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, 340 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-88pm80x.c b/drivers/rtc/rtc-88pm80x.c
new file mode 100644
index 000000000..a3e52a5a7
--- /dev/null
+++ b/drivers/rtc/rtc-88pm80x.c
@@ -0,0 +1,340 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Real Time Clock driver for Marvell 88PM80x PMIC
+ *
+ * Copyright (c) 2012 Marvell International Ltd.
+ *  Wenzeng Chen<wzch@marvell.com>
+ *  Qiao Zhou <zhouqiao@marvell.com>
+ */
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/regmap.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/88pm80x.h>
+#include <linux/rtc.h>
+
+#define PM800_RTC_COUNTER1		(0xD1)
+#define PM800_RTC_COUNTER2		(0xD2)
+#define PM800_RTC_COUNTER3		(0xD3)
+#define PM800_RTC_COUNTER4		(0xD4)
+#define PM800_RTC_EXPIRE1_1		(0xD5)
+#define PM800_RTC_EXPIRE1_2		(0xD6)
+#define PM800_RTC_EXPIRE1_3		(0xD7)
+#define PM800_RTC_EXPIRE1_4		(0xD8)
+#define PM800_RTC_TRIM1			(0xD9)
+#define PM800_RTC_TRIM2			(0xDA)
+#define PM800_RTC_TRIM3			(0xDB)
+#define PM800_RTC_TRIM4			(0xDC)
+#define PM800_RTC_EXPIRE2_1		(0xDD)
+#define PM800_RTC_EXPIRE2_2		(0xDE)
+#define PM800_RTC_EXPIRE2_3		(0xDF)
+#define PM800_RTC_EXPIRE2_4		(0xE0)
+
+#define PM800_POWER_DOWN_LOG1	(0xE5)
+#define PM800_POWER_DOWN_LOG2	(0xE6)
+
+struct pm80x_rtc_info {
+	struct pm80x_chip *chip;
+	struct regmap *map;
+	struct rtc_device *rtc_dev;
+	struct device *dev;
+
+	int irq;
+};
+
+static irqreturn_t rtc_update_handler(int irq, void *data)
+{
+	struct pm80x_rtc_info *info = (struct pm80x_rtc_info *)data;
+	int mask;
+
+	mask = PM800_ALARM | PM800_ALARM_WAKEUP;
+	regmap_update_bits(info->map, PM800_RTC_CONTROL, mask | PM800_ALARM1_EN,
+			   mask);
+	rtc_update_irq(info->rtc_dev, 1, RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static int pm80x_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct pm80x_rtc_info *info = dev_get_drvdata(dev);
+
+	if (enabled)
+		regmap_update_bits(info->map, PM800_RTC_CONTROL,
+				   PM800_ALARM1_EN, PM800_ALARM1_EN);
+	else
+		regmap_update_bits(info->map, PM800_RTC_CONTROL,
+				   PM800_ALARM1_EN, 0);
+	return 0;
+}
+
+/*
+ * Calculate the next alarm time given the requested alarm time mask
+ * and the current time.
