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, 360 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-lpc32xx.c b/drivers/rtc/rtc-lpc32xx.c
new file mode 100644
index 000000000..74280bffe
--- /dev/null
+++ b/drivers/rtc/rtc-lpc32xx.c
@@ -0,0 +1,360 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2010 NXP Semiconductors
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/spinlock.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+#include <linux/io.h>
+#include <linux/of.h>
+
+/*
+ * Clock and Power control register offsets
+ */
+#define LPC32XX_RTC_UCOUNT		0x00
+#define LPC32XX_RTC_DCOUNT		0x04
+#define LPC32XX_RTC_MATCH0		0x08
+#define LPC32XX_RTC_MATCH1		0x0C
+#define LPC32XX_RTC_CTRL		0x10
+#define LPC32XX_RTC_INTSTAT		0x14
+#define LPC32XX_RTC_KEY			0x18
+#define LPC32XX_RTC_SRAM		0x80
+
+#define LPC32XX_RTC_CTRL_MATCH0		(1 << 0)
+#define LPC32XX_RTC_CTRL_MATCH1		(1 << 1)
+#define LPC32XX_RTC_CTRL_ONSW_MATCH0	(1 << 2)
+#define LPC32XX_RTC_CTRL_ONSW_MATCH1	(1 << 3)
+#define LPC32XX_RTC_CTRL_SW_RESET	(1 << 4)
+#define LPC32XX_RTC_CTRL_CNTR_DIS	(1 << 6)
+#define LPC32XX_RTC_CTRL_ONSW_FORCE_HI	(1 << 7)
+
+#define LPC32XX_RTC_INTSTAT_MATCH0	(1 << 0)
+#define LPC32XX_RTC_INTSTAT_MATCH1	(1 << 1)
+#define LPC32XX_RTC_INTSTAT_ONSW	(1 << 2)
+
+#define LPC32XX_RTC_KEY_ONSW_LOADVAL	0xB5C13F27
+
+#define rtc_readl(dev, reg) \
+	__raw_readl((dev)->rtc_base + (reg))
+#define rtc_writel(dev, reg, val) \
+	__raw_writel((val), (dev)->rtc_base + (reg))
+
+struct lpc32xx_rtc {
+	void __iomem *rtc_base;
+	int irq;
+	unsigned char alarm_enabled;
+	struct rtc_device *rtc;
+	spinlock_t lock;
+};
+
+static int lpc32xx_rtc_read_time(struct device *dev, struct rtc_time *time)
+{
+	unsigned long elapsed_sec;
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	elapsed_sec = rtc_readl(rtc, LPC32XX_RTC_UCOUNT);
+	rtc_time64_to_tm(elapsed_sec, time);
+
+	return 0;
+}
+
+static int lpc32xx_rtc_set_time(struct device *dev, struct rtc_time *time)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+	u32 secs = rtc_tm_to_time64(time);
+	u32 tmp;
+
+	spin_lock_irq(&rtc->lock);
+
+	/* RTC must be disabled during count update */
+	tmp = rtc_readl(rtc, LPC32XX_RTC_CTRL);
+	rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp | LPC32XX_RTC_CTRL_CNTR_DIS);
+	rtc_writel(rtc, LPC32XX_RTC_UCOUNT, secs);
+	rtc_writel(rtc, LPC32XX_RTC_DCOUNT, 0xFFFFFFFF - secs);
+	rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp &= ~LPC32XX_RTC_CTRL_CNTR_DIS);
+
+	spin_unlock_irq(&rtc->lock);
+
+	return 0;
+}
+
+static int lpc32xx_rtc_read_alarm(struct device *dev,
+	struct rtc_wkalrm *wkalrm)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	rtc_time64_to_tm(rtc_readl(rtc, LPC32XX_RTC_MATCH0), &wkalrm->time);
+	wkalrm->enabled = rtc->alarm_enabled;
+	wkalrm->pending = !!(rtc_readl(rtc, LPC32XX_RTC_INTSTAT) &
+		LPC32XX_RTC_INTSTAT_MATCH0);
+
+	return rtc_valid_tm(&wkalrm->time);
+}
+
+static int lpc32xx_rtc_set_alarm(struct device *dev,
+	struct rtc_wkalrm *wkalrm)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+	unsigned long alarmsecs;
+	u32 tmp;
+
+	alarmsecs = rtc_tm_to_time64(&wkalrm->time);
+
+	spin_lock_irq(&rtc->lock);
+
+	/* Disable alarm during update */
+	tmp = rtc_readl(rtc, LPC32XX_RTC_CTRL);
+	rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp & ~LPC32XX_RTC_CTRL_MATCH0);
+
+	rtc_writel(rtc, LPC32XX_RTC_MATCH0, alarmsecs);
+
