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, 93 insertions, 0 deletions

diff --git a/include/sound/cs-amp-lib.h b/include/sound/cs-amp-lib.h
new file mode 100644
index 000000000..e9aa86d76
--- /dev/null
+++ b/include/sound/cs-amp-lib.h
@@ -0,0 +1,93 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2024 Cirrus Logic, Inc. and
+ *                    Cirrus Logic International Semiconductor Ltd.
+ */
+
+#ifndef CS_AMP_LIB_H
+#define CS_AMP_LIB_H
+
+#include <linux/efi.h>
+#include <linux/types.h>
+
+struct cs_dsp;
+
+struct cirrus_amp_cal_data {
+	u32 calTarget[2];
+	u32 calTime[2];
+	s8  calAmbient;
+	u8  calStatus;
+	u16 calR;
+} __packed;
+
+struct cirrus_amp_efi_data {
+	u32 size;
+	u32 count;
+	struct cirrus_amp_cal_data data[] __counted_by(count);
+} __packed;
+
+/**
+ * struct cirrus_amp_cal_controls - definition of firmware calibration controls
+ * @alg_id:	ID of algorithm containing the controls.
+ * @mem_region:	DSP memory region containing the controls.
+ * @ambient:	Name of control for calAmbient value.
+ * @calr:	Name of control for calR value.
+ * @status:	Name of control for calStatus value.
+ * @checksum:	Name of control for checksum value.
+ */
+struct cirrus_amp_cal_controls {
+	unsigned int alg_id;
+	int mem_region;
+	const char *ambient;
+	const char *calr;
+	const char *status;
+	const char *checksum;
+};
+
+int cs_amp_write_cal_coeffs(struct cs_dsp *dsp,
+			    const struct cirrus_amp_cal_controls *controls,
+			    const struct cirrus_amp_cal_data *data);
+int cs_amp_read_cal_coeffs(struct cs_dsp *dsp,
+			   const struct cirrus_amp_cal_controls *controls,
+			   struct cirrus_amp_cal_data *data);
+int cs_amp_write_ambient_temp(struct cs_dsp *dsp,
+			      const struct cirrus_amp_cal_controls *controls,
+			      u32 temp);
+int cs_amp_get_efi_calibration_data(struct device *dev, u64 target_uid, int amp_index,
+				    struct cirrus_amp_cal_data *out_data);
+int cs_amp_set_efi_calibration_data(struct device *dev, int amp_index, int num_amps,
+				    const struct cirrus_amp_cal_data *in_data);
+int cs_amp_get_vendor_spkid(struct device *dev);
+const char *cs_amp_devm_get_vendor_specific_variant_id(struct device *dev,
+						       int ssid_vendor,
+						       int ssid_device);
+struct dentry *cs_amp_create_debugfs(struct device *dev);
+
+static inline u64 cs_amp_cal_target_u64(const struct cirrus_amp_cal_data *data)
+{
+	return ((u64)data->calTarget[1] << 32) | data->calTarget[0];
+}
+
+struct cs_amp_test_hooks {
+	efi_status_t (*get_efi_variable)(efi_char16_t *name,
+					 efi_guid_t *guid,
+					 u32 *returned_attr,
+					 unsigned long *size,
+					 void *buf);
+	efi_status_t (*set_efi_variable)(efi_char16_t *name,
+					 efi_guid_t *guid,
+					 u32 attr,
+					 unsigned long size,
+					 void *buf);
+
+	int (*write_cal_coeff)(struct cs_dsp *dsp,
+			       const struct cirrus_amp_cal_controls *controls,
+			       const char *ctl_name, u32 val);
+
+	int (*read_cal_coeff)(struct cs_dsp *dsp,
+			      const struct cirrus_amp_cal_controls *controls,
+			      const char *ctl_name, u32 *val);
+};
+extern const struct cs_amp_test_hooks * const cs_amp_test_hooks;
+
+#endif /* CS_AMP_LIB_H */