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, 49 insertions, 0 deletions

diff --git a/include/sound/sdw.h b/include/sound/sdw.h
new file mode 100644
index 000000000..6dcdb3228
--- /dev/null
+++ b/include/sound/sdw.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * linux/sound/sdw.h -- SoundWire helpers for ALSA/ASoC
+ *
+ * Copyright (c) 2022 Cirrus Logic Inc.
+ *
+ * Author: Charles Keepax <ckeepax@opensource.cirrus.com>
+ */
+
+#include <linux/soundwire/sdw.h>
+#include <sound/asound.h>
+#include <sound/pcm.h>
+#include <sound/pcm_params.h>
+
+#ifndef __INCLUDE_SOUND_SDW_H
+#define __INCLUDE_SOUND_SDW_H
+
+/**
+ * snd_sdw_params_to_config() - Conversion from hw_params to SoundWire config
+ *
+ * @substream: Pointer to the PCM substream structure
+ * @params: Pointer to the hardware params structure
+ * @stream_config: Stream configuration for the SoundWire audio stream
+ * @port_config: Port configuration for the SoundWire audio stream
+ *
+ * This function provides a basic conversion from the hw_params structure to
+ * SoundWire configuration structures. The user will at a minimum need to also
+ * set the port number in the port config, but may also override more of the
+ * setup, or in the case of a complex user, not use this helper at all and
+ * open-code everything.
+ */
+static inline void snd_sdw_params_to_config(struct snd_pcm_substream *substream,
+					    struct snd_pcm_hw_params *params,
+					    struct sdw_stream_config *stream_config,
+					    struct sdw_port_config *port_config)
+{
+	stream_config->frame_rate = params_rate(params);
+	stream_config->ch_count = params_channels(params);
+	stream_config->bps = snd_pcm_format_width(params_format(params));
+
+	if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK)
+		stream_config->direction = SDW_DATA_DIR_RX;
+	else
+		stream_config->direction = SDW_DATA_DIR_TX;
+
+	port_config->ch_mask = GENMASK(stream_config->ch_count - 1, 0);
+}
+
+#endif