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, 217 insertions, 0 deletions

diff --git a/drivers/input/serio/pcips2.c b/drivers/input/serio/pcips2.c
new file mode 100644
index 000000000..78f47b0ca
--- /dev/null
+++ b/drivers/input/serio/pcips2.c
@@ -0,0 +1,217 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * linux/drivers/input/serio/pcips2.c
+ *
+ *  Copyright (C) 2003 Russell King, All Rights Reserved.
+ *
+ *  I'm not sure if this is a generic PS/2 PCI interface or specific to
+ *  the Mobility Electronics docking station.
+ */
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/input.h>
+#include <linux/pci.h>
+#include <linux/slab.h>
+#include <linux/serio.h>
+#include <linux/delay.h>
+#include <asm/io.h>
+
+#define PS2_CTRL		(0)
+#define PS2_STATUS		(1)
+#define PS2_DATA		(2)
+
+#define PS2_CTRL_CLK		(1<<0)
+#define PS2_CTRL_DAT		(1<<1)
+#define PS2_CTRL_TXIRQ		(1<<2)
+#define PS2_CTRL_ENABLE		(1<<3)
+#define PS2_CTRL_RXIRQ		(1<<4)
+
+#define PS2_STAT_CLK		(1<<0)
+#define PS2_STAT_DAT		(1<<1)
+#define PS2_STAT_PARITY		(1<<2)
+#define PS2_STAT_RXFULL		(1<<5)
+#define PS2_STAT_TXBUSY		(1<<6)
+#define PS2_STAT_TXEMPTY	(1<<7)
+
+struct pcips2_data {
+	struct serio	*io;
+	unsigned int	base;
+	struct pci_dev	*dev;
+};
+
+static int pcips2_write(struct serio *io, unsigned char val)
+{
+	struct pcips2_data *ps2if = io->port_data;
+	unsigned int stat;
+
+	do {
+		stat = inb(ps2if->base + PS2_STATUS);
+		cpu_relax();
+	} while (!(stat & PS2_STAT_TXEMPTY));
+
+	outb(val, ps2if->base + PS2_DATA);
+
+	return 0;
+}
+
+static irqreturn_t pcips2_interrupt(int irq, void *devid)
+{
+	struct pcips2_data *ps2if = devid;
+	unsigned char status, scancode;
+	int handled = 0;
+
+	do {
+		unsigned int flag;
+
+		status = inb(ps2if->base + PS2_STATUS);
+		if (!(status & PS2_STAT_RXFULL))
+			break;
+		handled = 1;
+		scancode = inb(ps2if->base + PS2_DATA);
+		if (status == 0xff && scancode == 0xff)
+			break;
+
+		flag = (status & PS2_STAT_PARITY) ? 0 : SERIO_PARITY;
+
+		if (hweight8(scancode) & 1)
+			flag ^= SERIO_PARITY;
+
+		serio_interrupt(ps2if->io, scancode, flag);
+	} while (1);
+	return IRQ_RETVAL(handled);
+}
+
+static void pcips2_flush_input(struct pcips2_data *ps2if)
+{
+	unsigned char status, scancode;
+
+	do {
+		status = inb(ps2if->base + PS2_STATUS);
+		if (!(status & PS2_STAT_RXFULL))
+			break;
+		scancode = inb(ps2if->base + PS2_DATA);
+		if (status == 0xff && scancode == 0xff)
+			break;
+	} while (1);
+}
+
+static int pcips2_open(struct serio *io)
+{
+	struct pcips2_data *ps2if = io->port_data;
+	int ret, val = 0;
+
+	outb(PS2_CTRL_ENABLE, ps2if->base);
+	pcips2_flush_input(ps2if);
+
+	ret = request_irq(ps2if->dev->irq, pcips2_interrupt, IRQF_SHARED,
+			  "pcips2", ps2if);
+	if (ret == 0)
+		val = PS2_CTRL_ENABLE | PS2_CTRL_RXIRQ;
+
+	outb(val, ps2if->base);
+
+	return ret;
+}
+
+static void pcips2_close(struct serio *io)
+{
+	struct pcips2_data *ps2if = io->port_data;
+
+	outb(0, ps2if->base);
+
+	free_irq(ps2if->dev->irq, ps2if);
+}
+
+static int pcips2_probe(struct pci_dev *dev, const struct pci_device_id *id)
+{
+	struct pcips2_data *ps2if;
+	struct serio *serio;
+	int ret;
+
+	ret = pci_enable_device(dev);
+	if (ret)
+		goto out;
+
+	ret = pci_request_regions(dev, "pcips2");
+	if (ret)
+		goto disable;
+
+	ps2if = kzalloc_obj(*ps2if);
+	serio = kzalloc_obj(*serio);
+	if (!ps2if || !serio) {
+		ret = -ENOMEM;
+		goto release;
+	}
+
+
+	serio->id.type		= SERIO_8042;
+	serio->write		= pcips2_write;
+	serio->open		= pcips2_open;
+	serio->close		= pcips2_close;
+	strscpy(serio->name, pci_name(dev), sizeof(serio->name));
+	strscpy(serio->phys, dev_name(&dev->dev), sizeof(serio->phys));
+	serio->port_data	= ps2if;
+	serio->dev.parent	= &dev->dev;
+	ps2if->io		= serio;
+	ps2if->dev		= dev;
+	ps2if->base		= pci_resource_start(dev, 0);
+
+	pci_set_drvdata(dev, ps2if);
+
+	serio_register_port(ps2if->io);
+	return 0;
+
+ release:
+	kfree(ps2if);
+	kfree(serio);
+	pci_release_regions(dev);
+ disable:
+	pci_disable_device(dev);
+ out:
+	return ret;
+}
+
+static void pcips2_remove(struct pci_dev *dev)
+{
+	struct pcips2_data *ps2if = pci_get_drvdata(dev);
+
+	serio_unregister_port(ps2if->io);
+	kfree(ps2if);
+	pci_release_regions(dev);
+	pci_disable_device(dev);
+}
+
+static const struct pci_device_id pcips2_ids[] = {
+	{
+		.vendor		= 0x14f2,	/* MOBILITY */
+		.device		= 0x0123,	/* Keyboard */
+		.subvendor	= PCI_ANY_ID,
+		.subdevice	= PCI_ANY_ID,
+		.class		= PCI_CLASS_INPUT_KEYBOARD << 8,
+		.class_mask	= 0xffff00,
+	},
+	{
+		.vendor		= 0x14f2,	/* MOBILITY */
+		.device		= 0x0124,	/* Mouse */
+		.subvendor	= PCI_ANY_ID,
+		.subdevice	= PCI_ANY_ID,
+		.class		= PCI_CLASS_INPUT_MOUSE << 8,
+		.class_mask	= 0xffff00,
+	},
+	{ 0, }
+};
+MODULE_DEVICE_TABLE(pci, pcips2_ids);
+
+static struct pci_driver pcips2_driver = {
+	.name			= "pcips2",
+	.id_table		= pcips2_ids,
+	.probe			= pcips2_probe,
+	.remove			= pcips2_remove,
+};
+
+module_pci_driver(pcips2_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Russell King <rmk@arm.linux.org.uk>");
+MODULE_DESCRIPTION("PCI PS/2 keyboard/mouse driver");