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, 266 insertions, 0 deletions

diff --git a/sound/firewire/fireface/ff.c b/sound/firewire/fireface/ff.c
new file mode 100644
index 000000000..13472822d
--- /dev/null
+++ b/sound/firewire/fireface/ff.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ff.c - a part of driver for RME Fireface series
+ *
+ * Copyright (c) 2015-2017 Takashi Sakamoto
+ */
+
+#include "ff.h"
+
+#define OUI_RME	0x000a35
+
+MODULE_DESCRIPTION("RME Fireface series Driver");
+MODULE_AUTHOR("Takashi Sakamoto <o-takashi@sakamocchi.jp>");
+MODULE_LICENSE("GPL");
+
+static void name_card(struct snd_ff *ff)
+{
+	struct fw_device *fw_dev = fw_parent_device(ff->unit);
+	static const char *const names[] = {
+		[SND_FF_UNIT_VERSION_FF800]	= "Fireface800",
+		[SND_FF_UNIT_VERSION_FF400]	= "Fireface400",
+		[SND_FF_UNIT_VERSION_UFX]	= "FirefaceUFX",
+		[SND_FF_UNIT_VERSION_UCX]	= "FirefaceUCX",
+		[SND_FF_UNIT_VERSION_802]	= "Fireface802",
+	};
+	const char *name;
+
+	name = names[ff->unit_version];
+
+	strscpy(ff->card->driver, "Fireface");
+	strscpy(ff->card->shortname, name);
+	strscpy(ff->card->mixername, name);
+	snprintf(ff->card->longname, sizeof(ff->card->longname),
+		 "RME %s, GUID %08x%08x at %s, S%d", name,
+		 fw_dev->config_rom[3], fw_dev->config_rom[4],
+		 dev_name(&ff->unit->device), 100 << fw_dev->max_speed);
+}
+
+static void ff_card_free(struct snd_card *card)
+{
+	struct snd_ff *ff = card->private_data;
+
+	snd_ff_stream_destroy_duplex(ff);
+	snd_ff_transaction_unregister(ff);
+
+	kfree(ff->msg_parser);
+
+	mutex_destroy(&ff->mutex);
+	fw_unit_put(ff->unit);
+}
+
+static int snd_ff_probe(struct fw_unit *unit, const struct ieee1394_device_id *entry)
+{
+	struct snd_card *card;
+	struct snd_ff *ff;
+	int err;
+
+	err = snd_card_new(&unit->device, -1, NULL, THIS_MODULE, sizeof(*ff), &card);
+	if (err < 0)
+		return err;
+	card->private_free = ff_card_free;
+
+	ff = card->private_data;
+	ff->unit = fw_unit_get(unit);
+	dev_set_drvdata(&unit->device, ff);
+	ff->card = card;
+
+	mutex_init(&ff->mutex);
+	spin_lock_init(&ff->lock);
+	init_waitqueue_head(&ff->hwdep_wait);
+
+	ff->unit_version = entry->version;
+	ff->spec = entry->driver_data_ptr;
+
+	err = snd_ff_transaction_register(ff);
+	if (err < 0)
+		goto error;
+
+	name_card(ff);
+
+	err = snd_ff_stream_init_duplex(ff);
+	if (err < 0)
+		goto error;
+
+	snd_ff_proc_init(ff);
+
+	err = snd_ff_create_midi_devices(ff);
+	if (err < 0)
+		goto error;
+
+	err = snd_ff_create_pcm_devices(ff);
+	if (err < 0)
+		goto error;
+
+	err = snd_ff_create_hwdep_devices(ff);
+	if (err < 0)
+		goto error;
+
+	if (ff->spec->protocol->msg_parser_size > 0) {
+		ff->msg_parser = kzalloc(ff->spec->protocol->msg_parser_size, GFP_KERNEL);
+		if (!ff->msg_parser) {
+			err = -ENOMEM;
+			goto error;
+		}
+	}
+
+	err = snd_card_register(card);
+	if (err < 0)
+		goto error;
+
+	return 0;
+error:
+	snd_card_free(card);
+	return err;
+}
+
+static void snd_ff_update(struct fw_unit *unit)
+{
+	struct snd_ff *ff = dev_get_drvdata(&unit->device);
+
+	snd_ff_transaction_reregister(ff);
+
+	snd_ff_stream_update_duplex(ff);
+}
+
+static void snd_ff_remove(struct fw_unit *unit)
+{
+	struct snd_ff *ff = dev_get_drvdata(&unit->device);
+
+	// Block till all of ALSA character devices are released.
