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, 479 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-r7301.c b/drivers/rtc/rtc-r7301.c
new file mode 100644
index 000000000..6323b7771
--- /dev/null
+++ b/drivers/rtc/rtc-r7301.c
@@ -0,0 +1,479 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * EPSON TOYOCOM RTC-7301SF/DG Driver
+ *
+ * Copyright (c) 2016 Akinobu Mita <akinobu.mita@gmail.com>
+ *
+ * Based on rtc-rp5c01.c
+ *
+ * Datasheet: http://www5.epsondevice.com/en/products/parallel/rtc7301sf.html
+ */
+
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/delay.h>
+#include <linux/property.h>
+#include <linux/regmap.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#define DRV_NAME "rtc-r7301"
+
+#define RTC7301_1_SEC		0x0	/* Bank 0 and Band 1 */
+#define RTC7301_10_SEC		0x1	/* Bank 0 and Band 1 */
+#define RTC7301_AE		BIT(3)
+#define RTC7301_1_MIN		0x2	/* Bank 0 and Band 1 */
+#define RTC7301_10_MIN		0x3	/* Bank 0 and Band 1 */
+#define RTC7301_1_HOUR		0x4	/* Bank 0 and Band 1 */
+#define RTC7301_10_HOUR		0x5	/* Bank 0 and Band 1 */
+#define RTC7301_DAY_OF_WEEK	0x6	/* Bank 0 and Band 1 */
+#define RTC7301_1_DAY		0x7	/* Bank 0 and Band 1 */
+#define RTC7301_10_DAY		0x8	/* Bank 0 and Band 1 */
+#define RTC7301_1_MONTH		0x9	/* Bank 0 */
+#define RTC7301_10_MONTH	0xa	/* Bank 0 */
+#define RTC7301_1_YEAR		0xb	/* Bank 0 */
+#define RTC7301_10_YEAR		0xc	/* Bank 0 */
+#define RTC7301_100_YEAR	0xd	/* Bank 0 */
+#define RTC7301_1000_YEAR	0xe	/* Bank 0 */
+#define RTC7301_ALARM_CONTROL	0xe	/* Bank 1 */
+#define RTC7301_ALARM_CONTROL_AIE	BIT(0)
+#define RTC7301_ALARM_CONTROL_AF	BIT(1)
+#define RTC7301_TIMER_CONTROL	0xe	/* Bank 2 */
+#define RTC7301_TIMER_CONTROL_TIE	BIT(0)
+#define RTC7301_TIMER_CONTROL_TF	BIT(1)
+#define RTC7301_CONTROL		0xf	/* All banks */
+#define RTC7301_CONTROL_BUSY		BIT(0)
+#define RTC7301_CONTROL_STOP		BIT(1)
+#define RTC7301_CONTROL_BANK_SEL_0	BIT(2)
+#define RTC7301_CONTROL_BANK_SEL_1	BIT(3)
+
+struct rtc7301_priv {
+	struct regmap *regmap;
+	int irq;
+	spinlock_t lock;
+	u8 bank;
+};
+
+/*
+ * When the device is memory-mapped, some platforms pack the registers into
+ * 32-bit access using the lower 8 bits at each 4-byte stride, while others
+ * expose them as simply consecutive bytes.
