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, 412 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-cadence.c b/drivers/rtc/rtc-cadence.c
new file mode 100644
index 000000000..8634eea79
--- /dev/null
+++ b/drivers/rtc/rtc-cadence.c
@@ -0,0 +1,412 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2019 Cadence
+ *
+ * Authors:
+ *  Jan Kotas <jank@cadence.com>
+ */
+
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/of.h>
+#include <linux/io.h>
+#include <linux/rtc.h>
+#include <linux/clk.h>
+#include <linux/bcd.h>
+#include <linux/bitfield.h>
+#include <linux/interrupt.h>
+#include <linux/pm_wakeirq.h>
+
+/* Registers */
+#define CDNS_RTC_CTLR		0x00
+#define CDNS_RTC_HMR		0x04
+#define CDNS_RTC_TIMR		0x08
+#define CDNS_RTC_CALR		0x0C
+#define CDNS_RTC_TIMAR		0x10
+#define CDNS_RTC_CALAR		0x14
+#define CDNS_RTC_AENR		0x18
+#define CDNS_RTC_EFLR		0x1C
+#define CDNS_RTC_IENR		0x20
+#define CDNS_RTC_IDISR		0x24
+#define CDNS_RTC_IMSKR		0x28
+#define CDNS_RTC_STSR		0x2C
+#define CDNS_RTC_KRTCR		0x30
+
+/* Control */
+#define CDNS_RTC_CTLR_TIME	BIT(0)
+#define CDNS_RTC_CTLR_CAL	BIT(1)
+#define CDNS_RTC_CTLR_TIME_CAL	(CDNS_RTC_CTLR_TIME | CDNS_RTC_CTLR_CAL)
+
+/* Status */
+#define CDNS_RTC_STSR_VT	BIT(0)
+#define CDNS_RTC_STSR_VC	BIT(1)
+#define CDNS_RTC_STSR_VTA	BIT(2)
+#define CDNS_RTC_STSR_VCA	BIT(3)
+#define CDNS_RTC_STSR_VT_VC	(CDNS_RTC_STSR_VT | CDNS_RTC_STSR_VC)
+#define CDNS_RTC_STSR_VTA_VCA	(CDNS_RTC_STSR_VTA | CDNS_RTC_STSR_VCA)
+
+/* Keep RTC */
+#define CDNS_RTC_KRTCR_KRTC	BIT(0)
+
+/* Alarm, Event, Interrupt */
+#define CDNS_RTC_AEI_HOS	BIT(0)
+#define CDNS_RTC_AEI_SEC	BIT(1)
+#define CDNS_RTC_AEI_MIN	BIT(2)
+#define CDNS_RTC_AEI_HOUR	BIT(3)
+#define CDNS_RTC_AEI_DATE	BIT(4)
+#define CDNS_RTC_AEI_MNTH	BIT(5)
+#define CDNS_RTC_AEI_ALRM	BIT(6)
+
+/* Time */
+#define CDNS_RTC_TIME_H		GENMASK(7, 0)
+#define CDNS_RTC_TIME_S		GENMASK(14, 8)
+#define CDNS_RTC_TIME_M		GENMASK(22, 16)
+#define CDNS_RTC_TIME_HR	GENMASK(29, 24)
+#define CDNS_RTC_TIME_PM	BIT(30)
+#define CDNS_RTC_TIME_CH	BIT(31)
+
+/* Calendar */
+#define CDNS_RTC_CAL_DAY	GENMASK(2, 0)
+#define CDNS_RTC_CAL_M		GENMASK(7, 3)
+#define CDNS_RTC_CAL_D		GENMASK(13, 8)
+#define CDNS_RTC_CAL_Y		GENMASK(23, 16)
+#define CDNS_RTC_CAL_C		GENMASK(29, 24)
+#define CDNS_RTC_CAL_CH		BIT(31)
+
+#define CDNS_RTC_MAX_REGS_TRIES	3
+
+struct cdns_rtc {
+	struct rtc_device *rtc_dev;
+	struct clk *pclk;
+	struct clk *ref_clk;
+	void __iomem *regs;
+	int irq;
+};
+
+static void cdns_rtc_set_enabled(struct cdns_rtc *crtc, bool enabled)
+{
+	u32 reg = enabled ? 0x0 : CDNS_RTC_CTLR_TIME_CAL;
+
+	writel(reg, crtc->regs + CDNS_RTC_CTLR);
+}
+
+static bool cdns_rtc_get_enabled(struct cdns_rtc *crtc)
+{
+	return !(readl(crtc->regs + CDNS_RTC_CTLR) & CDNS_RTC_CTLR_TIME_CAL);