+	snd_card_free(ff->card);
+}
+
+static const struct snd_ff_spec spec_ff800 = {
+	.pcm_capture_channels = {28, 20, 12},
+	.pcm_playback_channels = {28, 20, 12},
+	.midi_in_ports = 1,
+	.midi_out_ports = 1,
+	.protocol = &snd_ff_protocol_ff800,
+	.midi_high_addr = 0x000200000320ull,
+	.midi_addr_range = 12,
+	.midi_rx_addrs = {0x000080180000ull, 0},
+};
+
+static const struct snd_ff_spec spec_ff400 = {
+	.pcm_capture_channels = {18, 14, 10},
+	.pcm_playback_channels = {18, 14, 10},
+	.midi_in_ports = 2,
+	.midi_out_ports = 2,
+	.protocol = &snd_ff_protocol_ff400,
+	.midi_high_addr = 0x0000801003f4ull,
+	.midi_addr_range = SND_FF_MAXIMIM_MIDI_QUADS * 4,
+	.midi_rx_addrs = {0x000080180000ull, 0x000080190000ull},
+};
+
+static const struct snd_ff_spec spec_ucx = {
+	.pcm_capture_channels = {18, 14, 12},
+	.pcm_playback_channels = {18, 14, 12},
+	.midi_in_ports = 2,
+	.midi_out_ports = 2,
+	.protocol = &snd_ff_protocol_latter,
+	.midi_high_addr = 0xffff00000034ull,
+	.midi_addr_range = 0x80,
+	.midi_rx_addrs = {0xffff00000030ull, 0xffff00000030ull},
+};
+
+static const struct snd_ff_spec spec_ufx_802 = {
+	.pcm_capture_channels = {30, 22, 14},
+	.pcm_playback_channels = {30, 22, 14},
+	.midi_in_ports = 1,
+	.midi_out_ports = 1,
+	.protocol = &snd_ff_protocol_latter,
+	.midi_high_addr = 0xffff00000034ull,
+	.midi_addr_range = 0x80,
+	.midi_rx_addrs = {0xffff00000030ull, 0xffff00000030ull},
+};
+
+static const struct ieee1394_device_id snd_ff_id_table[] = {
+	/* Fireface 800 */
+	{
+		.match_flags	= IEEE1394_MATCH_VENDOR_ID |
+				  IEEE1394_MATCH_SPECIFIER_ID |
+				  IEEE1394_MATCH_VERSION |
+				  IEEE1394_MATCH_MODEL_ID,
+		.vendor_id	= OUI_RME,
+		.specifier_id	= OUI_RME,
+		.version	= SND_FF_UNIT_VERSION_FF800,
+		.model_id	= 0x101800,
+		.driver_data_ptr = &spec_ff800,
+	},
+	/* Fireface 400 */
+	{
+		.match_flags	= IEEE1394_MATCH_VENDOR_ID |
+				  IEEE1394_MATCH_SPECIFIER_ID |
+				  IEEE1394_MATCH_VERSION |
+				  IEEE1394_MATCH_MODEL_ID,
+		.vendor_id	= OUI_RME,
+		.specifier_id	= OUI_RME,
+		.version	= SND_FF_UNIT_VERSION_FF400,
+		.model_id	= 0x101800,
+		.driver_data_ptr = &spec_ff400,
+	},
+	// Fireface UFX.
+	{
+		.match_flags	= IEEE1394_MATCH_VENDOR_ID |
+				  IEEE1394_MATCH_SPECIFIER_ID |
+				  IEEE1394_MATCH_VERSION |
+				  IEEE1394_MATCH_MODEL_ID,
+		.vendor_id	= OUI_RME,
+		.specifier_id	= OUI_RME,
+		.version	= SND_FF_UNIT_VERSION_UFX,
+		.model_id	= 0x101800,
+		.driver_data_ptr = &spec_ufx_802,
+	},
+	// Fireface UCX.
+	{
+		.match_flags	= IEEE1394_MATCH_VENDOR_ID |
+				  IEEE1394_MATCH_SPECIFIER_ID |
+				  IEEE1394_MATCH_VERSION |
+				  IEEE1394_MATCH_MODEL_ID,
+		.vendor_id	= OUI_RME,
+		.specifier_id	= OUI_RME,
+		.version	= SND_FF_UNIT_VERSION_UCX,
+		.model_id	= 0x101800,
+		.driver_data_ptr = &spec_ucx,
+	},
+	// Fireface 802.
+	{
+		.match_flags	= IEEE1394_MATCH_VENDOR_ID |
+				  IEEE1394_MATCH_SPECIFIER_ID |
+				  IEEE1394_MATCH_VERSION |
+				  IEEE1394_MATCH_MODEL_ID,
+		.vendor_id	= OUI_RME,
+		.specifier_id	= OUI_RME,
+		.version	= SND_FF_UNIT_VERSION_802,
+		.model_id	= 0x101800,
+		.driver_data_ptr = &spec_ufx_802,
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(ieee1394, snd_ff_id_table);
+
+static struct fw_driver ff_driver = {
+	.driver = {
+		.owner	= THIS_MODULE,
+		.name	= KBUILD_MODNAME,
+		.bus	= &fw_bus_type,
+	},
+	.probe    = snd_ff_probe,
+	.update   = snd_ff_update,
+	.remove   = snd_ff_remove,
+	.id_table = snd_ff_id_table,
+};
+
+static int __init snd_ff_init(void)
+{
+	return driver_register(&ff_driver.driver);
+}
+
+static void __exit snd_ff_exit(void)
+{
+	driver_unregister(&ff_driver.driver);
+}
+
+module_init(snd_ff_init);
+module_exit(snd_ff_exit);