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, 517 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-rzn1.c b/drivers/rtc/rtc-rzn1.c
new file mode 100644
index 000000000..305f10a8a
--- /dev/null
+++ b/drivers/rtc/rtc-rzn1.c
@@ -0,0 +1,517 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Renesas RZ/N1 Real Time Clock interface for Linux
+ *
+ * Copyright:
+ * - 2014 Renesas Electronics Europe Limited
+ * - 2022 Schneider Electric
+ *
+ * Authors:
+ * - Michel Pollet <buserror@gmail.com>
+ * - Miquel Raynal <miquel.raynal@bootlin.com>
+ */
+
+#include <linux/bcd.h>
+#include <linux/clk.h>
+#include <linux/init.h>
+#include <linux/iopoll.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/pm_runtime.h>
+#include <linux/rtc.h>
+#include <linux/spinlock.h>
+
+#define RZN1_RTC_CTL0 0x00
+#define   RZN1_RTC_CTL0_SLSB_SCMP BIT(4)
+#define   RZN1_RTC_CTL0_AMPM BIT(5)
+#define   RZN1_RTC_CTL0_CEST BIT(6)
+#define   RZN1_RTC_CTL0_CE BIT(7)
+
+#define RZN1_RTC_CTL1 0x04
+#define   RZN1_RTC_CTL1_1SE BIT(3)
+#define   RZN1_RTC_CTL1_ALME BIT(4)
+
+#define RZN1_RTC_CTL2 0x08
+#define   RZN1_RTC_CTL2_WAIT BIT(0)
+#define   RZN1_RTC_CTL2_WST BIT(1)
+#define   RZN1_RTC_CTL2_WUST BIT(5)
+#define   RZN1_RTC_CTL2_STOPPED (RZN1_RTC_CTL2_WAIT | RZN1_RTC_CTL2_WST)
+
+#define RZN1_RTC_TIME 0x30
+#define RZN1_RTC_TIME_MIN_SHIFT 8
+#define RZN1_RTC_TIME_HOUR_SHIFT 16
+#define RZN1_RTC_CAL 0x34
+#define RZN1_RTC_CAL_DAY_SHIFT 8
+#define RZN1_RTC_CAL_MON_SHIFT 16
+#define RZN1_RTC_CAL_YEAR_SHIFT 24
+
+#define RZN1_RTC_SUBU 0x38
+#define   RZN1_RTC_SUBU_DEV BIT(7)
+#define   RZN1_RTC_SUBU_DECR BIT(6)
+
+#define RZN1_RTC_SCMP 0x3c
+
+#define RZN1_RTC_ALM 0x40
+#define RZN1_RTC_ALH 0x44
+#define RZN1_RTC_ALW 0x48
+
+#define RZN1_RTC_SECC 0x4c
+#define RZN1_RTC_TIMEC 0x68
+#define RZN1_RTC_CALC 0x6c
+
+struct rzn1_rtc {
+	struct rtc_device *rtcdev;
+	void __iomem *base;
+	/*
+	 * Protects access to RZN1_RTC_CTL1 reg. rtc_lock with threaded_irqs
+	 * would introduce race conditions when switching interrupts because
+	 * of potential sleeps
+	 */
+	spinlock_t ctl1_access_lock;
+	struct rtc_time tm_alarm;
+};
+
+static void rzn1_rtc_get_time_snapshot(struct rzn1_rtc *rtc, struct rtc_time *tm)
+{
+	u32 val;
+
+	val = readl(rtc->base + RZN1_RTC_TIMEC);
+	tm->tm_sec = bcd2bin(val);
+	tm->tm_min = bcd2bin(val >> RZN1_RTC_TIME_MIN_SHIFT);
+	tm->tm_hour = bcd2bin(val >> RZN1_RTC_TIME_HOUR_SHIFT);
+
+	val = readl(rtc->base + RZN1_RTC_CALC);
+	tm->tm_wday = val & 0x0f;
+	tm->tm_mday = bcd2bin(val >> RZN1_RTC_CAL_DAY_SHIFT);
+	tm->tm_mon = bcd2bin(val >> RZN1_RTC_CAL_MON_SHIFT) - 1;
+	tm->tm_year = bcd2bin(val >> RZN1_RTC_CAL_YEAR_SHIFT) + 100;
+}
+
+static int rzn1_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	u32 val, secs;
+
+	/*
+	 * The RTC was not started or is stopped and thus does not carry the
+	 * proper time/date.
