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, 236 insertions, 0 deletions

diff --git a/sound/usb/proc.c b/sound/usb/proc.c
new file mode 100644
index 000000000..f4b7a7ff3
--- /dev/null
+++ b/sound/usb/proc.c
@@ -0,0 +1,236 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ */
+
+#include <linux/init.h>
+#include <linux/usb.h>
+
+#include <sound/core.h>
+#include <sound/info.h>
+#include <sound/pcm.h>
+
+#include "usbaudio.h"
+#include "helper.h"
+#include "card.h"
+#include "endpoint.h"
+#include "proc.h"
+
+/* convert our full speed USB rate into sampling rate in Hz */
+static inline unsigned get_full_speed_hz(unsigned int usb_rate)
+{
+	return (usb_rate * 125 + (1 << 12)) >> 13;
+}
+
+/* convert our high speed USB rate into sampling rate in Hz */
+static inline unsigned get_high_speed_hz(unsigned int usb_rate)
+{
+	return (usb_rate * 125 + (1 << 9)) >> 10;
+}
+
+/*
+ * common proc files to show the usb device info
+ */
+static void proc_audio_usbbus_read(struct snd_info_entry *entry, struct snd_info_buffer *buffer)
+{
+	struct snd_usb_audio *chip = entry->private_data;
+	if (!atomic_read(&chip->shutdown))
+		snd_iprintf(buffer, "%03d/%03d\n", chip->dev->bus->busnum, chip->dev->devnum);
+}
+
+static void proc_audio_usbid_read(struct snd_info_entry *entry, struct snd_info_buffer *buffer)
+{
+	struct snd_usb_audio *chip = entry->private_data;
+	if (!atomic_read(&chip->shutdown))
+		snd_iprintf(buffer, "%04x:%04x\n", 
+			    USB_ID_VENDOR(chip->usb_id),
+			    USB_ID_PRODUCT(chip->usb_id));
+}
+
+void snd_usb_audio_create_proc(struct snd_usb_audio *chip)
+{
+	snd_card_ro_proc_new(chip->card, "usbbus", chip,
+			     proc_audio_usbbus_read);
+	snd_card_ro_proc_new(chip->card, "usbid", chip,
+			     proc_audio_usbid_read);
+}
+
+static const char * const channel_labels[] = {
+	[SNDRV_CHMAP_NA]	= "N/A",
+	[SNDRV_CHMAP_MONO]	= "MONO",
+	[SNDRV_CHMAP_FL]	= "FL",
+	[SNDRV_CHMAP_FR]	= "FR",
+	[SNDRV_CHMAP_FC]	= "FC",
+	[SNDRV_CHMAP_LFE]	= "LFE",
+	[SNDRV_CHMAP_RL]	= "RL",
+	[SNDRV_CHMAP_RR]	= "RR",
+	[SNDRV_CHMAP_FLC]	= "FLC",
+	[SNDRV_CHMAP_FRC]	= "FRC",
+	[SNDRV_CHMAP_RC]	= "RC",
+	[SNDRV_CHMAP_SL]	= "SL",
+	[SNDRV_CHMAP_SR]	= "SR",
+	[SNDRV_CHMAP_TC]	= "TC",
+	[SNDRV_CHMAP_TFL]	= "TFL",
+	[SNDRV_CHMAP_TFC]	= "TFC",
+	[SNDRV_CHMAP_TFR]	= "TFR",
+	[SNDRV_CHMAP_TRL]	= "TRL",
+	[SNDRV_CHMAP_TRC]	= "TRC",
+	[SNDRV_CHMAP_TRR]	= "TRR",
+	[SNDRV_CHMAP_TFLC]	= "TFLC",
+	[SNDRV_CHMAP_TFRC]	= "TFRC",
+	[SNDRV_CHMAP_LLFE]	= "LLFE",
+	[SNDRV_CHMAP_RLFE]	= "RLFE",
+	[SNDRV_CHMAP_TSL]	= "TSL",
+	[SNDRV_CHMAP_TSR]	= "TSR",
+	[SNDRV_CHMAP_BC]	= "BC",
+	[SNDRV_CHMAP_RLC]	= "RLC",
