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, 480 insertions, 0 deletions

diff --git a/drivers/input/serio/gscps2.c b/drivers/input/serio/gscps2.c
new file mode 100644
index 000000000..bf9b993f5
--- /dev/null
+++ b/drivers/input/serio/gscps2.c
@@ -0,0 +1,480 @@
+/*
+ * drivers/input/serio/gscps2.c
+ *
+ * Copyright (c) 2004-2006 Helge Deller <deller@gmx.de>
+ * Copyright (c) 2002 Laurent Canet <canetl@esiee.fr>
+ * Copyright (c) 2002 Thibaut Varene <varenet@parisc-linux.org>
+ *
+ * Pieces of code based on linux-2.4's hp_mouse.c & hp_keyb.c
+ *	Copyright (c) 1999 Alex deVries <alex@onefishtwo.ca>
+ *	Copyright (c) 1999-2000 Philipp Rumpf <prumpf@tux.org>
+ *	Copyright (c) 2000 Xavier Debacker <debackex@esiee.fr>
+ *	Copyright (c) 2000-2001 Thomas Marteau <marteaut@esiee.fr>
+ *
+ * HP GSC PS/2 port driver, found in PA/RISC Workstations
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License.  See the file "COPYING" in the main directory of this archive
+ * for more details.
+ *
+ * TODO:
+ * - Dino testing (did HP ever shipped a machine on which this port
+ *                 was usable/enabled ?)
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/serio.h>
+#include <linux/input.h>
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+#include <linux/delay.h>
+#include <linux/ioport.h>
+
+#include <asm/irq.h>
+#include <asm/io.h>
+#include <asm/parisc-device.h>
+
+MODULE_AUTHOR("Laurent Canet <canetl@esiee.fr>, Thibaut Varene <varenet@parisc-linux.org>, Helge Deller <deller@gmx.de>");
+MODULE_DESCRIPTION("HP GSC PS2 port driver");
+MODULE_LICENSE("GPL");
+
+#define PFX "gscps2.c: "
+
+/*
+ * Driver constants
+ */
+
+/* various constants */
+#define ENABLE			1
+#define DISABLE			0
+
+#define GSC_DINO_OFFSET		0x0800	/* offset for DINO controller versus LASI one */
+
+/* PS/2 IO port offsets */
+#define GSC_ID			0x00	/* device ID offset (see: GSC_ID_XXX) */
+#define GSC_RESET		0x00	/* reset port offset */
+#define GSC_RCVDATA		0x04	/* receive port offset */
+#define GSC_XMTDATA		0x04	/* transmit port offset */
+#define GSC_CONTROL		0x08	/* see: Control register bits */
+#define GSC_STATUS		0x0C	/* see: Status register bits */
+
+/* Control register bits */
+#define GSC_CTRL_ENBL		0x01	/* enable interface */
+#define GSC_CTRL_LPBXR		0x02	/* loopback operation */
+#define GSC_CTRL_DIAG		0x20	/* directly control clock/data line */
+#define GSC_CTRL_DATDIR		0x40	/* data line direct control */
+#define GSC_CTRL_CLKDIR		0x80	/* clock line direct control */
+
+/* Status register bits */
+#define GSC_STAT_RBNE		0x01	/* Receive Buffer Not Empty */
+#define GSC_STAT_TBNE		0x02	/* Transmit Buffer Not Empty */
+#define GSC_STAT_TERR		0x04	/* Timeout Error */
+#define GSC_STAT_PERR		0x08	/* Parity Error */
+#define GSC_STAT_CMPINTR	0x10	/* Composite Interrupt = irq on any port */
+#define GSC_STAT_DATSHD		0x40	/* Data Line Shadow */
+#define GSC_STAT_CLKSHD		0x80	/* Clock Line Shadow */
+
+/* IDs returned by GSC_ID port register */
+#define GSC_ID_KEYBOARD		0	/* device ID values */
+#define GSC_ID_MOUSE		1
+
+
+static irqreturn_t gscps2_interrupt(int irq, void *dev);
+
+#define BUFFER_SIZE 0x0f
+
+/* GSC PS/2 port device struct */
+struct gscps2port {
+	struct list_head node;
+	struct parisc_device *padev;