+	 */
+	val = readl(rtc->base + RZN1_RTC_CTL2);
+	if (val & RZN1_RTC_CTL2_STOPPED)
+		return -EINVAL;
+
+	rzn1_rtc_get_time_snapshot(rtc, tm);
+	secs = readl(rtc->base + RZN1_RTC_SECC);
+	if (tm->tm_sec != bcd2bin(secs))
+		rzn1_rtc_get_time_snapshot(rtc, tm);
+
+	return 0;
+}
+
+static int rzn1_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	u32 val;
+	int ret;
+
+	val = readl(rtc->base + RZN1_RTC_CTL2);
+	if (!(val & RZN1_RTC_CTL2_STOPPED)) {
+		/* Hold the counter if it was counting up */
+		writel(RZN1_RTC_CTL2_WAIT, rtc->base + RZN1_RTC_CTL2);
+
+		/* Wait for the counter to stop: two 32k clock cycles */
+		usleep_range(61, 100);
+		ret = readl_poll_timeout(rtc->base + RZN1_RTC_CTL2, val,
+					 val & RZN1_RTC_CTL2_WST, 0, 100);
+		if (ret)
+			return ret;
+	}
+
+	val = bin2bcd(tm->tm_sec);
+	val |= bin2bcd(tm->tm_min) << RZN1_RTC_TIME_MIN_SHIFT;
+	val |= bin2bcd(tm->tm_hour) << RZN1_RTC_TIME_HOUR_SHIFT;
+	writel(val, rtc->base + RZN1_RTC_TIME);
+
+	val = tm->tm_wday;
+	val |= bin2bcd(tm->tm_mday) << RZN1_RTC_CAL_DAY_SHIFT;
+	val |= bin2bcd(tm->tm_mon + 1) << RZN1_RTC_CAL_MON_SHIFT;
+	val |= bin2bcd(tm->tm_year - 100) << RZN1_RTC_CAL_YEAR_SHIFT;
+	writel(val, rtc->base + RZN1_RTC_CAL);
+
+	writel(0, rtc->base + RZN1_RTC_CTL2);
+
+	return 0;
+}
+
+static irqreturn_t rzn1_rtc_alarm_irq(int irq, void *dev_id)
+{
+	struct rzn1_rtc *rtc = dev_id;
+	u32 ctl1, set_irq_bits = 0;
+
+	if (rtc->tm_alarm.tm_sec == 0)
+		rtc_update_irq(rtc->rtcdev, 1, RTC_AF | RTC_IRQF);
+	else
+		/* Switch to 1s interrupts */
+		set_irq_bits = RZN1_RTC_CTL1_1SE;
+
+	guard(spinlock)(&rtc->ctl1_access_lock);
+
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+	ctl1 &= ~RZN1_RTC_CTL1_ALME;
+	ctl1 |= set_irq_bits;
+	writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t rzn1_rtc_1s_irq(int irq, void *dev_id)
+{
+	struct rzn1_rtc *rtc = dev_id;
+	u32 ctl1;
+
+	if (readl(rtc->base + RZN1_RTC_SECC) == bin2bcd(rtc->tm_alarm.tm_sec)) {
+		guard(spinlock)(&rtc->ctl1_access_lock);
+
+		ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+		ctl1 &= ~RZN1_RTC_CTL1_1SE;
+		writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+
+		rtc_update_irq(rtc->rtcdev, 1, RTC_AF | RTC_IRQF);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static int rzn1_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time *tm = &rtc->tm_alarm, tm_now;
+	u32 ctl1;
+	int ret;
+
+	guard(spinlock_irqsave)(&rtc->ctl1_access_lock);
+
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+
+	if (enable) {
+		/*
+		 * Use alarm interrupt if alarm time is at least a minute away
+		 * or less than a minute but in the next minute. Otherwise use
+		 * 1 second interrupt to wait for the proper second
+		 */
+		do {
+			ctl1 &= ~(RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE);
+
+			ret = rzn1_rtc_read_time(dev, &tm_now);
+			if (ret)