+ */
+static const struct regmap_config rtc7301_regmap_32_config = {
+	.reg_bits = 32,
+	.val_bits = 8,
+	.reg_stride = 4,
+};
+
+static const struct regmap_config rtc7301_regmap_8_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.reg_stride = 1,
+};
+
+static u8 rtc7301_read(struct rtc7301_priv *priv, unsigned int reg)
+{
+	int reg_stride = regmap_get_reg_stride(priv->regmap);
+	unsigned int val;
+
+	regmap_read(priv->regmap, reg_stride * reg, &val);
+
+	return val & 0xf;
+}
+
+static void rtc7301_write(struct rtc7301_priv *priv, u8 val, unsigned int reg)
+{
+	int reg_stride = regmap_get_reg_stride(priv->regmap);
+
+	regmap_write(priv->regmap, reg_stride * reg, val);
+}
+
+static void rtc7301_update_bits(struct rtc7301_priv *priv, unsigned int reg,
+				u8 mask, u8 val)
+{
+	int reg_stride = regmap_get_reg_stride(priv->regmap);
+
+	regmap_update_bits(priv->regmap, reg_stride * reg, mask, val);
+}
+
+static int rtc7301_wait_while_busy(struct rtc7301_priv *priv)
+{
+	int retries = 100;
+
+	while (retries-- > 0) {
+		u8 val;
+
+		val = rtc7301_read(priv, RTC7301_CONTROL);
+		if (!(val & RTC7301_CONTROL_BUSY))
+			return 0;
+
+		udelay(300);
+	}
+
+	return -ETIMEDOUT;
+}
+
+static void rtc7301_stop(struct rtc7301_priv *priv)
+{
+	rtc7301_update_bits(priv, RTC7301_CONTROL, RTC7301_CONTROL_STOP,
+			    RTC7301_CONTROL_STOP);
+}
+
+static void rtc7301_start(struct rtc7301_priv *priv)
+{
+	rtc7301_update_bits(priv, RTC7301_CONTROL, RTC7301_CONTROL_STOP, 0);
+}
+
+static void rtc7301_select_bank(struct rtc7301_priv *priv, u8 bank)
+{
+	u8 val = 0;
+
+	if (bank == priv->bank)
+		return;
+
+	if (bank & BIT(0))
+		val |= RTC7301_CONTROL_BANK_SEL_0;
+	if (bank & BIT(1))
+		val |= RTC7301_CONTROL_BANK_SEL_1;
+
+	rtc7301_update_bits(priv, RTC7301_CONTROL,
+			    RTC7301_CONTROL_BANK_SEL_0 |
+			    RTC7301_CONTROL_BANK_SEL_1, val);
+
+	priv->bank = bank;
+}
+
+static void rtc7301_get_time(struct rtc7301_priv *priv, struct rtc_time *tm,
+			     bool alarm)
+{
+	int year;
+
+	tm->tm_sec = rtc7301_read(priv, RTC7301_1_SEC);
+	tm->tm_sec += (rtc7301_read(priv, RTC7301_10_SEC) & ~RTC7301_AE) * 10;
+	tm->tm_min = rtc7301_read(priv, RTC7301_1_MIN);
+	tm->tm_min += (rtc7301_read(priv, RTC7301_10_MIN) & ~RTC7301_AE) * 10;
+	tm->tm_hour = rtc7301_read(priv, RTC7301_1_HOUR);
+	tm->tm_hour += (rtc7301_read(priv, RTC7301_10_HOUR) & ~RTC7301_AE) * 10;
+	tm->tm_mday = rtc7301_read(priv, RTC7301_1_DAY);
+	tm->tm_mday += (rtc7301_read(priv, RTC7301_10_DAY) & ~RTC7301_AE) * 10;
+
+	if (alarm) {
+		tm->tm_wday = -1;
+		tm->tm_mon = -1;
+		tm->tm_year = -1;
+		tm->tm_yday = -1;
+		tm->tm_isdst = -1;
+		return;
+	}
+
+	tm->tm_wday = (rtc7301_read(priv, RTC7301_DAY_OF_WEEK) & ~RTC7301_AE);
+	tm->tm_mon = rtc7301_read(priv, RTC7301_10_MONTH) * 10 +
+		     rtc7301_read(priv, RTC7301_1_MONTH) - 1;
+	year = rtc7301_read(priv, RTC7301_1000_YEAR) * 1000 +
+	       rtc7301_read(priv, RTC7301_100_YEAR) * 100 +
+	       rtc7301_read(priv, RTC7301_10_YEAR) * 10 +
+	       rtc7301_read(priv, RTC7301_1_YEAR);
+
+	tm->tm_year = year - 1900;
+}
+
+static void rtc7301_write_time(struct rtc7301_priv *priv, struct rtc_time *tm,
+			       bool alarm)
