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, 352 insertions, 0 deletions

diff --git a/drivers/input/misc/sparcspkr.c b/drivers/input/misc/sparcspkr.c
new file mode 100644
index 000000000..1cfadd738
--- /dev/null
+++ b/drivers/input/misc/sparcspkr.c
@@ -0,0 +1,352 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  Driver for PC-speaker like devices found on various Sparc systems.
+ *
+ *  Copyright (c) 2002 Vojtech Pavlik
+ *  Copyright (c) 2002, 2006, 2008 David S. Miller (davem@davemloft.net)
+ */
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/input.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#include <asm/io.h>
+
+MODULE_AUTHOR("David S. Miller <davem@davemloft.net>");
+MODULE_DESCRIPTION("Sparc Speaker beeper driver");
+MODULE_LICENSE("GPL");
+
+struct grover_beep_info {
+	void __iomem	*freq_regs;
+	void __iomem	*enable_reg;
+};
+
+struct bbc_beep_info {
+	u32		clock_freq;
+	void __iomem	*regs;
+};
+
+struct sparcspkr_state {
+	const char		*name;
+	int (*event)(struct input_dev *dev, unsigned int type, unsigned int code, int value);
+	spinlock_t		lock;
+	struct input_dev	*input_dev;
+	union {
+		struct grover_beep_info grover;
+		struct bbc_beep_info bbc;
+	} u;
+};
+
+static u32 bbc_count_to_reg(struct bbc_beep_info *info, unsigned int count)
+{
+	u32 val, clock_freq = info->clock_freq;
+	int i;
+
+	if (!count)
+		return 0;
+
+	if (count <= clock_freq >> 20)
+		return 1 << 18;
+
+	if (count >= clock_freq >> 12)
+		return 1 << 10;
+
+	val = 1 << 18;
+	for (i = 19; i >= 11; i--) {
+		val >>= 1;
+		if (count <= clock_freq >> i)
+			break;
+	}
+
+	return val;
+}
+
+static int bbc_spkr_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
+{
+	struct sparcspkr_state *state = dev_get_drvdata(dev->dev.parent);
+	struct bbc_beep_info *info = &state->u.bbc;
+	unsigned int count = 0;
+
+	if (type != EV_SND)
+		return -1;
+
+	switch (code) {
+	case SND_BELL:
+		if (value)
+			value = 1000;
+		break;
+	case SND_TONE:
+		break;
+	default:
+		return -1;
+	}
+
+	if (value > 20 && value < 32767)
+		count = 1193182 / value;
+
+	count = bbc_count_to_reg(info, count);
+
+	guard(spinlock_irqsave)(&state->lock);
+
+	if (count) {
+		sbus_writeb(0x01,                 info->regs + 0);
+		sbus_writeb(0x00,                 info->regs + 2);
+		sbus_writeb((count >> 16) & 0xff, info->regs + 3);
+		sbus_writeb((count >>  8) & 0xff, info->regs + 4);
+		sbus_writeb(0x00,                 info->regs + 5);
+	} else {
+		sbus_writeb(0x00,                 info->regs + 0);
+	}
+
+	return 0;
+}
+
+static int grover_spkr_event(struct input_dev *dev, unsigned int type, unsigned int code, int value)
+{
+	struct sparcspkr_state *state = dev_get_drvdata(dev->dev.parent);
+	struct grover_beep_info *info = &state->u.grover;
+	unsigned int count = 0;
+
+	if (type != EV_SND)
+		return -1;
+
+	switch (code) {
+	case SND_BELL:
+		if (value)
+			value = 1000;
+		break;
+	case SND_TONE:
+		break;
+	default:
+		return -1;
+	}
+
+	if (value > 20 && value < 32767)
+		count = 1193182 / value;
+
+	guard(spinlock_irqsave)(&state->lock);
+
+	if (count) {
+		/* enable counter 2 */
+		sbus_writeb(sbus_readb(info->enable_reg) | 3, info->enable_reg);
+		/* set command for counter 2, 2 byte write */
+		sbus_writeb(0xB6, info->freq_regs + 1);
+		/* select desired HZ */
+		sbus_writeb(count & 0xff, info->freq_regs + 0);
+		sbus_writeb((count >> 8) & 0xff, info->freq_regs + 0);
+	} else {
+		/* disable counter 2 */
+		sbus_writeb(sbus_readb(info->enable_reg) & 0xFC, info->enable_reg);
+	}
+
+	return 0;
+}
+
+static int sparcspkr_probe(struct device *dev)
+{
+	struct sparcspkr_state *state = dev_get_drvdata(dev);
+	struct input_dev *input_dev;
+	int error;
+
+	input_dev = input_allocate_device();
+	if (!input_dev)
+		return -ENOMEM;
+
+	input_dev->name = state->name;
+	input_dev->phys = "sparc/input0";
+	input_dev->id.bustype = BUS_ISA;
+	input_dev->id.vendor = 0x001f;
+	input_dev->id.product = 0x0001;
+	input_dev->id.version = 0x0100;
+	input_dev->dev.parent = dev;
+
+	input_dev->evbit[0] = BIT_MASK(EV_SND);
+	input_dev->sndbit[0] = BIT_MASK(SND_BELL) | BIT_MASK(SND_TONE);
+
+	input_dev->event = state->event;
+
+	error = input_register_device(input_dev);
+	if (error) {