+				return ret;
+
+			if (rtc_tm_sub(tm, &tm_now) > 59 || tm->tm_min != tm_now.tm_min)
+				ctl1 |= RZN1_RTC_CTL1_ALME;
+			else
+				ctl1 |= RZN1_RTC_CTL1_1SE;
+
+			writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+		} while (readl(rtc->base + RZN1_RTC_SECC) != bin2bcd(tm_now.tm_sec));
+	} else {
+		ctl1 &= ~(RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE);
+		writel(ctl1, rtc->base + RZN1_RTC_CTL1);
+	}
+
+	return 0;
+}
+
+static int rzn1_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time *tm = &alrm->time;
+	unsigned int min, hour, wday, delta_days;
+	time64_t alarm;
+	u32 ctl1;
+	int ret;
+
+	ret = rzn1_rtc_read_time(dev, tm);
+	if (ret)
+		return ret;
+
+	min = readl(rtc->base + RZN1_RTC_ALM);
+	hour = readl(rtc->base + RZN1_RTC_ALH);
+	wday = readl(rtc->base + RZN1_RTC_ALW);
+
+	tm->tm_sec = 0;
+	tm->tm_min = bcd2bin(min);
+	tm->tm_hour = bcd2bin(hour);
+	delta_days = ((fls(wday) - 1) - tm->tm_wday + 7) % 7;
+	tm->tm_wday = fls(wday) - 1;
+
+	if (delta_days) {
+		alarm = rtc_tm_to_time64(tm) + (delta_days * 86400);
+		rtc_time64_to_tm(alarm, tm);
+	}
+
+	ctl1 = readl(rtc->base + RZN1_RTC_CTL1);
+	alrm->enabled = !!(ctl1 & (RZN1_RTC_CTL1_ALME | RZN1_RTC_CTL1_1SE));
+
+	return 0;
+}
+
+static int rzn1_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time *tm = &alrm->time, tm_now;
+	unsigned long alarm, farest;
+	unsigned int days_ahead, wday;
+	int ret;
+
+	ret = rzn1_rtc_read_time(dev, &tm_now);
+	if (ret)
+		return ret;
+
+	/* We cannot set alarms more than one week ahead */
+	farest = rtc_tm_to_time64(&tm_now) + rtc->rtcdev->alarm_offset_max;
+	alarm = rtc_tm_to_time64(tm);
+	if (time_after(alarm, farest))
+		return -ERANGE;
+
+	/* Convert alarm day into week day */
+	days_ahead = tm->tm_mday - tm_now.tm_mday;
+	wday = (tm_now.tm_wday + days_ahead) % 7;
+
+	writel(bin2bcd(tm->tm_min), rtc->base + RZN1_RTC_ALM);
+	writel(bin2bcd(tm->tm_hour), rtc->base + RZN1_RTC_ALH);
+	writel(BIT(wday), rtc->base + RZN1_RTC_ALW);
+
+	rtc->tm_alarm = alrm->time;
+
+	rzn1_rtc_alarm_irq_enable(dev, alrm->enabled);
+
+	return 0;
+}
+
+static int rzn1_rtc_read_offset(struct device *dev, long *offset)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	unsigned int ppb_per_step;
+	bool subtract;
+	u32 val;
+
+	val = readl(rtc->base + RZN1_RTC_SUBU);
+	ppb_per_step = val & RZN1_RTC_SUBU_DEV ? 1017 : 3051;
+	subtract = val & RZN1_RTC_SUBU_DECR;
+	val &= 0x3F;
+
+	if (!val)
+		*offset = 0;
+	else if (subtract)
+		*offset = -(((~val) & 0x3F) + 1) * ppb_per_step;
+	else
+		*offset = (val - 1) * ppb_per_step;
+
+	return 0;
+}
+
+static int rzn1_rtc_set_offset(struct device *dev, long offset)
+{
+	struct rzn1_rtc *rtc = dev_get_drvdata(dev);
+	int stepsh, stepsl, steps;
+	u32 subu = 0, ctl2;
+	int ret;
+
+	/*
+	 * Check which resolution mode (every 20 or 60s) can be used.