+	struct serio *port;
+	spinlock_t lock;
+	char __iomem *addr;
+	u8 act, append; /* position in buffer[] */
+	struct {
+		u8 data;
+		u8 str;
+	} buffer[BUFFER_SIZE+1];
+	int id;
+};
+
+/*
+ * Various HW level routines
+ */
+
+#define gscps2_readb_input(x)		readb((x)+GSC_RCVDATA)
+#define gscps2_readb_control(x)		readb((x)+GSC_CONTROL)
+#define gscps2_readb_status(x)		readb((x)+GSC_STATUS)
+#define gscps2_writeb_control(x, y)	writeb((x), (y)+GSC_CONTROL)
+
+
+/*
+ * wait_TBE() - wait for Transmit Buffer Empty
+ */
+
+static int wait_TBE(char __iomem *addr)
+{
+	int timeout = 25000; /* device is expected to react within 250 msec */
+	while (gscps2_readb_status(addr) & GSC_STAT_TBNE) {
+		if (!--timeout)
+			return 0;	/* This should not happen */
+		udelay(10);
+	}
+	return 1;
+}
+
+
+/*
+ * gscps2_flush() - flush the receive buffer
+ */
+
+static void gscps2_flush(struct gscps2port *ps2port)
+{
+	while (gscps2_readb_status(ps2port->addr) & GSC_STAT_RBNE)
+		gscps2_readb_input(ps2port->addr);
+	ps2port->act = ps2port->append = 0;
+}
+
+/*
+ * gscps2_writeb_output() - write a byte to the port
+ *
+ * returns 1 on success, 0 on error
+ */
+
+static inline int gscps2_writeb_output(struct gscps2port *ps2port, u8 data)
+{
+	char __iomem *addr = ps2port->addr;
+
+	if (!wait_TBE(addr)) {
+		printk(KERN_DEBUG PFX "timeout - could not write byte %#x\n", data);
+		return 0;
+	}
+
+	while (gscps2_readb_status(addr) & GSC_STAT_RBNE)
+		/* wait */;
+
+	scoped_guard(spinlock_irqsave, &ps2port->lock)
+		writeb(data, addr+GSC_XMTDATA);
+
+	/* this is ugly, but due to timing of the port it seems to be necessary. */
+	mdelay(6);
+
+	/* make sure any received data is returned as fast as possible */
+	/* this is important e.g. when we set the LEDs on the keyboard */
+	gscps2_interrupt(0, NULL);
+
+	return 1;
+}
+
+
+/*
+ * gscps2_enable() - enables or disables the port
+ */
+
+static void gscps2_enable(struct gscps2port *ps2port, int enable)
+{
+	u8 data;
+
+	/* now enable/disable the port */
+	scoped_guard(spinlock_irqsave, &ps2port->lock) {
+		gscps2_flush(ps2port);
+		data = gscps2_readb_control(ps2port->addr);
+		if (enable)
+			data |= GSC_CTRL_ENBL;
+		else
+			data &= ~GSC_CTRL_ENBL;
+		gscps2_writeb_control(data, ps2port->addr);
+	}
+
+	wait_TBE(ps2port->addr);
+	gscps2_flush(ps2port);
+}
+
+/*
+ * gscps2_reset() - resets the PS/2 port
+ */
+
+static void gscps2_reset(struct gscps2port *ps2port)
+{
+	/* reset the interface */
+	guard(spinlock_irqsave)(&ps2port->lock);
+	gscps2_flush(ps2port);
+	writeb(0xff, ps2port->addr + GSC_RESET);
+	gscps2_flush(ps2port);
+}
+
+static LIST_HEAD(ps2port_list);
+
+static void gscps2_read_data(struct gscps2port *ps2port)
+{
+	u8 status;
+
+	do {
+		status = gscps2_readb_status(ps2port->addr);
+		if (!(status & GSC_STAT_RBNE))
+			break;
+
+		ps2port->buffer[ps2port->append].str = status;
+		ps2port->buffer[ps2port->append].data =
+				gscps2_readb_input(ps2port->addr);
+		ps2port->append = (ps2port->append + 1) & BUFFER_SIZE;
+	} while (true);
+}
+
+static bool gscps2_report_data(struct gscps2port *ps2port)
+{
+	unsigned int rxflags;
+	u8 data, status;
+
+	while (ps2port->act != ps2port->append) {
+		/*
+		 * Did new data arrived while we read existing data ?