+		input_free_device(input_dev);
+		return error;
+	}
+
+	state->input_dev = input_dev;
+
+	return 0;
+}
+
+static void sparcspkr_shutdown(struct platform_device *dev)
+{
+	struct sparcspkr_state *state = platform_get_drvdata(dev);
+	struct input_dev *input_dev = state->input_dev;
+
+	/* turn off the speaker */
+	state->event(input_dev, EV_SND, SND_BELL, 0);
+}
+
+static int bbc_beep_probe(struct platform_device *op)
+{
+	struct sparcspkr_state *state;
+	struct bbc_beep_info *info;
+	int err;
+
+	state = devm_kzalloc(&op->dev, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return -ENOMEM;
+
+	state->name = "Sparc BBC Speaker";
+	state->event = bbc_spkr_event;
+	spin_lock_init(&state->lock);
+
+	struct device_node *dp __free(device_node) = of_find_node_by_path("/");
+	if (!dp)
+		return -ENODEV;
+
+	info = &state->u.bbc;
+	info->clock_freq = of_getintprop_default(dp, "clock-frequency", 0);
+	if (!info->clock_freq)
+		return -ENODEV;
+
+	info->regs = of_ioremap(&op->resource[0], 0, 6, "bbc beep");
+	if (!info->regs)
+		return -ENODEV;
+
+	platform_set_drvdata(op, state);
+
+	err = sparcspkr_probe(&op->dev);
+	if (err) {
+		of_iounmap(&op->resource[0], info->regs, 6);
+		return err;
+	}
+
+	return 0;
+}
+
+static void bbc_remove(struct platform_device *op)
+{
+	struct sparcspkr_state *state = platform_get_drvdata(op);
+	struct input_dev *input_dev = state->input_dev;
+	struct bbc_beep_info *info = &state->u.bbc;
+
+	/* turn off the speaker */
+	state->event(input_dev, EV_SND, SND_BELL, 0);
+
+	input_unregister_device(input_dev);
+
+	of_iounmap(&op->resource[0], info->regs, 6);
+}
+
+static const struct of_device_id bbc_beep_match[] = {
+	{
+		.name = "beep",
+		.compatible = "SUNW,bbc-beep",
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, bbc_beep_match);
+
+static struct platform_driver bbc_beep_driver = {
+	.driver = {
+		.name = "bbcbeep",
+		.of_match_table = bbc_beep_match,
+	},
+	.probe		= bbc_beep_probe,
+	.remove		= bbc_remove,
+	.shutdown	= sparcspkr_shutdown,
+};
+
+static int grover_beep_probe(struct platform_device *op)
+{
+	struct sparcspkr_state *state;
+	struct grover_beep_info *info;
+	int err = -ENOMEM;
+
+	state = devm_kzalloc(&op->dev, sizeof(*state), GFP_KERNEL);
+	if (!state)
+		return err;
+
+	state->name = "Sparc Grover Speaker";
+	state->event = grover_spkr_event;
+	spin_lock_init(&state->lock);
+
+	info = &state->u.grover;
+	info->freq_regs = of_ioremap(&op->resource[2], 0, 2, "grover beep freq");
+	if (!info->freq_regs)
+		return err;
+
+	info->enable_reg = of_ioremap(&op->resource[3], 0, 1, "grover beep enable");
+	if (!info->enable_reg)
+		goto out_unmap_freq_regs;
+
+	platform_set_drvdata(op, state);
+
+	err = sparcspkr_probe(&op->dev);
+	if (err)
+		goto out_clear_drvdata;
+
+	return 0;
+
+out_clear_drvdata:
+	of_iounmap(&op->resource[3], info->enable_reg, 1);
+
+out_unmap_freq_regs:
+	of_iounmap(&op->resource[2], info->freq_regs, 2);
+
+	return err;
+}
+
+static void grover_remove(struct platform_device *op)
+{
+	struct sparcspkr_state *state = platform_get_drvdata(op);
+	struct grover_beep_info *info = &state->u.grover;
+	struct input_dev *input_dev = state->input_dev;
+
+	/* turn off the speaker */
+	state->event(input_dev, EV_SND, SND_BELL, 0);
+
+	input_unregister_device(input_dev);
+
+	of_iounmap(&op->resource[3], info->enable_reg, 1);
+	of_iounmap(&op->resource[2], info->freq_regs, 2);
+}
+
+static const struct of_device_id grover_beep_match[] = {
+	{
+		.name = "beep",
+		.compatible = "SUNW,smbus-beep",
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, grover_beep_match);
+
+static struct platform_driver grover_beep_driver = {
+	.driver = {
+		.name = "groverbeep",
+		.of_match_table = grover_beep_match,
+	},
+	.probe		= grover_beep_probe,
+	.remove		= grover_remove,
+	.shutdown	= sparcspkr_shutdown,
+};
+
+static struct platform_driver * const drivers[] = {
+	&bbc_beep_driver,
+	&grover_beep_driver,
+};
+
+static int __init sparcspkr_init(void)
+{
+	return platform_register_drivers(drivers, ARRAY_SIZE(drivers));
+}
+
+static void __exit sparcspkr_exit(void)
+{
+	platform_unregister_drivers(drivers, ARRAY_SIZE(drivers));
+}
+
+module_init(sparcspkr_init);
+module_exit(sparcspkr_exit);