+	 * Between 2 and 124 clock pulses can be added or substracted.
+	 *
+	 * In 20s mode, the minimum resolution is 2 / (32768 * 20) which is
+	 * close to 3051 ppb. In 60s mode, the resolution is closer to 1017.
+	 */
+	stepsh = DIV_ROUND_CLOSEST(offset, 1017);
+	stepsl = DIV_ROUND_CLOSEST(offset, 3051);
+
+	if (stepsh >= -0x3E && stepsh <= 0x3E) {
+		/* 1017 ppb per step */
+		steps = stepsh;
+		subu |= RZN1_RTC_SUBU_DEV;
+	} else if (stepsl >= -0x3E && stepsl <= 0x3E) {
+		/* 3051 ppb per step */
+		steps = stepsl;
+	} else {
+		return -ERANGE;
+	}
+
+	if (!steps)
+		return 0;
+
+	if (steps > 0) {
+		subu |= steps + 1;
+	} else {
+		subu |= RZN1_RTC_SUBU_DECR;
+		subu |= (~(-steps - 1)) & 0x3F;
+	}
+
+	ret = readl_poll_timeout(rtc->base + RZN1_RTC_CTL2, ctl2,
+				 !(ctl2 & RZN1_RTC_CTL2_WUST), 100, 2000000);
+	if (ret)
+		return ret;
+
+	writel(subu, rtc->base + RZN1_RTC_SUBU);
+
+	return 0;
+}
+
+static const struct rtc_class_ops rzn1_rtc_ops_subu = {
+	.read_time = rzn1_rtc_read_time,
+	.set_time = rzn1_rtc_set_time,
+	.read_alarm = rzn1_rtc_read_alarm,
+	.set_alarm = rzn1_rtc_set_alarm,
+	.alarm_irq_enable = rzn1_rtc_alarm_irq_enable,
+	.read_offset = rzn1_rtc_read_offset,
+	.set_offset = rzn1_rtc_set_offset,
+};
+
+static const struct rtc_class_ops rzn1_rtc_ops_scmp = {
+	.read_time = rzn1_rtc_read_time,
+	.set_time = rzn1_rtc_set_time,
+	.read_alarm = rzn1_rtc_read_alarm,
+	.set_alarm = rzn1_rtc_set_alarm,
+	.alarm_irq_enable = rzn1_rtc_alarm_irq_enable,
+};
+
+static int rzn1_rtc_probe(struct platform_device *pdev)
+{
+	struct rzn1_rtc *rtc;
+	u32 val, scmp_val = 0;
+	struct clk *xtal;
+	unsigned long rate;
+	int irq, ret;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, rtc);
+
+	rtc->base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rtc->base))
+		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->base), "Missing reg\n");
+
+	irq = platform_get_irq_byname(pdev, "alarm");
+	if (irq < 0)
+		return irq;
+
+	rtc->rtcdev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtcdev))
+		return PTR_ERR(rtc->rtcdev);
+
+	rtc->rtcdev->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rtc->rtcdev->range_max = RTC_TIMESTAMP_END_2099;
+	rtc->rtcdev->alarm_offset_max = 7 * 86400;
+
+	ret = devm_pm_runtime_enable(&pdev->dev);
+	if (ret < 0)
+		return ret;
+	ret = pm_runtime_resume_and_get(&pdev->dev);
+	if (ret < 0)
+		return ret;
+
+	/* Only switch to scmp if we have an xtal clock with a valid rate and != 32768 */
+	xtal = devm_clk_get_optional(&pdev->dev, "xtal");
+	if (IS_ERR(xtal)) {
+		ret = PTR_ERR(xtal);
+		goto dis_runtime_pm;
+	} else if (xtal) {
+		rate = clk_get_rate(xtal);
+
