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, 107 insertions, 0 deletions

diff --git a/include/sound/sdca_fdl.h b/include/sound/sdca_fdl.h
new file mode 100644
index 000000000..dc33927b8
--- /dev/null
+++ b/include/sound/sdca_fdl.h
@@ -0,0 +1,107 @@
+/* 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_FDL_H__
+#define __SDCA_FDL_H__
+
+#include <linux/completion.h>
+#include <linux/workqueue.h>
+
+struct device;
+struct regmap;
+struct sdca_fdl_set;
+struct sdca_function_data;
+struct sdca_interrupt;
+struct sdca_interrupt_info;
+
+/**
+ * struct fdl_state - FDL state structure to keep data between interrupts
+ * @begin: Completion indicating the start of an FDL download cycle.
+ * @done: Completion indicating the end of an FDL download cycle.
+ * @timeout: Delayed work used for timing out UMP transactions.
+ * @lock: Mutex to protect between the timeout work and IRQ handlers.
+ * @interrupt: Pointer to the interrupt struct to which this FDL is attached.
+ * @set: Pointer to the FDL set currently being downloaded.
+ * @file_index: Index of the current file being processed.
+ */
+struct fdl_state {
+	struct completion begin;
+	struct completion done;
+	struct delayed_work timeout;
+	struct mutex lock;
+
+	struct sdca_interrupt *interrupt;
+	struct sdca_fdl_set *set;
+	int file_index;
+};
+
+#define SDCA_CTL_XU_FDLH_COMPLETE	0
+#define SDCA_CTL_XU_FDLH_MORE_FILES	SDCA_CTL_XU_FDLH_SET_IN_PROGRESS
+#define SDCA_CTL_XU_FDLH_FILE_AVAILABLE	(SDCA_CTL_XU_FDLH_TRANSFERRED_FILE | \
+					 SDCA_CTL_XU_FDLH_SET_IN_PROGRESS)
+#define SDCA_CTL_XU_FDLH_MASK		(SDCA_CTL_XU_FDLH_TRANSFERRED_CHUNK | \
+					 SDCA_CTL_XU_FDLH_TRANSFERRED_FILE | \
+					 SDCA_CTL_XU_FDLH_SET_IN_PROGRESS | \
+					 SDCA_CTL_XU_FDLH_RESET_ACK | \
+					 SDCA_CTL_XU_FDLH_REQ_ABORT)
+
+#define SDCA_CTL_XU_FDLD_COMPLETE	0
+#define SDCA_CTL_XU_FDLD_FILE_OK	(SDCA_CTL_XU_FDLH_TRANSFERRED_FILE | \
+					 SDCA_CTL_XU_FDLH_SET_IN_PROGRESS | \
+					 SDCA_CTL_XU_FDLD_ACK_TRANSFER | \
+					 SDCA_CTL_XU_FDLD_NEEDS_SET)
+#define SDCA_CTL_XU_FDLD_MORE_FILES_OK	(SDCA_CTL_XU_FDLH_SET_IN_PROGRESS | \
+					 SDCA_CTL_XU_FDLD_ACK_TRANSFER | \
+					 SDCA_CTL_XU_FDLD_NEEDS_SET)
+#define SDCA_CTL_XU_FDLD_MASK		(SDCA_CTL_XU_FDLD_REQ_RESET | \
+					 SDCA_CTL_XU_FDLD_REQ_ABORT | \
+					 SDCA_CTL_XU_FDLD_ACK_TRANSFER | \
+					 SDCA_CTL_XU_FDLD_NEEDS_SET)
+
+#if IS_ENABLED(CONFIG_SND_SOC_SDCA_FDL)
+
+int sdca_fdl_alloc_state(struct sdca_interrupt *interrupt);
+void sdca_fdl_free_state(struct sdca_interrupt *interrupt);
+
+int sdca_fdl_process(struct sdca_interrupt *interrupt);
+int sdca_fdl_sync(struct device *dev, struct sdca_function_data *function,
+		  struct sdca_interrupt_info *info);
+
+int sdca_reset_function(struct device *dev, struct sdca_function_data *function,
+			struct regmap *regmap);
+
+#else
+
+static inline int sdca_fdl_alloc_state(struct sdca_interrupt *interrupt)
+{
+	return 0;
+}
+
+static inline int sdca_fdl_process(struct sdca_interrupt *interrupt)
+{
+	return 0;
+}
+
+static inline int sdca_fdl_sync(struct device *dev,
+				struct sdca_function_data *function,
+				struct sdca_interrupt_info *info)
+{
+	return 0;
+}
+
+static inline int sdca_reset_function(struct device *dev,
+				      struct sdca_function_data *function,
+				      struct regmap *regmap)
+{
+	return 0;
+}
+
+#endif // CONFIG_SND_SOC_SDCA_FDL
+
+#endif // __SDCA_FDL_H__