+}
+
+static irqreturn_t cdns_rtc_irq_handler(int irq, void *id)
+{
+	struct device *dev = id;
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+
+	/* Reading the register clears it */
+	if (!(readl(crtc->regs + CDNS_RTC_EFLR) & CDNS_RTC_AEI_ALRM))
+		return IRQ_NONE;
+
+	rtc_update_irq(crtc->rtc_dev, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static u32 cdns_rtc_time2reg(struct rtc_time *tm)
+{
+	return FIELD_PREP(CDNS_RTC_TIME_S,  bin2bcd(tm->tm_sec))
+	     | FIELD_PREP(CDNS_RTC_TIME_M,  bin2bcd(tm->tm_min))
+	     | FIELD_PREP(CDNS_RTC_TIME_HR, bin2bcd(tm->tm_hour));
+}
+
+static void cdns_rtc_reg2time(u32 reg, struct rtc_time *tm)
+{
+	tm->tm_sec  = bcd2bin(FIELD_GET(CDNS_RTC_TIME_S, reg));
+	tm->tm_min  = bcd2bin(FIELD_GET(CDNS_RTC_TIME_M, reg));
+	tm->tm_hour = bcd2bin(FIELD_GET(CDNS_RTC_TIME_HR, reg));
+}
+
+static int cdns_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+	u32 reg;
+
+	/* If the RTC is disabled, assume the values are invalid */
+	if (!cdns_rtc_get_enabled(crtc))
+		return -EINVAL;
+
+	cdns_rtc_set_enabled(crtc, false);
+
+	reg = readl(crtc->regs + CDNS_RTC_TIMR);
+	cdns_rtc_reg2time(reg, tm);
+
+	reg = readl(crtc->regs + CDNS_RTC_CALR);
+	tm->tm_mday = bcd2bin(FIELD_GET(CDNS_RTC_CAL_D, reg));
+	tm->tm_mon  = bcd2bin(FIELD_GET(CDNS_RTC_CAL_M, reg)) - 1;
+	tm->tm_year = bcd2bin(FIELD_GET(CDNS_RTC_CAL_Y, reg))
+		    + bcd2bin(FIELD_GET(CDNS_RTC_CAL_C, reg)) * 100 - 1900;
+	tm->tm_wday = bcd2bin(FIELD_GET(CDNS_RTC_CAL_DAY, reg)) - 1;
+
+	cdns_rtc_set_enabled(crtc, true);
+	return 0;
+}
+
+static int cdns_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+	u32 timr, calr, stsr;
+	int ret = -EIO;
+	int year = tm->tm_year + 1900;
+	int tries;
+
+	cdns_rtc_set_enabled(crtc, false);
+
+	timr = cdns_rtc_time2reg(tm);
+
+	calr = FIELD_PREP(CDNS_RTC_CAL_D, bin2bcd(tm->tm_mday))
+	     | FIELD_PREP(CDNS_RTC_CAL_M, bin2bcd(tm->tm_mon + 1))
+	     | FIELD_PREP(CDNS_RTC_CAL_Y, bin2bcd(year % 100))
+	     | FIELD_PREP(CDNS_RTC_CAL_C, bin2bcd(year / 100))
+	     | FIELD_PREP(CDNS_RTC_CAL_DAY, tm->tm_wday + 1);
+
+	/* Update registers, check valid flags */
+	for (tries = 0; tries < CDNS_RTC_MAX_REGS_TRIES; tries++) {
+		writel(timr, crtc->regs + CDNS_RTC_TIMR);
+		writel(calr, crtc->regs + CDNS_RTC_CALR);
+		stsr = readl(crtc->regs + CDNS_RTC_STSR);
+
+		if ((stsr & CDNS_RTC_STSR_VT_VC) == CDNS_RTC_STSR_VT_VC) {
+			ret = 0;
+			break;
+		}
+	}
+
+	cdns_rtc_set_enabled(crtc, true);
+	return ret;
+}
+
+static int cdns_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+
+	if (enabled) {
+		writel((CDNS_RTC_AEI_SEC | CDNS_RTC_AEI_MIN | CDNS_RTC_AEI_HOUR
+			| CDNS_RTC_AEI_DATE | CDNS_RTC_AEI_MNTH),
+		       crtc->regs + CDNS_RTC_AENR);