+	rtc->alarm_enabled = wkalrm->enabled;
+	if (wkalrm->enabled) {
+		rtc_writel(rtc, LPC32XX_RTC_INTSTAT,
+			   LPC32XX_RTC_INTSTAT_MATCH0);
+		rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp |
+			   LPC32XX_RTC_CTRL_MATCH0);
+	}
+
+	spin_unlock_irq(&rtc->lock);
+
+	return 0;
+}
+
+static int lpc32xx_rtc_alarm_irq_enable(struct device *dev,
+	unsigned int enabled)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+	u32 tmp;
+
+	spin_lock_irq(&rtc->lock);
+	tmp = rtc_readl(rtc, LPC32XX_RTC_CTRL);
+
+	if (enabled) {
+		rtc->alarm_enabled = 1;
+		tmp |= LPC32XX_RTC_CTRL_MATCH0;
+	} else {
+		rtc->alarm_enabled = 0;
+		tmp &= ~LPC32XX_RTC_CTRL_MATCH0;
+	}
+
+	rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp);
+	spin_unlock_irq(&rtc->lock);
+
+	return 0;
+}
+
+static irqreturn_t lpc32xx_rtc_alarm_interrupt(int irq, void *dev)
+{
+	struct lpc32xx_rtc *rtc = dev;
+
+	spin_lock(&rtc->lock);
+
+	/* Disable alarm interrupt */
+	rtc_writel(rtc, LPC32XX_RTC_CTRL,
+		rtc_readl(rtc, LPC32XX_RTC_CTRL) &
+			  ~LPC32XX_RTC_CTRL_MATCH0);
+	rtc->alarm_enabled = 0;
+
+	/*
+	 * Write a large value to the match value so the RTC won't
+	 * keep firing the match status
+	 */
+	rtc_writel(rtc, LPC32XX_RTC_MATCH0, 0xFFFFFFFF);
+	rtc_writel(rtc, LPC32XX_RTC_INTSTAT, LPC32XX_RTC_INTSTAT_MATCH0);
+
+	spin_unlock(&rtc->lock);
+
+	rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops lpc32xx_rtc_ops = {
+	.read_time		= lpc32xx_rtc_read_time,
+	.set_time		= lpc32xx_rtc_set_time,
+	.read_alarm		= lpc32xx_rtc_read_alarm,
+	.set_alarm		= lpc32xx_rtc_set_alarm,
+	.alarm_irq_enable	= lpc32xx_rtc_alarm_irq_enable,
+};
+
+static int lpc32xx_rtc_probe(struct platform_device *pdev)
+{
+	struct lpc32xx_rtc *rtc;
+	int err;
+	u32 tmp;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (unlikely(!rtc))
+		return -ENOMEM;
+
+	rtc->rtc_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rtc->rtc_base))
+		return PTR_ERR(rtc->rtc_base);
+
+	spin_lock_init(&rtc->lock);
+
+	/*
+	 * The RTC is on a separate power domain and can keep it's state
+	 * across a chip power cycle. If the RTC has never been previously
+	 * setup, then set it up now for the first time.
+	 */
+	tmp = rtc_readl(rtc, LPC32XX_RTC_CTRL);
+	if (rtc_readl(rtc, LPC32XX_RTC_KEY) != LPC32XX_RTC_KEY_ONSW_LOADVAL) {
+		tmp &= ~(LPC32XX_RTC_CTRL_SW_RESET |
+			LPC32XX_RTC_CTRL_CNTR_DIS |
+			LPC32XX_RTC_CTRL_MATCH0 |
+			LPC32XX_RTC_CTRL_MATCH1 |
+			LPC32XX_RTC_CTRL_ONSW_MATCH0 |
+			LPC32XX_RTC_CTRL_ONSW_MATCH1 |
+			LPC32XX_RTC_CTRL_ONSW_FORCE_HI);
+		rtc_writel(rtc, LPC32XX_RTC_CTRL, tmp);
+
+		/* Clear latched interrupt states */
+		rtc_writel(rtc, LPC32XX_RTC_MATCH0, 0xFFFFFFFF);
+		rtc_writel(rtc, LPC32XX_RTC_INTSTAT,
+			   LPC32XX_RTC_INTSTAT_MATCH0 |
+			   LPC32XX_RTC_INTSTAT_MATCH1 |
+			   LPC32XX_RTC_INTSTAT_ONSW);
+
+		/* Write key value to RTC so it won't reload on reset */
+		rtc_writel(rtc, LPC32XX_RTC_KEY,
+			   LPC32XX_RTC_KEY_ONSW_LOADVAL);
+	} else {
+		rtc_writel(rtc, LPC32XX_RTC_CTRL,
+			   tmp & ~LPC32XX_RTC_CTRL_MATCH0);
+	}
+
+	platform_set_drvdata(pdev, rtc);
+
+	rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtc))
+		return PTR_ERR(rtc->rtc);
+
+	rtc->rtc->ops = &lpc32xx_rtc_ops;
+	rtc->rtc->range_max = U32_MAX;
+
+	err = devm_rtc_register_device(rtc->rtc);
+	if (err)
+		return err;
+
+	/*
+	 * IRQ is enabled after device registration in case alarm IRQ
+	 * is pending upon suspend exit.
