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, 221 insertions, 0 deletions

diff --git a/drivers/input/serio/ioc3kbd.c b/drivers/input/serio/ioc3kbd.c
new file mode 100644
index 000000000..4ef60c24e
--- /dev/null
+++ b/drivers/input/serio/ioc3kbd.c
@@ -0,0 +1,221 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * SGI IOC3 PS/2 controller driver for linux
+ *
+ * Copyright (C) 2019 Thomas Bogendoerfer <tbogendoerfer@suse.de>
+ *
+ * Based on code Copyright (C) 2005 Stanislaw Skowronek <skylark@unaligned.org>
+ *               Copyright (C) 2009 Johannes Dickgreber <tanzy@gmx.de>
+ */
+
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/serio.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+#include <asm/sn/ioc3.h>
+
+struct ioc3kbd_data {
+	struct ioc3_serioregs __iomem *regs;
+	struct serio *kbd, *aux;
+	bool kbd_exists, aux_exists;
+	int irq;
+};
+
+static int ioc3kbd_wait(struct ioc3_serioregs __iomem *regs, u32 mask)
+{
+	unsigned long timeout = 0;
+
+	while ((readl(&regs->km_csr) & mask) && (timeout < 250)) {
+		udelay(50);
+		timeout++;
+	}
+	return (timeout >= 250) ? -ETIMEDOUT : 0;
+}
+
+static int ioc3kbd_write(struct serio *dev, u8 val)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+	int ret;
+
+	ret = ioc3kbd_wait(d->regs, KM_CSR_K_WRT_PEND);
+	if (ret)
+		return ret;
+
+	writel(val, &d->regs->k_wd);
+
+	return 0;
+}
+
+static int ioc3kbd_start(struct serio *dev)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+
+	d->kbd_exists = true;
+	return 0;
+}
+
+static void ioc3kbd_stop(struct serio *dev)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+
+	d->kbd_exists = false;
+}
+
+static int ioc3aux_write(struct serio *dev, u8 val)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+	int ret;
+
+	ret = ioc3kbd_wait(d->regs, KM_CSR_M_WRT_PEND);
+	if (ret)
+		return ret;
+
+	writel(val, &d->regs->m_wd);
+
+	return 0;
+}
+
+static int ioc3aux_start(struct serio *dev)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+
+	d->aux_exists = true;
+	return 0;
+}
+
+static void ioc3aux_stop(struct serio *dev)
+{
+	struct ioc3kbd_data *d = dev->port_data;
+
+	d->aux_exists = false;
+}
+
+static void ioc3kbd_process_data(struct serio *dev, u32 data)
+{
+	if (data & KM_RD_VALID_0)
+		serio_interrupt(dev, (data >> KM_RD_DATA_0_SHIFT) & 0xff, 0);
+	if (data & KM_RD_VALID_1)
+		serio_interrupt(dev, (data >> KM_RD_DATA_1_SHIFT) & 0xff, 0);
+	if (data & KM_RD_VALID_2)
+		serio_interrupt(dev, (data >> KM_RD_DATA_2_SHIFT) & 0xff, 0);
+}
+
+static irqreturn_t ioc3kbd_intr(int itq, void *dev_id)
+{
+	struct ioc3kbd_data *d = dev_id;
+	u32 data_k, data_m;
+
+	data_k = readl(&d->regs->k_rd);
+	if (d->kbd_exists)
+		ioc3kbd_process_data(d->kbd, data_k);
+
+	data_m = readl(&d->regs->m_rd);
+	if (d->aux_exists)
+		ioc3kbd_process_data(d->aux, data_m);
+
+	return IRQ_HANDLED;
+}
+
+static int ioc3kbd_probe(struct platform_device *pdev)
+{
+	struct ioc3_serioregs __iomem *regs;
+	struct device *dev = &pdev->dev;
+	struct ioc3kbd_data *d;
+	struct serio *sk, *sa;
+	int irq, ret;
+
+	regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(regs))
+		return PTR_ERR(regs);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return -ENXIO;
+
+	d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);
+	if (!d)
+		return -ENOMEM;
+
+	sk = kzalloc_obj(*sk);
+	if (!sk)
+		return -ENOMEM;
+
+	sa = kzalloc_obj(*sa);
+	if (!sa) {
+		kfree(sk);
+		return -ENOMEM;
+	}
+
+	sk->id.type = SERIO_8042;
+	sk->write = ioc3kbd_write;
+	sk->start = ioc3kbd_start;
+	sk->stop = ioc3kbd_stop;
+	snprintf(sk->name, sizeof(sk->name), "IOC3 keyboard %d", pdev->id);
+	snprintf(sk->phys, sizeof(sk->phys), "ioc3/serio%dkbd", pdev->id);
+	sk->port_data = d;
+	sk->dev.parent = dev;
+
+	sa->id.type = SERIO_8042;
+	sa->write = ioc3aux_write;
+	sa->start = ioc3aux_start;
+	sa->stop = ioc3aux_stop;
+	snprintf(sa->name, sizeof(sa->name), "IOC3 auxiliary %d", pdev->id);
+	snprintf(sa->phys, sizeof(sa->phys), "ioc3/serio%daux", pdev->id);
+	sa->port_data = d;
+	sa->dev.parent = dev;
+
+	d->regs = regs;
+	d->kbd = sk;
+	d->aux = sa;
+	d->irq = irq;
+
+	platform_set_drvdata(pdev, d);
+	serio_register_port(d->kbd);
+	serio_register_port(d->aux);
+
+	ret = request_irq(irq, ioc3kbd_intr, IRQF_SHARED, "ioc3-kbd", d);
+	if (ret) {
+		dev_err(dev, "could not request IRQ %d\n", irq);
+		serio_unregister_port(d->kbd);
+		serio_unregister_port(d->aux);
+		return ret;
+	}
+
+	/* enable ports */
+	writel(KM_CSR_K_CLAMP_3 | KM_CSR_M_CLAMP_3, &regs->km_csr);
+
+	return 0;
+}
+
+static void ioc3kbd_remove(struct platform_device *pdev)
+{
+	struct ioc3kbd_data *d = platform_get_drvdata(pdev);
+
+	free_irq(d->irq, d);
+
+	serio_unregister_port(d->kbd);
+	serio_unregister_port(d->aux);
+}
+
+static const struct platform_device_id ioc3kbd_id_table[] = {
+	{ "ioc3-kbd", },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, ioc3kbd_id_table);
+
+static struct platform_driver ioc3kbd_driver = {
+	.probe          = ioc3kbd_probe,
+	.remove         = ioc3kbd_remove,
+	.id_table	= ioc3kbd_id_table,
+	.driver = {
+		.name = "ioc3-kbd",
+	},
+};
+module_platform_driver(ioc3kbd_driver);
+
+MODULE_AUTHOR("Thomas Bogendoerfer <tbogendoerfer@suse.de>");
+MODULE_DESCRIPTION("SGI IOC3 serio driver");
+MODULE_LICENSE("GPL");