+		writel(CDNS_RTC_AEI_ALRM, crtc->regs + CDNS_RTC_IENR);
+	} else {
+		writel(0, crtc->regs + CDNS_RTC_AENR);
+		writel(CDNS_RTC_AEI_ALRM, crtc->regs + CDNS_RTC_IDISR);
+	}
+
+	return 0;
+}
+
+static int cdns_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+	u32 reg;
+
+	reg = readl(crtc->regs + CDNS_RTC_TIMAR);
+	cdns_rtc_reg2time(reg, &alarm->time);
+
+	reg = readl(crtc->regs + CDNS_RTC_CALAR);
+	alarm->time.tm_mday = bcd2bin(FIELD_GET(CDNS_RTC_CAL_D, reg));
+	alarm->time.tm_mon  = bcd2bin(FIELD_GET(CDNS_RTC_CAL_M, reg)) - 1;
+
+	return 0;
+}
+
+static int cdns_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+	int ret = -EIO;
+	int tries;
+	u32 timar, calar, stsr;
+
+	cdns_rtc_alarm_irq_enable(dev, 0);
+
+	timar = cdns_rtc_time2reg(&alarm->time);
+	calar = FIELD_PREP(CDNS_RTC_CAL_D, bin2bcd(alarm->time.tm_mday))
+	      | FIELD_PREP(CDNS_RTC_CAL_M, bin2bcd(alarm->time.tm_mon + 1));
+
+	/* Update registers, check valid alarm flags */
+	for (tries = 0; tries < CDNS_RTC_MAX_REGS_TRIES; tries++) {
+		writel(timar, crtc->regs + CDNS_RTC_TIMAR);
+		writel(calar, crtc->regs + CDNS_RTC_CALAR);
+		stsr = readl(crtc->regs + CDNS_RTC_STSR);
+
+		if ((stsr & CDNS_RTC_STSR_VTA_VCA) == CDNS_RTC_STSR_VTA_VCA) {
+			ret = 0;
+			break;
+		}
+	}
+
+	if (!ret)
+		cdns_rtc_alarm_irq_enable(dev, alarm->enabled);
+	return ret;
+}
+
+static const struct rtc_class_ops cdns_rtc_ops = {
+	.read_time	= cdns_rtc_read_time,
+	.set_time	= cdns_rtc_set_time,
+	.read_alarm	= cdns_rtc_read_alarm,
+	.set_alarm	= cdns_rtc_set_alarm,
+	.alarm_irq_enable = cdns_rtc_alarm_irq_enable,
+};
+
+static int cdns_rtc_probe(struct platform_device *pdev)
+{
+	struct cdns_rtc *crtc;
+	int ret;
+	unsigned long ref_clk_freq;
+
+	crtc = devm_kzalloc(&pdev->dev, sizeof(*crtc), GFP_KERNEL);
+	if (!crtc)
+		return -ENOMEM;
+
+	crtc->regs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(crtc->regs))
+		return PTR_ERR(crtc->regs);
+
+	crtc->irq = platform_get_irq(pdev, 0);
+	if (crtc->irq < 0)
+		return -EINVAL;
+
+	crtc->pclk = devm_clk_get(&pdev->dev, "pclk");
+	if (IS_ERR(crtc->pclk)) {
+		ret = PTR_ERR(crtc->pclk);
+		dev_err(&pdev->dev,
+			"Failed to retrieve the peripheral clock, %d\n", ret);
+		return ret;
+	}
+
+	crtc->ref_clk = devm_clk_get(&pdev->dev, "ref_clk");
+	if (IS_ERR(crtc->ref_clk)) {
+		ret = PTR_ERR(crtc->ref_clk);
+		dev_err(&pdev->dev,
+			"Failed to retrieve the reference clock, %d\n", ret);
+		return ret;
+	}
+
+	crtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(crtc->rtc_dev))
+		return PTR_ERR(crtc->rtc_dev);
+
+	platform_set_drvdata(pdev, crtc);
+
+	ret = clk_prepare_enable(crtc->pclk);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"Failed to enable the peripheral clock, %d\n", ret);