+	 */
+	rtc->irq = platform_get_irq(pdev, 0);
+	if (rtc->irq < 0) {
+		dev_warn(&pdev->dev, "Can't get interrupt resource\n");
+	} else {
+		if (devm_request_irq(&pdev->dev, rtc->irq,
+				     lpc32xx_rtc_alarm_interrupt,
+				     0, pdev->name, rtc) < 0) {
+			dev_warn(&pdev->dev, "Can't request interrupt.\n");
+			rtc->irq = -1;
+		} else {
+			device_init_wakeup(&pdev->dev, true);
+		}
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_PM
+static int lpc32xx_rtc_suspend(struct device *dev)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	if (rtc->irq >= 0) {
+		if (device_may_wakeup(dev))
+			enable_irq_wake(rtc->irq);
+		else
+			disable_irq_wake(rtc->irq);
+	}
+
+	return 0;
+}
+
+static int lpc32xx_rtc_resume(struct device *dev)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	if (rtc->irq >= 0 && device_may_wakeup(dev))
+		disable_irq_wake(rtc->irq);
+
+	return 0;
+}
+
+/* Unconditionally disable the alarm */
+static int lpc32xx_rtc_freeze(struct device *dev)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	spin_lock_irq(&rtc->lock);
+
+	rtc_writel(rtc, LPC32XX_RTC_CTRL,
+		rtc_readl(rtc, LPC32XX_RTC_CTRL) &
+			  ~LPC32XX_RTC_CTRL_MATCH0);
+
+	spin_unlock_irq(&rtc->lock);
+
+	return 0;
+}
+
+static int lpc32xx_rtc_thaw(struct device *dev)
+{
+	struct lpc32xx_rtc *rtc = dev_get_drvdata(dev);
+
+	if (rtc->alarm_enabled) {
+		spin_lock_irq(&rtc->lock);
+
+		rtc_writel(rtc, LPC32XX_RTC_CTRL,
+			   rtc_readl(rtc, LPC32XX_RTC_CTRL) |
+			   LPC32XX_RTC_CTRL_MATCH0);
+
+		spin_unlock_irq(&rtc->lock);
+	}
+
+	return 0;
+}
+
+static const struct dev_pm_ops lpc32xx_rtc_pm_ops = {
+	.suspend = lpc32xx_rtc_suspend,
+	.resume = lpc32xx_rtc_resume,
+	.freeze = lpc32xx_rtc_freeze,
+	.thaw = lpc32xx_rtc_thaw,
+	.restore = lpc32xx_rtc_resume
+};
+
+#define LPC32XX_RTC_PM_OPS (&lpc32xx_rtc_pm_ops)
+#else
+#define LPC32XX_RTC_PM_OPS NULL
+#endif
+
+#ifdef CONFIG_OF
+static const struct of_device_id lpc32xx_rtc_match[] = {
+	{ .compatible = "nxp,lpc3220-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, lpc32xx_rtc_match);
+#endif
+
+static struct platform_driver lpc32xx_rtc_driver = {
+	.probe		= lpc32xx_rtc_probe,
+	.driver = {
+		.name	= "rtc-lpc32xx",
+		.pm	= LPC32XX_RTC_PM_OPS,
+		.of_match_table = of_match_ptr(lpc32xx_rtc_match),
+	},
+};
+
+module_platform_driver(lpc32xx_rtc_driver);
+
+MODULE_AUTHOR("Kevin Wells <wellsk40@gmail.com");
+MODULE_DESCRIPTION("RTC driver for the LPC32xx SoC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:rtc-lpc32xx");