+	[SNDRV_CHMAP_RRC]	= "RRC",
+};
+
+/*
+ * proc interface for list the supported pcm formats
+ */
+static void proc_dump_substream_formats(struct snd_usb_substream *subs, struct snd_info_buffer *buffer)
+{
+	struct audioformat *fp;
+	static const char * const sync_types[4] = {
+		"NONE", "ASYNC", "ADAPTIVE", "SYNC"
+	};
+
+	list_for_each_entry(fp, &subs->fmt_list, list) {
+		snd_pcm_format_t fmt;
+
+		snd_iprintf(buffer, "  Interface %d\n", fp->iface);
+		snd_iprintf(buffer, "    Altset %d\n", fp->altsetting);
+		snd_iprintf(buffer, "    Format:");
+		pcm_for_each_format(fmt)
+			if (fp->formats & pcm_format_to_bits(fmt))
+				snd_iprintf(buffer, " %s",
+					    snd_pcm_format_name(fmt));
+		snd_iprintf(buffer, "\n");
+		snd_iprintf(buffer, "    Channels: %d\n", fp->channels);
+		snd_iprintf(buffer, "    Endpoint: 0x%02x (%d %s) (%s)\n",
+			    fp->endpoint,
+			    fp->endpoint & USB_ENDPOINT_NUMBER_MASK,
+			    fp->endpoint & USB_DIR_IN ? "IN" : "OUT",
+			    sync_types[(fp->ep_attr & USB_ENDPOINT_SYNCTYPE) >> 2]);
+		if (fp->rates & SNDRV_PCM_RATE_CONTINUOUS) {
+			snd_iprintf(buffer, "    Rates: %d - %d (continuous)\n",
+				    fp->rate_min, fp->rate_max);
+		} else {
+			unsigned int i;
+			snd_iprintf(buffer, "    Rates: ");
+			for (i = 0; i < fp->nr_rates; i++) {
+				if (i > 0)
+					snd_iprintf(buffer, ", ");
+				snd_iprintf(buffer, "%d", fp->rate_table[i]);
+			}
+			snd_iprintf(buffer, "\n");
+		}
+		if (subs->speed != USB_SPEED_FULL)
+			snd_iprintf(buffer, "    Data packet interval: %d us\n",
+				    125 * (1 << fp->datainterval));
+		snd_iprintf(buffer, "    Bits: %d\n", fp->fmt_bits);
+
+		if (fp->dsd_raw)
+			snd_iprintf(buffer, "    DSD raw: DOP=%d, bitrev=%d\n",
+				    fp->dsd_dop, fp->dsd_bitrev);
+
+		if (fp->chmap) {
+			const struct snd_pcm_chmap_elem *map = fp->chmap;
+			int c;
+
+			snd_iprintf(buffer, "    Channel map:");
+			for (c = 0; c < map->channels; c++) {
+				if (map->map[c] >= ARRAY_SIZE(channel_labels) ||
+				    !channel_labels[map->map[c]])
+					snd_iprintf(buffer, " --");
+				else
+					snd_iprintf(buffer, " %s",
+						    channel_labels[map->map[c]]);
+			}
+			snd_iprintf(buffer, "\n");
+		}
+
+		if (fp->sync_ep) {
+			snd_iprintf(buffer, "    Sync Endpoint: 0x%02x (%d %s)\n",
+				    fp->sync_ep,
+				    fp->sync_ep & USB_ENDPOINT_NUMBER_MASK,
+				    fp->sync_ep & USB_DIR_IN ? "IN" : "OUT");
+			snd_iprintf(buffer, "    Sync EP Interface: %d\n",
+				    fp->sync_iface);
+			snd_iprintf(buffer, "    Sync EP Altset: %d\n",
+				    fp->sync_altsetting);
+			snd_iprintf(buffer, "    Implicit Feedback Mode: %s\n",
+				    fp->implicit_fb ? "Yes" : "No");