+		 * If yes, exit now and let the new irq handler start
+		 * over again.
+		 */
+		if (gscps2_readb_status(ps2port->addr) & GSC_STAT_CMPINTR)
+			return true;
+
+		status = ps2port->buffer[ps2port->act].str;
+		data   = ps2port->buffer[ps2port->act].data;
+
+		ps2port->act = (ps2port->act + 1) & BUFFER_SIZE;
+		rxflags = ((status & GSC_STAT_TERR) ? SERIO_TIMEOUT : 0 ) |
+			  ((status & GSC_STAT_PERR) ? SERIO_PARITY  : 0 );
+
+		serio_interrupt(ps2port->port, data, rxflags);
+	}
+
+	return false;
+}
+
+/**
+ * gscps2_interrupt() - Interruption service routine
+ * @irq: interrupt number which triggered (unused)
+ * @dev: device pointer (unused)
+ *
+ * This function reads received PS/2 bytes and processes them on
+ * all interfaces.
+ * The problematic part here is, that the keyboard and mouse PS/2 port
+ * share the same interrupt and it's not possible to send data if any
+ * one of them holds input data. To solve this problem we try to receive
+ * the data as fast as possible and handle the reporting to the upper layer
+ * later.
+ */
+
+static irqreturn_t gscps2_interrupt(int irq, void *dev)
+{
+	struct gscps2port *ps2port;
+
+	list_for_each_entry(ps2port, &ps2port_list, node) {
+		guard(spinlock_irqsave)(&ps2port->lock);
+
+		gscps2_read_data(ps2port);
+	} /* list_for_each_entry */
+
+	/* all data was read from the ports - now report the data to upper layer */
+	list_for_each_entry(ps2port, &ps2port_list, node) {
+		if (gscps2_report_data(ps2port)) {
+			/* More data ready - break early to restart interrupt */
+			break;
+		}
+	}
+
+	return IRQ_HANDLED;
+}
+
+
+/*
+ * gscps2_write() - send a byte out through the aux interface.
+ */
+
+static int gscps2_write(struct serio *port, unsigned char data)
+{
+	struct gscps2port *ps2port = port->port_data;
+
+	if (!gscps2_writeb_output(ps2port, data)) {
+		printk(KERN_DEBUG PFX "sending byte %#x failed.\n", data);
+		return -1;
+	}
+	return 0;
+}
+
+/*
+ * gscps2_open() is called when a port is opened by the higher layer.
+ * It resets and enables the port.
+ */
+
+static int gscps2_open(struct serio *port)
+{
+	struct gscps2port *ps2port = port->port_data;
+
+	gscps2_reset(ps2port);
+
+	/* enable it */
+	gscps2_enable(ps2port, ENABLE);
+
+	gscps2_interrupt(0, NULL);
+
+	return 0;
+}
+
+/*
+ * gscps2_close() disables the port
+ */
+
+static void gscps2_close(struct serio *port)
+{
+	struct gscps2port *ps2port = port->port_data;
+	gscps2_enable(ps2port, DISABLE);
+}
+
+/**
+ * gscps2_probe() - Probes PS2 devices
+ * @dev: pointer to parisc_device struct which will be probed
+ *
+ * @return: success/error report
+ */
+
+static int __init gscps2_probe(struct parisc_device *dev)
+{
+	struct gscps2port *ps2port;
+	struct serio *serio;
+	unsigned long hpa = dev->hpa.start;
+	int ret;
+
+	if (!dev->irq)
+		return -ENODEV;
+
+	/* Offset for DINO PS/2. Works with LASI even */
+	if (dev->id.sversion == 0x96)
+		hpa += GSC_DINO_OFFSET;
+
+	ps2port = kzalloc_obj(*ps2port);
+	serio = kzalloc_obj(*serio);
