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, 266 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-vt8500.c b/drivers/rtc/rtc-vt8500.c
new file mode 100644
index 000000000..c8b568498
--- /dev/null
+++ b/drivers/rtc/rtc-vt8500.c
@@ -0,0 +1,266 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * drivers/rtc/rtc-vt8500.c
+ *
+ *  Copyright (C) 2010 Alexey Charkov <alchark@gmail.com>
+ *
+ * Based on rtc-pxa.c
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/bcd.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+
+/*
+ * Register definitions
+ */
+#define VT8500_RTC_TS		0x00	/* Time set */
+#define VT8500_RTC_DS		0x04	/* Date set */
+#define VT8500_RTC_AS		0x08	/* Alarm set */
+#define VT8500_RTC_CR		0x0c	/* Control */
+#define VT8500_RTC_TR		0x10	/* Time read */
+#define VT8500_RTC_DR		0x14	/* Date read */
+#define VT8500_RTC_WS		0x18	/* Write status */
+#define VT8500_RTC_CL		0x20	/* Calibration */
+#define VT8500_RTC_IS		0x24	/* Interrupt status */
+#define VT8500_RTC_ST		0x28	/* Status */
+
+#define INVALID_TIME_BIT	(1 << 31)
+
+#define DATE_CENTURY_S		19
+#define DATE_YEAR_S		11
+#define DATE_YEAR_MASK		(0xff << DATE_YEAR_S)
+#define DATE_MONTH_S		6
+#define DATE_MONTH_MASK		(0x1f << DATE_MONTH_S)
+#define DATE_DAY_MASK		0x3f
+
+#define TIME_DOW_S		20
+#define TIME_DOW_MASK		(0x07 << TIME_DOW_S)
+#define TIME_HOUR_S		14
+#define TIME_HOUR_MASK		(0x3f << TIME_HOUR_S)
+#define TIME_MIN_S		7
+#define TIME_MIN_MASK		(0x7f << TIME_MIN_S)
+#define TIME_SEC_MASK		0x7f
+
+#define ALARM_DAY_S		20
+#define ALARM_DAY_MASK		(0x3f << ALARM_DAY_S)
+
+#define ALARM_DAY_BIT		(1 << 29)
+#define ALARM_HOUR_BIT		(1 << 28)
+#define ALARM_MIN_BIT		(1 << 27)
+#define ALARM_SEC_BIT		(1 << 26)
+
+#define ALARM_ENABLE_MASK	(ALARM_DAY_BIT \
+				| ALARM_HOUR_BIT \
+				| ALARM_MIN_BIT \
+				| ALARM_SEC_BIT)
+
+#define VT8500_RTC_CR_ENABLE	(1 << 0)	/* Enable RTC */
+#define VT8500_RTC_CR_12H	(1 << 1)	/* 12h time format */
+#define VT8500_RTC_CR_SM_ENABLE	(1 << 2)	/* Enable periodic irqs */
+#define VT8500_RTC_CR_SM_SEC	(1 << 3)	/* 0: 1Hz/60, 1: 1Hz */
+#define VT8500_RTC_CR_CALIB	(1 << 4)	/* Enable calibration */
+
+#define VT8500_RTC_IS_ALARM	(1 << 0)	/* Alarm interrupt status */
+
+struct vt8500_rtc {
+	void __iomem		*regbase;
+	int			irq_alarm;
+	struct rtc_device	*rtc;
+	spinlock_t		lock;		/* Protects this structure */
+};
+
+static irqreturn_t vt8500_rtc_irq(int irq, void *dev_id)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_id;
+	u32 isr;
+	unsigned long events = 0;
+
+	spin_lock(&vt8500_rtc->lock);
+
+	/* clear interrupt sources */
+	isr = readl(vt8500_rtc->regbase + VT8500_RTC_IS);
+	writel(isr, vt8500_rtc->regbase + VT8500_RTC_IS);
+
+	spin_unlock(&vt8500_rtc->lock);
+
+	if (isr & VT8500_RTC_IS_ALARM)
+		events |= RTC_AF | RTC_IRQF;
+
+	rtc_update_irq(vt8500_rtc->rtc, 1, events);
+
+	return IRQ_HANDLED;
+}
+
+static int vt8500_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_get_drvdata(dev);
+	u32 date, time;
+
+	date = readl(vt8500_rtc->regbase + VT8500_RTC_DR);
+	time = readl(vt8500_rtc->regbase + VT8500_RTC_TR);
+
+	tm->tm_sec = bcd2bin(time & TIME_SEC_MASK);
+	tm->tm_min = bcd2bin((time & TIME_MIN_MASK) >> TIME_MIN_S);
+	tm->tm_hour = bcd2bin((time & TIME_HOUR_MASK) >> TIME_HOUR_S);
+	tm->tm_mday = bcd2bin(date & DATE_DAY_MASK);
+	tm->tm_mon = bcd2bin((date & DATE_MONTH_MASK) >> DATE_MONTH_S) - 1;
+	tm->tm_year = bcd2bin((date & DATE_YEAR_MASK) >> DATE_YEAR_S)
+			+ ((date >> DATE_CENTURY_S) & 1 ? 200 : 100);
+	tm->tm_wday = (time & TIME_DOW_MASK) >> TIME_DOW_S;
+
+	return 0;
+}
+
+static int vt8500_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_get_drvdata(dev);
+
+	writel((bin2bcd(tm->tm_year % 100) << DATE_YEAR_S)
+		| (bin2bcd(tm->tm_mon + 1) << DATE_MONTH_S)
+		| (bin2bcd(tm->tm_mday))
+		| ((tm->tm_year >= 200) << DATE_CENTURY_S),
+		vt8500_rtc->regbase + VT8500_RTC_DS);