+		}
+
+		// snd_iprintf(buffer, "    Max Packet Size = %d\n", fp->maxpacksize);
+		// snd_iprintf(buffer, "    EP Attribute = %#x\n", fp->attributes);
+	}
+}
+
+static void proc_dump_ep_status(struct snd_usb_substream *subs,
+				struct snd_usb_endpoint *data_ep,
+				struct snd_usb_endpoint *sync_ep,
+				struct snd_info_buffer *buffer)
+{
+	if (!data_ep)
+		return;
+	snd_iprintf(buffer, "    Packet Size = %d\n", data_ep->curpacksize);
+	snd_iprintf(buffer, "    Momentary freq = %u Hz (%#x.%04x)\n",
+		    subs->speed == USB_SPEED_FULL
+		    ? get_full_speed_hz(data_ep->freqm)
+		    : get_high_speed_hz(data_ep->freqm),
+		    data_ep->freqm >> 16, data_ep->freqm & 0xffff);
+	if (sync_ep && data_ep->freqshift != INT_MIN) {
+		int res = 16 - data_ep->freqshift;
+		snd_iprintf(buffer, "    Feedback Format = %d.%d\n",
+			    (sync_ep->syncmaxsize > 3 ? 32 : 24) - res, res);
+	}
+}
+
+static void proc_dump_substream_status(struct snd_usb_audio *chip,
+				       struct snd_usb_substream *subs,
+				       struct snd_info_buffer *buffer)
+{
+	guard(mutex)(&chip->mutex);
+	if (subs->running) {
+		snd_iprintf(buffer, "  Status: Running\n");
+		if (subs->cur_audiofmt) {
+			snd_iprintf(buffer, "    Interface = %d\n", subs->cur_audiofmt->iface);
+			snd_iprintf(buffer, "    Altset = %d\n", subs->cur_audiofmt->altsetting);
+		}
+		proc_dump_ep_status(subs, subs->data_endpoint, subs->sync_endpoint, buffer);
+	} else {
+		snd_iprintf(buffer, "  Status: Stop\n");
+	}
+}
+
+static void proc_pcm_format_read(struct snd_info_entry *entry, struct snd_info_buffer *buffer)
+{
+	struct snd_usb_stream *stream = entry->private_data;
+	struct snd_usb_audio *chip = stream->chip;
+
+	snd_iprintf(buffer, "%s : %s\n", chip->card->longname, stream->pcm->name);
+
+	if (stream->substream[SNDRV_PCM_STREAM_PLAYBACK].num_formats) {
+		snd_iprintf(buffer, "\nPlayback:\n");
+		proc_dump_substream_status(chip, &stream->substream[SNDRV_PCM_STREAM_PLAYBACK], buffer);
+		proc_dump_substream_formats(&stream->substream[SNDRV_PCM_STREAM_PLAYBACK], buffer);
+	}
+	if (stream->substream[SNDRV_PCM_STREAM_CAPTURE].num_formats) {
+		snd_iprintf(buffer, "\nCapture:\n");
+		proc_dump_substream_status(chip, &stream->substream[SNDRV_PCM_STREAM_CAPTURE], buffer);
+		proc_dump_substream_formats(&stream->substream[SNDRV_PCM_STREAM_CAPTURE], buffer);
+	}
+}
+
+void snd_usb_proc_pcm_format_add(struct snd_usb_stream *stream)
+{
+	char name[32];
+	struct snd_card *card = stream->chip->card;
+
+	scnprintf(name, sizeof(name), "stream%d", stream->pcm_index);
+	snd_card_ro_proc_new(card, name, stream, proc_pcm_format_read);
+}
+