+{
+	int year;
+
+	rtc7301_write(priv, tm->tm_sec % 10, RTC7301_1_SEC);
+	rtc7301_write(priv, tm->tm_sec / 10, RTC7301_10_SEC);
+
+	rtc7301_write(priv, tm->tm_min % 10, RTC7301_1_MIN);
+	rtc7301_write(priv, tm->tm_min / 10, RTC7301_10_MIN);
+
+	rtc7301_write(priv, tm->tm_hour % 10, RTC7301_1_HOUR);
+	rtc7301_write(priv, tm->tm_hour / 10, RTC7301_10_HOUR);
+
+	rtc7301_write(priv, tm->tm_mday % 10, RTC7301_1_DAY);
+	rtc7301_write(priv, tm->tm_mday / 10, RTC7301_10_DAY);
+
+	/* Don't care for alarm register */
+	rtc7301_write(priv, alarm ? RTC7301_AE : tm->tm_wday,
+		      RTC7301_DAY_OF_WEEK);
+
+	if (alarm)
+		return;
+
+	rtc7301_write(priv, (tm->tm_mon + 1) % 10, RTC7301_1_MONTH);
+	rtc7301_write(priv, (tm->tm_mon + 1) / 10, RTC7301_10_MONTH);
+
+	year = tm->tm_year + 1900;
+
+	rtc7301_write(priv, year % 10, RTC7301_1_YEAR);
+	rtc7301_write(priv, (year / 10) % 10, RTC7301_10_YEAR);
+	rtc7301_write(priv, (year / 100) % 10, RTC7301_100_YEAR);
+	rtc7301_write(priv, year / 1000, RTC7301_1000_YEAR);
+}
+
+static void rtc7301_alarm_irq(struct rtc7301_priv *priv, unsigned int enabled)
+{
+	rtc7301_update_bits(priv, RTC7301_ALARM_CONTROL,
+			    RTC7301_ALARM_CONTROL_AF |
+			    RTC7301_ALARM_CONTROL_AIE,
+			    enabled ? RTC7301_ALARM_CONTROL_AIE : 0);
+}
+
+static int rtc7301_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	int err;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_select_bank(priv, 0);
+
+	err = rtc7301_wait_while_busy(priv);
+	if (!err)
+		rtc7301_get_time(priv, tm, false);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return err;
+}
+
+static int rtc7301_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_stop(priv);
+	udelay(300);
+	rtc7301_select_bank(priv, 0);
+	rtc7301_write_time(priv, tm, false);
+	rtc7301_start(priv);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+static int rtc7301_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	u8 alrm_ctrl;
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_select_bank(priv, 1);
+	rtc7301_get_time(priv, &alarm->time, true);
+
+	alrm_ctrl = rtc7301_read(priv, RTC7301_ALARM_CONTROL);
+
+	alarm->enabled = !!(alrm_ctrl & RTC7301_ALARM_CONTROL_AIE);
+	alarm->pending = !!(alrm_ctrl & RTC7301_ALARM_CONTROL_AF);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+static int rtc7301_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_select_bank(priv, 1);
+	rtc7301_write_time(priv, &alarm->time, true);
+	rtc7301_alarm_irq(priv, alarm->enabled);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+static int rtc7301_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_select_bank(priv, 1);
+	rtc7301_alarm_irq(priv, enabled);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+static const struct rtc_class_ops rtc7301_rtc_ops = {
+	.read_time	= rtc7301_read_time,
+	.set_time	= rtc7301_set_time,
+	.read_alarm	= rtc7301_read_alarm,
+	.set_alarm	= rtc7301_set_alarm,
+	.alarm_irq_enable = rtc7301_alarm_irq_enable,
+};
+
+static irqreturn_t rtc7301_irq_handler(int irq, void *dev_id)
+{
+	struct rtc_device *rtc = dev_id;
+	struct rtc7301_priv *priv = dev_get_drvdata(rtc->dev.parent);
+	irqreturn_t ret = IRQ_NONE;
