA_QUIRKS_SKIP_FUNC_TYPE_PATCHING,
+};
+
+#if IS_ENABLED(CONFIG_ACPI) && IS_ENABLED(CONFIG_SND_SOC_SDCA)
+
+void sdca_lookup_functions(struct sdw_slave *slave);
+void sdca_lookup_swft(struct sdw_slave *slave);
+void sdca_lookup_interface_revision(struct sdw_slave *slave);
+bool sdca_device_quirk_match(struct sdw_slave *slave, enum sdca_quirk quirk);
+int sdca_dev_register_functions(struct sdw_slave *slave);
+void sdca_dev_unregister_functions(struct sdw_slave *slave);
+
+#else
+
+static inline void sdca_lookup_functions(struct sdw_slave *slave) {}
+static inline void sdca_lookup_swft(struct sdw_slave *slave) {}
+static inline void sdca_lookup_interface_revision(struct sdw_slave *slave) {}
+static inline bool sdca_device_quirk_match(struct sdw_slave *slave, enum sdca_quirk quirk)
+{
+	return false;
+}
+
+static inline int sdca_dev_register_functions(struct sdw_slave *slave)
+{
+	return 0;
+}
+
+static inline void sdca_dev_unregister_functions(struct sdw_slave *slave) {}
+
+#endif
+
+#endif