+	if (!ps2port || !serio) {
+		ret = -ENOMEM;
+		goto fail_nomem;
+	}
+
+	dev_set_drvdata(&dev->dev, ps2port);
+
+	ps2port->port = serio;
+	ps2port->padev = dev;
+	ps2port->addr = ioremap(hpa, GSC_STATUS + 4);
+	if (!ps2port->addr) {
+		ret = -ENOMEM;
+		goto fail_nomem;
+	}
+	spin_lock_init(&ps2port->lock);
+
+	gscps2_reset(ps2port);
+	ps2port->id = readb(ps2port->addr + GSC_ID) & 0x0f;
+
+	snprintf(serio->name, sizeof(serio->name), "gsc-ps2-%s",
+		 (ps2port->id == GSC_ID_KEYBOARD) ? "keyboard" : "mouse");
+	strscpy(serio->phys, dev_name(&dev->dev), sizeof(serio->phys));
+	serio->id.type		= SERIO_8042;
+	serio->write		= gscps2_write;
+	serio->open		= gscps2_open;
+	serio->close		= gscps2_close;
+	serio->port_data	= ps2port;
+	serio->dev.parent	= &dev->dev;
+
+	ret = -EBUSY;
+	if (request_irq(dev->irq, gscps2_interrupt, IRQF_SHARED, ps2port->port->name, ps2port))
+		goto fail_miserably;
+
+	if (ps2port->id != GSC_ID_KEYBOARD && ps2port->id != GSC_ID_MOUSE) {
+		printk(KERN_WARNING PFX "Unsupported PS/2 port at 0x%08lx (id=%d) ignored\n",
+				hpa, ps2port->id);
+		ret = -ENODEV;
+		goto fail;
+	}
+
+#if 0
+	if (!request_mem_region(hpa, GSC_STATUS + 4, ps2port->port.name))
+		goto fail;
+#endif
+
+	pr_info("serio: %s port at 0x%08lx irq %d @ %s\n",
+		ps2port->port->name,
+		hpa,
+		ps2port->padev->irq,
+		ps2port->port->phys);
+
+	serio_register_port(ps2port->port);
+
+	list_add_tail(&ps2port->node, &ps2port_list);
+
+	return 0;
+
+fail:
+	free_irq(dev->irq, ps2port);
+
+fail_miserably:
+	iounmap(ps2port->addr);
+	release_mem_region(dev->hpa.start, GSC_STATUS + 4);
+
+fail_nomem:
+	kfree(ps2port);
+	kfree(serio);
+	return ret;
+}
+
+/**
+ * gscps2_remove() - Removes PS2 devices
+ * @dev: pointer to parisc_device which shall be removed
+ *
+ * @return: success/error report
+ */
+
+static void __exit gscps2_remove(struct parisc_device *dev)
+{
+	struct gscps2port *ps2port = dev_get_drvdata(&dev->dev);
+
+	serio_unregister_port(ps2port->port);
+	free_irq(dev->irq, ps2port);
+	gscps2_flush(ps2port);
+	list_del(&ps2port->node);
+	iounmap(ps2port->addr);
+#if 0
+	release_mem_region(dev->hpa, GSC_STATUS + 4);
+#endif
+	dev_set_drvdata(&dev->dev, NULL);
+	kfree(ps2port);
+}
+
+
+static const struct parisc_device_id gscps2_device_tbl[] __initconst = {
+	{ HPHW_FIO, HVERSION_REV_ANY_ID, HVERSION_ANY_ID, 0x00084 }, /* LASI PS/2 */
+#ifdef DINO_TESTED
+	{ HPHW_FIO, HVERSION_REV_ANY_ID, HVERSION_ANY_ID, 0x00096 }, /* DINO PS/2 */
+#endif
+	{ 0, }	/* 0 terminated list */
+};
+MODULE_DEVICE_TABLE(parisc, gscps2_device_tbl);
+
+static struct parisc_driver parisc_ps2_driver __refdata = {
+	.name		= "gsc_ps2",
+	.id_table	= gscps2_device_tbl,
+	.probe		= gscps2_probe,
+	.remove		= __exit_p(gscps2_remove),
+};
+
+static int __init gscps2_init(void)
+{
+	register_parisc_driver(&parisc_ps2_driver);
+	return 0;
+}
+
+static void __exit gscps2_exit(void)
+{
+	unregister_parisc_driver(&parisc_ps2_driver);
+}
+
+
+module_init(gscps2_init);
+module_exit(gscps2_exit);
+