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, 204 insertions, 0 deletions

diff --git a/drivers/input/serio/maceps2.c b/drivers/input/serio/maceps2.c
new file mode 100644
index 000000000..fb41e7f5a
--- /dev/null
+++ b/drivers/input/serio/maceps2.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * SGI O2 MACE PS2 controller driver for linux
+ *
+ * Copyright (C) 2002 Vivien Chappelier
+ */
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/serio.h>
+#include <linux/errno.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/err.h>
+
+#include <asm/io.h>
+#include <asm/irq.h>
+#include <asm/ip32/mace.h>
+#include <asm/ip32/ip32_ints.h>
+
+MODULE_AUTHOR("Vivien Chappelier <vivien.chappelier@linux-mips.org");
+MODULE_DESCRIPTION("SGI O2 MACE PS2 controller driver");
+MODULE_LICENSE("GPL");
+
+#define MACE_PS2_TIMEOUT 10000 /* in 50us unit */
+
+#define PS2_STATUS_CLOCK_SIGNAL  BIT(0) /* external clock signal */
+#define PS2_STATUS_CLOCK_INHIBIT BIT(1) /* clken output signal */
+#define PS2_STATUS_TX_INPROGRESS BIT(2) /* transmission in progress */
+#define PS2_STATUS_TX_EMPTY      BIT(3) /* empty transmit buffer */
+#define PS2_STATUS_RX_FULL       BIT(4) /* full receive buffer */
+#define PS2_STATUS_RX_INPROGRESS BIT(5) /* reception in progress */
+#define PS2_STATUS_ERROR_PARITY  BIT(6) /* parity error */
+#define PS2_STATUS_ERROR_FRAMING BIT(7) /* framing error */
+
+#define PS2_CONTROL_TX_CLOCK_DISABLE BIT(0) /* inhibit clock signal after TX */
+#define PS2_CONTROL_TX_ENABLE        BIT(1) /* transmit enable */
+#define PS2_CONTROL_TX_INT_ENABLE    BIT(2) /* enable transmit interrupt */
+#define PS2_CONTROL_RX_INT_ENABLE    BIT(3) /* enable receive interrupt */
+#define PS2_CONTROL_RX_CLOCK_ENABLE  BIT(4) /* pause reception if set to 0 */
+#define PS2_CONTROL_RESET            BIT(5) /* reset */
+
+struct maceps2_data {
+	struct mace_ps2port *port;
+	int irq;
+};
+
+static struct maceps2_data port_data[2];
+static struct serio *maceps2_port[2];
+static struct platform_device *maceps2_device;
+
+static int maceps2_write(struct serio *dev, unsigned char val)
+{
+	struct mace_ps2port *port = ((struct maceps2_data *)dev->port_data)->port;
+	unsigned int timeout = MACE_PS2_TIMEOUT;
+
+	do {
+		if (port->status & PS2_STATUS_TX_EMPTY) {
+			port->tx = val;
+			return 0;
+		}
+		udelay(50);
+	} while (timeout--);
+
+	return -1;
+}
+
+static irqreturn_t maceps2_interrupt(int irq, void *dev_id)
+{
+	struct serio *dev = dev_id;
+	struct mace_ps2port *port = ((struct maceps2_data *)dev->port_data)->port;
+	unsigned long byte;
+
+	if (port->status & PS2_STATUS_RX_FULL) {
+		byte = port->rx;
+		serio_interrupt(dev, byte & 0xff, 0);
+        }
+
+	return IRQ_HANDLED;
+}
+
+static int maceps2_open(struct serio *dev)
+{
+	struct maceps2_data *data = (struct maceps2_data *)dev->port_data;
+
+	if (request_irq(data->irq, maceps2_interrupt, 0, "PS2 port", dev)) {
+		printk(KERN_ERR "Could not allocate PS/2 IRQ\n");
+		return -EBUSY;
+	}
+
+	/* Reset port */
+	data->port->control = PS2_CONTROL_TX_CLOCK_DISABLE | PS2_CONTROL_RESET;
+	udelay(100);
+
+        /* Enable interrupts */
+	data->port->control = PS2_CONTROL_RX_CLOCK_ENABLE |
+			      PS2_CONTROL_TX_ENABLE |
+			      PS2_CONTROL_RX_INT_ENABLE;
+
+	return 0;
+}
+
+static void maceps2_close(struct serio *dev)
+{
+	struct maceps2_data *data = (struct maceps2_data *)dev->port_data;
+
+	data->port->control = PS2_CONTROL_TX_CLOCK_DISABLE | PS2_CONTROL_RESET;
+	udelay(100);
+	free_irq(data->irq, dev);
+}
+
+
+static struct serio *maceps2_allocate_port(int idx)
+{
+	struct serio *serio;
+
+	serio = kzalloc_obj(*serio);
+	if (serio) {
+		serio->id.type		= SERIO_8042;
+		serio->write		= maceps2_write;
+		serio->open		= maceps2_open;
+		serio->close		= maceps2_close;
+		snprintf(serio->name, sizeof(serio->name), "MACE PS/2 port%d", idx);
+		snprintf(serio->phys, sizeof(serio->phys), "mace/serio%d", idx);
+		serio->port_data	= &port_data[idx];
+		serio->dev.parent	= &maceps2_device->dev;
+	}
+
+	return serio;
+}
+
+static int maceps2_probe(struct platform_device *dev)
+{
+	maceps2_port[0] = maceps2_allocate_port(0);
+	maceps2_port[1] = maceps2_allocate_port(1);
+	if (!maceps2_port[0] || !maceps2_port[1]) {
+		kfree(maceps2_port[0]);
+		kfree(maceps2_port[1]);
+		return -ENOMEM;
+	}
+
+	serio_register_port(maceps2_port[0]);
+	serio_register_port(maceps2_port[1]);
+
+	return 0;
+}
+
+static void maceps2_remove(struct platform_device *dev)
+{
+	serio_unregister_port(maceps2_port[0]);
+	serio_unregister_port(maceps2_port[1]);
+}
+
+static struct platform_driver maceps2_driver = {
+	.driver		= {
+		.name	= "maceps2",
+	},
+	.probe		= maceps2_probe,
+	.remove		= maceps2_remove,
+};
+
+static int __init maceps2_init(void)
+{
+	int error;
+
+	error = platform_driver_register(&maceps2_driver);
+	if (error)
+		return error;
+
+	maceps2_device = platform_device_alloc("maceps2", -1);
+	if (!maceps2_device) {
+		error = -ENOMEM;
+		goto err_unregister_driver;
+	}
+
+	port_data[0].port = &mace->perif.ps2.keyb;
+	port_data[0].irq  = MACEISA_KEYB_IRQ;
+	port_data[1].port = &mace->perif.ps2.mouse;
+	port_data[1].irq  = MACEISA_MOUSE_IRQ;
+
+	error = platform_device_add(maceps2_device);
+	if (error)
+		goto err_free_device;
+
+	return 0;
+
+ err_free_device:
+	platform_device_put(maceps2_device);
+ err_unregister_driver:
+	platform_driver_unregister(&maceps2_driver);
+	return error;
+}
+
+static void __exit maceps2_exit(void)
+{
+	platform_device_unregister(maceps2_device);
+	platform_driver_unregister(&maceps2_driver);
+}
+
+module_init(maceps2_init);
+module_exit(maceps2_exit);