+	writel((bin2bcd(tm->tm_wday) << TIME_DOW_S)
+		| (bin2bcd(tm->tm_hour) << TIME_HOUR_S)
+		| (bin2bcd(tm->tm_min) << TIME_MIN_S)
+		| (bin2bcd(tm->tm_sec)),
+		vt8500_rtc->regbase + VT8500_RTC_TS);
+
+	return 0;
+}
+
+static int vt8500_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_get_drvdata(dev);
+	u32 isr, alarm;
+
+	alarm = readl(vt8500_rtc->regbase + VT8500_RTC_AS);
+	isr = readl(vt8500_rtc->regbase + VT8500_RTC_IS);
+
+	alrm->time.tm_mday = bcd2bin((alarm & ALARM_DAY_MASK) >> ALARM_DAY_S);
+	alrm->time.tm_hour = bcd2bin((alarm & TIME_HOUR_MASK) >> TIME_HOUR_S);
+	alrm->time.tm_min = bcd2bin((alarm & TIME_MIN_MASK) >> TIME_MIN_S);
+	alrm->time.tm_sec = bcd2bin((alarm & TIME_SEC_MASK));
+
+	alrm->enabled = (alarm & ALARM_ENABLE_MASK) ? 1 : 0;
+	alrm->pending = (isr & VT8500_RTC_IS_ALARM) ? 1 : 0;
+
+	return rtc_valid_tm(&alrm->time);
+}
+
+static int vt8500_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_get_drvdata(dev);
+
+	writel((alrm->enabled ? ALARM_ENABLE_MASK : 0)
+		| (bin2bcd(alrm->time.tm_mday) << ALARM_DAY_S)
+		| (bin2bcd(alrm->time.tm_hour) << TIME_HOUR_S)
+		| (bin2bcd(alrm->time.tm_min) << TIME_MIN_S)
+		| (bin2bcd(alrm->time.tm_sec)),
+		vt8500_rtc->regbase + VT8500_RTC_AS);
+
+	return 0;
+}
+
+static int vt8500_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct vt8500_rtc *vt8500_rtc = dev_get_drvdata(dev);
+	unsigned long tmp = readl(vt8500_rtc->regbase + VT8500_RTC_AS);
+
+	if (enabled)
+		tmp |= ALARM_ENABLE_MASK;
+	else
+		tmp &= ~ALARM_ENABLE_MASK;
+
+	writel(tmp, vt8500_rtc->regbase + VT8500_RTC_AS);
+	return 0;
+}
+
+static const struct rtc_class_ops vt8500_rtc_ops = {
+	.read_time = vt8500_rtc_read_time,
+	.set_time = vt8500_rtc_set_time,
+	.read_alarm = vt8500_rtc_read_alarm,
+	.set_alarm = vt8500_rtc_set_alarm,
+	.alarm_irq_enable = vt8500_alarm_irq_enable,
+};
+
+static int vt8500_rtc_probe(struct platform_device *pdev)
+{
+	struct vt8500_rtc *vt8500_rtc;
+	int ret;
+
+	vt8500_rtc = devm_kzalloc(&pdev->dev,
+			   sizeof(struct vt8500_rtc), GFP_KERNEL);
+	if (!vt8500_rtc)
+		return -ENOMEM;
+
+	spin_lock_init(&vt8500_rtc->lock);
+	platform_set_drvdata(pdev, vt8500_rtc);
+
+	vt8500_rtc->irq_alarm = platform_get_irq(pdev, 0);
+	if (vt8500_rtc->irq_alarm < 0)
+		return vt8500_rtc->irq_alarm;
+
+	vt8500_rtc->regbase = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(vt8500_rtc->regbase))
+		return PTR_ERR(vt8500_rtc->regbase);
+
+	/* Enable RTC and set it to 24-hour mode */
+	writel(VT8500_RTC_CR_ENABLE,
+	       vt8500_rtc->regbase + VT8500_RTC_CR);
+
+	vt8500_rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(vt8500_rtc->rtc))
+		return PTR_ERR(vt8500_rtc->rtc);
+
+	vt8500_rtc->rtc->ops = &vt8500_rtc_ops;
+	vt8500_rtc->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	vt8500_rtc->rtc->range_max = RTC_TIMESTAMP_END_2199;
+
+	ret = devm_request_irq(&pdev->dev, vt8500_rtc->irq_alarm,
+				vt8500_rtc_irq, 0, "rtc alarm", vt8500_rtc);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "can't get irq %i, err %d\n",
+			vt8500_rtc->irq_alarm, ret);
+		return ret;
+	}
+
+	return devm_rtc_register_device(vt8500_rtc->rtc);
+}
+
+static void vt8500_rtc_remove(struct platform_device *pdev)
+{
+	struct vt8500_rtc *vt8500_rtc = platform_get_drvdata(pdev);
+
+	/* Disable alarm matching */
+	writel(0, vt8500_rtc->regbase + VT8500_RTC_IS);
+}
+
+static const struct of_device_id wmt_dt_ids[] = {
+	{ .compatible = "via,vt8500-rtc", },
+	{}
+};
+MODULE_DEVICE_TABLE(of, wmt_dt_ids);
+
+static struct platform_driver vt8500_rtc_driver = {
+	.probe		= vt8500_rtc_probe,
+	.remove		= vt8500_rtc_remove,
+	.driver		= {
+		.name	= "vt8500-rtc",
+		.of_match_table = wmt_dt_ids,
+	},
+};
+
+module_platform_driver(vt8500_rtc_driver);
+
+MODULE_AUTHOR("Alexey Charkov <alchark@gmail.com>");
+MODULE_DESCRIPTION("VIA VT8500 SoC Realtime Clock Driver (RTC)");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:vt8500-rtc");