+ */
+static void rtc_next_alarm_time(struct rtc_time *next, struct rtc_time *now,
+				struct rtc_time *alrm)
+{
+	unsigned long next_time;
+	unsigned long now_time;
+
+	next->tm_year = now->tm_year;
+	next->tm_mon = now->tm_mon;
+	next->tm_mday = now->tm_mday;
+	next->tm_hour = alrm->tm_hour;
+	next->tm_min = alrm->tm_min;
+	next->tm_sec = alrm->tm_sec;
+
+	now_time = rtc_tm_to_time64(now);
+	next_time = rtc_tm_to_time64(next);
+
+	if (next_time < now_time) {
+		/* Advance one day */
+		next_time += 60 * 60 * 24;
+		rtc_time64_to_tm(next_time, next);
+	}
+}
+
+static int pm80x_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct pm80x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	unsigned long ticks, base, data;
+	regmap_raw_read(info->map, PM800_RTC_EXPIRE2_1, buf, 4);
+	base = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	dev_dbg(info->dev, "%x-%x-%x-%x\n", buf[0], buf[1], buf[2], buf[3]);
+
+	/* load 32-bit read-only counter */
+	regmap_raw_read(info->map, PM800_RTC_COUNTER1, buf, 4);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	ticks = base + data;
+	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+	rtc_time64_to_tm(ticks, tm);
+	return 0;
+}
+
+static int pm80x_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct pm80x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	unsigned long ticks, base, data;
+
+	ticks = rtc_tm_to_time64(tm);
+
+	/* load 32-bit read-only counter */
+	regmap_raw_read(info->map, PM800_RTC_COUNTER1, buf, 4);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	base = ticks - data;
+	dev_dbg(info->dev, "set base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+	buf[0] = base & 0xFF;
+	buf[1] = (base >> 8) & 0xFF;
+	buf[2] = (base >> 16) & 0xFF;
+	buf[3] = (base >> 24) & 0xFF;
+	regmap_raw_write(info->map, PM800_RTC_EXPIRE2_1, buf, 4);
+
+	return 0;
+}
+
+static int pm80x_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct pm80x_rtc_info *info = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	unsigned long ticks, base, data;
+	int ret;
+
+	regmap_raw_read(info->map, PM800_RTC_EXPIRE2_1, buf, 4);
+	base = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	dev_dbg(info->dev, "%x-%x-%x-%x\n", buf[0], buf[1], buf[2], buf[3]);
+
+	regmap_raw_read(info->map, PM800_RTC_EXPIRE1_1, buf, 4);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	ticks = base + data;
+	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+
+	rtc_time64_to_tm(ticks, &alrm->time);
+	regmap_read(info->map, PM800_RTC_CONTROL, &ret);
+	alrm->enabled = (ret & PM800_ALARM1_EN) ? 1 : 0;
+	alrm->pending = (ret & (PM800_ALARM | PM800_ALARM_WAKEUP)) ? 1 : 0;
+	return 0;
+}
+
+static int pm80x_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct pm80x_rtc_info *info = dev_get_drvdata(dev);
+	struct rtc_time now_tm, alarm_tm;
+	unsigned long ticks, base, data;
+	unsigned char buf[4];
+	int mask;
+
+	regmap_update_bits(info->map, PM800_RTC_CONTROL, PM800_ALARM1_EN, 0);
+
+	regmap_raw_read(info->map, PM800_RTC_EXPIRE2_1, buf, 4);
+	base = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	dev_dbg(info->dev, "%x-%x-%x-%x\n", buf[0], buf[1], buf[2], buf[3]);
+
+	/* load 32-bit read-only counter */
+	regmap_raw_read(info->map, PM800_RTC_COUNTER1, buf, 4);
+	data = ((unsigned long)buf[3] << 24) | (buf[2] << 16) |
+		(buf[1] << 8) | buf[0];
+	ticks = base + data;
+	dev_dbg(info->dev, "get base:0x%lx, RO count:0x%lx, ticks:0x%lx\n",
+		base, data, ticks);
+
+	rtc_time64_to_tm(ticks, &now_tm);
+	dev_dbg(info->dev, "%s, now time : %lu\n", __func__, ticks);
+	rtc_next_alarm_time(&alarm_tm, &now_tm, &alrm->time);
+	/* get new ticks for alarm in 24 hours */
+	ticks = rtc_tm_to_time64(&alarm_tm);