+	u8 alrm_ctrl;
+
+	spin_lock(&priv->lock);
+
+	rtc7301_select_bank(priv, 1);
+
+	alrm_ctrl = rtc7301_read(priv, RTC7301_ALARM_CONTROL);
+	if (alrm_ctrl & RTC7301_ALARM_CONTROL_AF) {
+		ret = IRQ_HANDLED;
+		rtc7301_alarm_irq(priv, false);
+		rtc_update_irq(rtc, 1, RTC_IRQF | RTC_AF);
+	}
+
+	spin_unlock(&priv->lock);
+
+	return ret;
+}
+
+static void rtc7301_init(struct rtc7301_priv *priv)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&priv->lock, flags);
+
+	rtc7301_select_bank(priv, 2);
+	rtc7301_write(priv, 0, RTC7301_TIMER_CONTROL);
+
+	spin_unlock_irqrestore(&priv->lock, flags);
+}
+
+static int __init rtc7301_rtc_probe(struct platform_device *dev)
+{
+	void __iomem *regs;
+	struct rtc7301_priv *priv;
+	struct rtc_device *rtc;
+	static const struct regmap_config *mapconf;
+	int ret;
+	u32 val;
+
+	priv = devm_kzalloc(&dev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	regs = devm_platform_ioremap_resource(dev, 0);
+	if (IS_ERR(regs))
+		return PTR_ERR(regs);
+
+	ret = device_property_read_u32(&dev->dev, "reg-io-width", &val);
+	if (ret)
+		/* Default to 32bit accesses */
+		val = 4;
+
+	switch (val) {
+	case 1:
+		mapconf = &rtc7301_regmap_8_config;
+		break;
+	case 4:
+		mapconf = &rtc7301_regmap_32_config;
+		break;
+	default:
+		dev_err(&dev->dev, "invalid reg-io-width %d\n", val);
+		return -EINVAL;
+	}
+
+	priv->regmap = devm_regmap_init_mmio(&dev->dev, regs,
+					     mapconf);
+	if (IS_ERR(priv->regmap))
+		return PTR_ERR(priv->regmap);
+
+	priv->irq = platform_get_irq(dev, 0);
+
+	spin_lock_init(&priv->lock);
+	priv->bank = -1;
+
+	rtc7301_init(priv);
+
+	platform_set_drvdata(dev, priv);
+
+	rtc = devm_rtc_device_register(&dev->dev, DRV_NAME, &rtc7301_rtc_ops,
+				       THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	if (priv->irq > 0) {
+		ret = devm_request_irq(&dev->dev, priv->irq,
+				       rtc7301_irq_handler, IRQF_SHARED,
+				       dev_name(&dev->dev), rtc);
+		if (ret) {
+			priv->irq = 0;
+			dev_err(&dev->dev, "unable to request IRQ\n");
+		} else {
+			device_set_wakeup_capable(&dev->dev, true);
+		}
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+
+static int rtc7301_suspend(struct device *dev)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(priv->irq);
+
+	return 0;
+}
+
+static int rtc7301_resume(struct device *dev)
+{
+	struct rtc7301_priv *priv = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(priv->irq);
+
+	return 0;
+}
+
+#endif
+
+static SIMPLE_DEV_PM_OPS(rtc7301_pm_ops, rtc7301_suspend, rtc7301_resume);
+
+static const struct of_device_id rtc7301_dt_match[] = {
+	{ .compatible = "epson,rtc7301sf" },
+	{ .compatible = "epson,rtc7301dg" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, rtc7301_dt_match);
+
+static struct platform_driver rtc7301_rtc_driver = {
+	.driver	= {
+		.name = DRV_NAME,
+		.of_match_table = rtc7301_dt_match,
+		.pm = &rtc7301_pm_ops,
+	},
+};
+
+module_platform_driver_probe(rtc7301_rtc_driver, rtc7301_rtc_probe);
+
+MODULE_AUTHOR("Akinobu Mita <akinobu.mita@gmail.com>");
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("EPSON TOYOCOM RTC-7301SF/DG Driver");
+MODULE_ALIAS("platform:rtc-r7301");