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, 209 insertions, 0 deletions

diff --git a/drivers/input/serio/ambakmi.c b/drivers/input/serio/ambakmi.c
new file mode 100644
index 000000000..046b8f388
--- /dev/null
+++ b/drivers/input/serio/ambakmi.c
@@ -0,0 +1,209 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  linux/drivers/input/serio/ambakmi.c
+ *
+ *  Copyright (C) 2000-2003 Deep Blue Solutions Ltd.
+ *  Copyright (C) 2002 Russell King.
+ */
+#include <linux/module.h>
+#include <linux/serio.h>
+#include <linux/errno.h>
+#include <linux/interrupt.h>
+#include <linux/ioport.h>
+#include <linux/device.h>
+#include <linux/delay.h>
+#include <linux/slab.h>
+#include <linux/err.h>
+#include <linux/amba/bus.h>
+#include <linux/amba/kmi.h>
+#include <linux/clk.h>
+
+#include <asm/io.h>
+#include <asm/irq.h>
+
+#define KMI_BASE	(kmi->base)
+
+struct amba_kmi_port {
+	struct serio		*io;
+	struct clk		*clk;
+	void __iomem		*base;
+	unsigned int		irq;
+	unsigned int		divisor;
+	unsigned int		open;
+};
+
+static irqreturn_t amba_kmi_int(int irq, void *dev_id)
+{
+	struct amba_kmi_port *kmi = dev_id;
+	unsigned int status = readb(KMIIR);
+	int handled = IRQ_NONE;
+
+	while (status & KMIIR_RXINTR) {
+		serio_interrupt(kmi->io, readb(KMIDATA), 0);
+		status = readb(KMIIR);
+		handled = IRQ_HANDLED;
+	}
+
+	return handled;
+}
+
+static int amba_kmi_write(struct serio *io, unsigned char val)
+{
+	struct amba_kmi_port *kmi = io->port_data;
+	unsigned int timeleft = 10000; /* timeout in 100ms */
+
+	while ((readb(KMISTAT) & KMISTAT_TXEMPTY) == 0 && --timeleft)
+		udelay(10);
+
+	if (timeleft)
+		writeb(val, KMIDATA);
+
+	return timeleft ? 0 : SERIO_TIMEOUT;
+}
+
+static int amba_kmi_open(struct serio *io)
+{
+	struct amba_kmi_port *kmi = io->port_data;
+	unsigned int divisor;
+	int ret;
+
+	ret = clk_prepare_enable(kmi->clk);
+	if (ret)
+		goto out;
+
+	divisor = clk_get_rate(kmi->clk) / 8000000 - 1;
+	writeb(divisor, KMICLKDIV);
+	writeb(KMICR_EN, KMICR);
+
+	ret = request_irq(kmi->irq, amba_kmi_int, IRQF_SHARED, "kmi-pl050",
+			  kmi);
+	if (ret) {
+		printk(KERN_ERR "kmi: failed to claim IRQ%d\n", kmi->irq);
+		writeb(0, KMICR);
+		goto clk_disable;
+	}
+
+	writeb(KMICR_EN | KMICR_RXINTREN, KMICR);
+
+	return 0;
+
+ clk_disable:
+	clk_disable_unprepare(kmi->clk);
+ out:
+	return ret;
+}
+
+static void amba_kmi_close(struct serio *io)
+{
+	struct amba_kmi_port *kmi = io->port_data;
+
+	writeb(0, KMICR);
+
+	free_irq(kmi->irq, kmi);
+	clk_disable_unprepare(kmi->clk);
+}
+
+static int amba_kmi_probe(struct amba_device *dev,
+	const struct amba_id *id)
+{
+	struct amba_kmi_port *kmi;
+	struct serio *io;
+	int ret;
+
+	ret = amba_request_regions(dev, NULL);
+	if (ret)
+		return ret;
+
+	kmi = kzalloc_obj(*kmi);
+	io = kzalloc_obj(*io);
+	if (!kmi || !io) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+
+	io->id.type	= SERIO_8042;
+	io->write	= amba_kmi_write;
+	io->open	= amba_kmi_open;
+	io->close	= amba_kmi_close;
+	strscpy(io->name, dev_name(&dev->dev), sizeof(io->name));
+	strscpy(io->phys, dev_name(&dev->dev), sizeof(io->phys));
+	io->port_data	= kmi;
+	io->dev.parent	= &dev->dev;
+
+	kmi->io		= io;
+	kmi->base	= ioremap(dev->res.start, resource_size(&dev->res));
+	if (!kmi->base) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	kmi->clk = clk_get(&dev->dev, "KMIREFCLK");
+	if (IS_ERR(kmi->clk)) {
+		ret = PTR_ERR(kmi->clk);
+		goto unmap;
+	}
+
+	kmi->irq = dev->irq[0];
+	amba_set_drvdata(dev, kmi);
+
+	serio_register_port(kmi->io);
+	return 0;
+
+ unmap:
+	iounmap(kmi->base);
+ out:
+	kfree(kmi);
+	kfree(io);
+	amba_release_regions(dev);
+	return ret;
+}
+
+static void amba_kmi_remove(struct amba_device *dev)
+{
+	struct amba_kmi_port *kmi = amba_get_drvdata(dev);
+
+	serio_unregister_port(kmi->io);
+	clk_put(kmi->clk);
+	iounmap(kmi->base);
+	kfree(kmi);
+	amba_release_regions(dev);
+}
+
+static int amba_kmi_resume(struct device *dev)
+{
+	struct amba_kmi_port *kmi = dev_get_drvdata(dev);
+
+	/* kick the serio layer to rescan this port */
+	serio_reconnect(kmi->io);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(amba_kmi_dev_pm_ops, NULL, amba_kmi_resume);
+
+static const struct amba_id amba_kmi_idtable[] = {
+	{
+		.id	= 0x00041050,
+		.mask	= 0x000fffff,
+	},
+	{ 0, 0 }
+};
+
+MODULE_DEVICE_TABLE(amba, amba_kmi_idtable);
+
+static struct amba_driver ambakmi_driver = {
+	.drv		= {
+		.name	= "kmi-pl050",
+		.pm	= pm_sleep_ptr(&amba_kmi_dev_pm_ops),
+	},
+	.id_table	= amba_kmi_idtable,
+	.probe		= amba_kmi_probe,
+	.remove		= amba_kmi_remove,
+};
+
+module_amba_driver(ambakmi_driver);
+
+MODULE_AUTHOR("Russell King <rmk@arm.linux.org.uk>");
+MODULE_DESCRIPTION("AMBA KMI controller driver");
+MODULE_LICENSE("GPL");