+	dev_dbg(info->dev, "%s, alarm time: %lu\n", __func__, ticks);
+	data = ticks - base;
+
+	buf[0] = data & 0xff;
+	buf[1] = (data >> 8) & 0xff;
+	buf[2] = (data >> 16) & 0xff;
+	buf[3] = (data >> 24) & 0xff;
+	regmap_raw_write(info->map, PM800_RTC_EXPIRE1_1, buf, 4);
+	if (alrm->enabled) {
+		mask = PM800_ALARM | PM800_ALARM_WAKEUP | PM800_ALARM1_EN;
+		regmap_update_bits(info->map, PM800_RTC_CONTROL, mask, mask);
+	} else {
+		mask = PM800_ALARM | PM800_ALARM_WAKEUP | PM800_ALARM1_EN;
+		regmap_update_bits(info->map, PM800_RTC_CONTROL, mask,
+				   PM800_ALARM | PM800_ALARM_WAKEUP);
+	}
+	return 0;
+}
+
+static const struct rtc_class_ops pm80x_rtc_ops = {
+	.read_time = pm80x_rtc_read_time,
+	.set_time = pm80x_rtc_set_time,
+	.read_alarm = pm80x_rtc_read_alarm,
+	.set_alarm = pm80x_rtc_set_alarm,
+	.alarm_irq_enable = pm80x_rtc_alarm_irq_enable,
+};
+
+#ifdef CONFIG_PM_SLEEP
+static int pm80x_rtc_suspend(struct device *dev)
+{
+	return pm80x_dev_suspend(dev);
+}
+
+static int pm80x_rtc_resume(struct device *dev)
+{
+	return pm80x_dev_resume(dev);
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(pm80x_rtc_pm_ops, pm80x_rtc_suspend, pm80x_rtc_resume);
+
+static int pm80x_rtc_probe(struct platform_device *pdev)
+{
+	struct pm80x_chip *chip = dev_get_drvdata(pdev->dev.parent);
+	struct pm80x_rtc_pdata *pdata = dev_get_platdata(&pdev->dev);
+	struct pm80x_rtc_info *info;
+	struct device_node *node = pdev->dev.of_node;
+	int ret;
+
+	if (!pdata && !node) {
+		dev_err(&pdev->dev,
+			"pm80x-rtc requires platform data or of_node\n");
+		return -EINVAL;
+	}
+
+	if (!pdata) {
+		pdata = devm_kzalloc(&pdev->dev, sizeof(*pdata), GFP_KERNEL);
+		if (!pdata) {
+			dev_err(&pdev->dev, "failed to allocate memory\n");
+			return -ENOMEM;
+		}
+	}
+
+	info =
+	    devm_kzalloc(&pdev->dev, sizeof(struct pm80x_rtc_info), GFP_KERNEL);
+	if (!info)
+		return -ENOMEM;
+	info->irq = platform_get_irq(pdev, 0);
+	if (info->irq < 0) {
+		ret = -EINVAL;
+		goto out;
+	}
+
+	info->chip = chip;
+	info->map = chip->regmap;
+	if (!info->map) {
+		dev_err(&pdev->dev, "no regmap!\n");
+		ret = -EINVAL;
+		goto out;
+	}
+
+	info->dev = &pdev->dev;
+	dev_set_drvdata(&pdev->dev, info);
+
+	info->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(info->rtc_dev))
+		return PTR_ERR(info->rtc_dev);
+
+	ret = pm80x_request_irq(chip, info->irq, rtc_update_handler,
+				IRQF_ONESHOT, "rtc", info);
+	if (ret < 0) {
+		dev_err(chip->dev, "Failed to request IRQ: #%d: %d\n",
+			info->irq, ret);
+		goto out;
+	}
+
+	info->rtc_dev->ops = &pm80x_rtc_ops;
+	info->rtc_dev->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(info->rtc_dev);
+	if (ret)
+		goto out_rtc;
+
+	/*
+	 * enable internal XO instead of internal 3.25MHz clock since it can
+	 * free running in PMIC power-down state.
+	 */
+	regmap_update_bits(info->map, PM800_RTC_CONTROL, PM800_RTC1_USE_XO,
+			   PM800_RTC1_USE_XO);
+
+	/* remember whether this power up is caused by PMIC RTC or not */
+	info->rtc_dev->dev.platform_data = &pdata->rtc_wakeup;
+
+	device_init_wakeup(&pdev->dev, true);
+
+	return 0;
+out_rtc:
+	pm80x_free_irq(chip, info->irq, info);
+out:
+	return ret;
+}
+
+static void pm80x_rtc_remove(struct platform_device *pdev)
+{
+	struct pm80x_rtc_info *info = platform_get_drvdata(pdev);
+	pm80x_free_irq(info->chip, info->irq, info);
+}
+
+static struct platform_driver pm80x_rtc_driver = {
+	.driver = {
+		   .name = "88pm80x-rtc",
+		   .pm = &pm80x_rtc_pm_ops,
+		   },
+	.probe = pm80x_rtc_probe,
+	.remove = pm80x_rtc_remove,
+};
+
+module_platform_driver(pm80x_rtc_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("Marvell 88PM80x RTC driver");
+MODULE_AUTHOR("Qiao Zhou <zhouqiao@marvell.com>");
+MODULE_ALIAS("platform:88pm80x-rtc");