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, 190 insertions, 0 deletions

diff --git a/sound/ppc/powermac.c b/sound/ppc/powermac.c
new file mode 100644
index 000000000..e685d2458
--- /dev/null
+++ b/sound/ppc/powermac.c
@@ -0,0 +1,190 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Driver for PowerMac AWACS
+ * Copyright (c) 2001 by Takashi Iwai <tiwai@suse.de>
+ *   based on dmasound.c.
+ */
+
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <sound/core.h>
+#include <sound/initval.h>
+#include "pmac.h"
+#include "awacs.h"
+#include "burgundy.h"
+
+#define CHIP_NAME "PMac"
+
+MODULE_DESCRIPTION("PowerMac");
+MODULE_LICENSE("GPL");
+
+static int index = SNDRV_DEFAULT_IDX1;		/* Index 0-MAX */
+static char *id = SNDRV_DEFAULT_STR1;		/* ID for this card */
+static bool enable_beep = 1;
+
+module_param(index, int, 0444);
+MODULE_PARM_DESC(index, "Index value for " CHIP_NAME " soundchip.");
+module_param(id, charp, 0444);
+MODULE_PARM_DESC(id, "ID string for " CHIP_NAME " soundchip.");
+module_param(enable_beep, bool, 0444);
+MODULE_PARM_DESC(enable_beep, "Enable beep using PCM.");
+
+static struct platform_device *device;
+
+
+/*
+ */
+
+static int snd_pmac_probe(struct platform_device *devptr)
+{
+	struct snd_card *card;
+	struct snd_pmac *chip;
+	char *name_ext;
+	int err;
+
+	err = snd_card_new(&devptr->dev, index, id, THIS_MODULE, 0, &card);
+	if (err < 0)
+		return err;
+
+	err = snd_pmac_new(card, &chip);
+	if (err < 0)
+		goto __error;
+	card->private_data = chip;
+
+	switch (chip->model) {
+	case PMAC_BURGUNDY:
+		strscpy(card->driver, "PMac Burgundy");
+		strscpy(card->shortname, "PowerMac Burgundy");
+		sprintf(card->longname, "%s (Dev %d) Sub-frame %d",
+			card->shortname, chip->device_id, chip->subframe);
+		err = snd_pmac_burgundy_init(chip);
+		if (err < 0)
+			goto __error;
+		break;
+	case PMAC_DACA:
+		strscpy(card->driver, "PMac DACA");
+		strscpy(card->shortname, "PowerMac DACA");
+		sprintf(card->longname, "%s (Dev %d) Sub-frame %d",
+			card->shortname, chip->device_id, chip->subframe);
+		err = snd_pmac_daca_init(chip);
+		if (err < 0)
+			goto __error;
+		break;
+	case PMAC_TUMBLER:
+	case PMAC_SNAPPER:
+		name_ext = chip->model == PMAC_TUMBLER ? "Tumbler" : "Snapper";
+		sprintf(card->driver, "PMac %s", name_ext);
+		sprintf(card->shortname, "PowerMac %s", name_ext);
+		sprintf(card->longname, "%s (Dev %d) Sub-frame %d",
+			card->shortname, chip->device_id, chip->subframe);
+		err = snd_pmac_tumbler_init(chip);
+		if (err < 0)
+			goto __error;
+		err = snd_pmac_tumbler_post_init();
+		if (err < 0)
+			goto __error;
+		break;
+	case PMAC_AWACS:
+	case PMAC_SCREAMER:
+		name_ext = chip->model == PMAC_SCREAMER ? "Screamer" : "AWACS";
+		sprintf(card->driver, "PMac %s", name_ext);
+		sprintf(card->shortname, "PowerMac %s", name_ext);
+		if (chip->is_pbook_3400)
+			name_ext = " [PB3400]";
+		else if (chip->is_pbook_G3)
+			name_ext = " [PBG3]";
+		else
+			name_ext = "";
+		sprintf(card->longname, "%s%s Rev %d",
+			card->shortname, name_ext, chip->revision);
+		err = snd_pmac_awacs_init(chip);
+		if (err < 0)
+			goto __error;
+		break;
+	default:
+		dev_err(&devptr->dev, "unsupported hardware %d\n", chip->model);
+		err = -EINVAL;
+		goto __error;
+	}
+
+	err = snd_pmac_pcm_new(chip);
+	if (err < 0)
+		goto __error;
+
+	chip->initialized = 1;
+	if (enable_beep)
+		snd_pmac_attach_beep(chip);
+
+	err = snd_card_register(card);
+	if (err < 0)
+		goto __error;
+
+	platform_set_drvdata(devptr, card);
+	return 0;
+
+__error:
+	snd_card_free(card);
+	return err;
+}
+
+
+static void snd_pmac_remove(struct platform_device *devptr)
+{
+	snd_card_free(platform_get_drvdata(devptr));
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int snd_pmac_driver_suspend(struct device *dev)
+{
+	struct snd_card *card = dev_get_drvdata(dev);
+	snd_pmac_suspend(card->private_data);
+	return 0;
+}
+
+static int snd_pmac_driver_resume(struct device *dev)
+{
+	struct snd_card *card = dev_get_drvdata(dev);
+	snd_pmac_resume(card->private_data);
+	return 0;
+}
+
+static SIMPLE_DEV_PM_OPS(snd_pmac_pm, snd_pmac_driver_suspend, snd_pmac_driver_resume);
+#define SND_PMAC_PM_OPS	&snd_pmac_pm
+#else
+#define SND_PMAC_PM_OPS	NULL
+#endif
+
+#define SND_PMAC_DRIVER		"snd_powermac"
+
+static struct platform_driver snd_pmac_driver = {
+	.probe		= snd_pmac_probe,
+	.remove		= snd_pmac_remove,
+	.driver		= {
+		.name	= SND_PMAC_DRIVER,
+		.pm	= SND_PMAC_PM_OPS,
+	},
+};
+
+static int __init alsa_card_pmac_init(void)
+{
+	int err;
+
+	err = platform_driver_register(&snd_pmac_driver);
+	if (err < 0)
+		return err;
+	device = platform_device_register_simple(SND_PMAC_DRIVER, -1, NULL, 0);
+	return 0;
+
+}
+
+static void __exit alsa_card_pmac_exit(void)
+{
+	if (!IS_ERR(device))
+		platform_device_unregister(device);
+	platform_driver_unregister(&snd_pmac_driver);
+}
+
+module_init(alsa_card_pmac_init)
+module_exit(alsa_card_pmac_exit)