+		return ret;
+	}
+
+	ret = clk_prepare_enable(crtc->ref_clk);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"Failed to enable the reference clock, %d\n", ret);
+		goto err_disable_pclk;
+	}
+
+	ref_clk_freq = clk_get_rate(crtc->ref_clk);
+	if ((ref_clk_freq != 1) && (ref_clk_freq != 100)) {
+		dev_err(&pdev->dev,
+			"Invalid reference clock frequency %lu Hz.\n",
+			ref_clk_freq);
+		ret = -EINVAL;
+		goto err_disable_ref_clk;
+	}
+
+	ret = devm_request_irq(&pdev->dev, crtc->irq,
+			       cdns_rtc_irq_handler, 0,
+			       dev_name(&pdev->dev), &pdev->dev);
+	if (ret) {
+		dev_err(&pdev->dev,
+			"Failed to request interrupt for the device, %d\n",
+			ret);
+		goto err_disable_ref_clk;
+	}
+
+	/* The RTC supports 01.01.1900 - 31.12.2999 */
+	crtc->rtc_dev->range_min = mktime64(1900,  1,  1,  0,  0,  0);
+	crtc->rtc_dev->range_max = mktime64(2999, 12, 31, 23, 59, 59);
+
+	crtc->rtc_dev->ops = &cdns_rtc_ops;
+	device_init_wakeup(&pdev->dev, true);
+
+	/* Always use 24-hour mode and keep the RTC values */
+	writel(0, crtc->regs + CDNS_RTC_HMR);
+	writel(CDNS_RTC_KRTCR_KRTC, crtc->regs + CDNS_RTC_KRTCR);
+
+	ret = devm_rtc_register_device(crtc->rtc_dev);
+	if (ret)
+		goto err_disable_wakeup;
+
+	return 0;
+
+err_disable_wakeup:
+	device_init_wakeup(&pdev->dev, false);
+
+err_disable_ref_clk:
+	clk_disable_unprepare(crtc->ref_clk);
+
+err_disable_pclk:
+	clk_disable_unprepare(crtc->pclk);
+
+	return ret;
+}
+
+static void cdns_rtc_remove(struct platform_device *pdev)
+{
+	struct cdns_rtc *crtc = platform_get_drvdata(pdev);
+
+	cdns_rtc_alarm_irq_enable(&pdev->dev, 0);
+	device_init_wakeup(&pdev->dev, false);
+
+	clk_disable_unprepare(crtc->pclk);
+	clk_disable_unprepare(crtc->ref_clk);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int cdns_rtc_suspend(struct device *dev)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(crtc->irq);
+
+	return 0;
+}
+
+static int cdns_rtc_resume(struct device *dev)
+{
+	struct cdns_rtc *crtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(crtc->irq);
+
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(cdns_rtc_pm_ops, cdns_rtc_suspend, cdns_rtc_resume);
+
+static const struct of_device_id cdns_rtc_of_match[] = {
+	{ .compatible = "cdns,rtc-r109v3" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, cdns_rtc_of_match);
+
+static struct platform_driver cdns_rtc_driver = {
+	.driver = {
+		.name = "cdns-rtc",
+		.of_match_table = cdns_rtc_of_match,
+		.pm = &cdns_rtc_pm_ops,
+	},
+	.probe = cdns_rtc_probe,
+	.remove = cdns_rtc_remove,
+};
+module_platform_driver(cdns_rtc_driver);
+
+MODULE_AUTHOR("Jan Kotas <jank@cadence.com>");
+MODULE_DESCRIPTION("Cadence RTC driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("platform:cdns-rtc");