+		if (rate < 32000 || rate > BIT(22)) {
+			ret = -EOPNOTSUPP;
+			goto dis_runtime_pm;
+		}
+
+		if (rate != 32768)
+			scmp_val = RZN1_RTC_CTL0_SLSB_SCMP;
+	}
+
+	/* Disable controller during SUBU/SCMP setup */
+	val = readl(rtc->base + RZN1_RTC_CTL0) & ~RZN1_RTC_CTL0_CE;
+	writel(val, rtc->base + RZN1_RTC_CTL0);
+	/* Wait 2-4 32k clock cycles for the disabled controller */
+	ret = readl_poll_timeout(rtc->base + RZN1_RTC_CTL0, val,
+				 !(val & RZN1_RTC_CTL0_CEST), 62, 123);
+	if (ret)
+		goto dis_runtime_pm;
+
+	/* Set desired modes leaving the controller disabled */
+	writel(RZN1_RTC_CTL0_AMPM | scmp_val, rtc->base + RZN1_RTC_CTL0);
+
+	if (scmp_val) {
+		writel(rate - 1, rtc->base + RZN1_RTC_SCMP);
+		rtc->rtcdev->ops = &rzn1_rtc_ops_scmp;
+	} else {
+		rtc->rtcdev->ops = &rzn1_rtc_ops_subu;
+	}
+
+	/* Enable controller finally */
+	writel(RZN1_RTC_CTL0_CE | RZN1_RTC_CTL0_AMPM | scmp_val, rtc->base + RZN1_RTC_CTL0);
+
+	/* Disable all interrupts */
+	writel(0, rtc->base + RZN1_RTC_CTL1);
+
+	spin_lock_init(&rtc->ctl1_access_lock);
+
+	ret = devm_request_irq(&pdev->dev, irq, rzn1_rtc_alarm_irq, 0, "RZN1 RTC Alarm", rtc);
+	if (ret) {
+		dev_err(&pdev->dev, "RTC alarm interrupt not available\n");
+		goto dis_runtime_pm;
+	}
+
+	irq = platform_get_irq_byname_optional(pdev, "pps");
+	if (irq >= 0)
+		ret = devm_request_irq(&pdev->dev, irq, rzn1_rtc_1s_irq, 0, "RZN1 RTC 1s", rtc);
+
+	if (irq < 0 || ret) {
+		set_bit(RTC_FEATURE_ALARM_RES_MINUTE, rtc->rtcdev->features);
+		clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->rtcdev->features);
+		dev_warn(&pdev->dev, "RTC pps interrupt not available. Alarm has only minute accuracy\n");
+	}
+
+	ret = devm_rtc_register_device(rtc->rtcdev);
+	if (ret)
+		goto dis_runtime_pm;
+
+	return 0;
+
+dis_runtime_pm:
+	pm_runtime_put(&pdev->dev);
+
+	return ret;
+}
+
+static void rzn1_rtc_remove(struct platform_device *pdev)
+{
+	struct rzn1_rtc *rtc = platform_get_drvdata(pdev);
+
+	/* Disable all interrupts */
+	writel(0, rtc->base + RZN1_RTC_CTL1);
+
+	pm_runtime_put(&pdev->dev);
+}
+
+static const struct of_device_id rzn1_rtc_of_match[] = {
+	{ .compatible	= "renesas,rzn1-rtc" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, rzn1_rtc_of_match);
+
+static struct platform_driver rzn1_rtc_driver = {
+	.probe = rzn1_rtc_probe,
+	.remove = rzn1_rtc_remove,
+	.driver = {
+		.name	= "rzn1-rtc",
+		.of_match_table = rzn1_rtc_of_match,
+	},
+};
+module_platform_driver(rzn1_rtc_driver);
+
+MODULE_AUTHOR("Michel Pollet <buserror@gmail.com>");
+MODULE_AUTHOR("Miquel Raynal <miquel.raynal@bootlin.com");
+MODULE_DESCRIPTION("RZ/N1 RTC driver");
+MODULE_LICENSE("GPL");