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, 584 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1374.c b/drivers/rtc/rtc-ds1374.c
new file mode 100644
index 000000000..8c247215d
--- /dev/null
+++ b/drivers/rtc/rtc-ds1374.c
@@ -0,0 +1,584 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * RTC client/driver for the Maxim/Dallas DS1374 Real-Time Clock over I2C
+ *
+ * Based on code by Randy Vinson <rvinson@mvista.com>,
+ * which was based on the m41t00.c by Mark Greer <mgreer@mvista.com>.
+ *
+ * Copyright (C) 2014 Rose Technology
+ * Copyright (C) 2006-2007 Freescale Semiconductor
+ * Copyright (c) 2005 MontaVista Software, Inc.
+ */
+/*
+ * It would be more efficient to use i2c msgs/i2c_transfer directly but, as
+ * recommended in .../Documentation/i2c/writing-clients.rst section
+ * "Sending and receiving", using SMBus level communication is preferred.
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/i2c.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/workqueue.h>
+#include <linux/slab.h>
+#include <linux/pm.h>
+#ifdef CONFIG_RTC_DRV_DS1374_WDT
+#include <linux/fs.h>
+#include <linux/ioctl.h>
+#include <linux/miscdevice.h>
+#include <linux/reboot.h>
+#include <linux/watchdog.h>
+#endif
+
+#define DS1374_REG_TOD0		0x00 /* Time of Day */
+#define DS1374_REG_TOD1		0x01
+#define DS1374_REG_TOD2		0x02
+#define DS1374_REG_TOD3		0x03
+#define DS1374_REG_WDALM0	0x04 /* Watchdog/Alarm */
+#define DS1374_REG_WDALM1	0x05
+#define DS1374_REG_WDALM2	0x06
+#define DS1374_REG_CR		0x07 /* Control */
+#define DS1374_REG_CR_AIE	0x01 /* Alarm Int. Enable */
+#define DS1374_REG_CR_WDSTR	0x08 /* 1=INT, 0=RST */
+#define DS1374_REG_CR_WDALM	0x20 /* 1=Watchdog, 0=Alarm */
+#define DS1374_REG_CR_WACE	0x40 /* WD/Alarm counter enable */
+#define DS1374_REG_SR		0x08 /* Status */
+#define DS1374_REG_SR_OSF	0x80 /* Oscillator Stop Flag */
+#define DS1374_REG_SR_AF	0x01 /* Alarm Flag */
+#define DS1374_REG_TCR		0x09 /* Trickle Charge */
+
+static const struct i2c_device_id ds1374_id[] = {
+	{ .name = "ds1374" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, ds1374_id);
+
+#ifdef CONFIG_OF
+static const struct of_device_id ds1374_of_match[] = {
+	{ .compatible = "dallas,ds1374" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, ds1374_of_match);
+#endif
+
+struct ds1374 {
+	struct i2c_client *client;
+	struct rtc_device *rtc;
+	struct work_struct work;
+#ifdef CONFIG_RTC_DRV_DS1374_WDT
+	struct watchdog_device wdt;
+#endif
+	/* The mutex protects alarm operations, and prevents a race
+	 * between the enable_irq() in the workqueue and the free_irq()
+	 * in the remove function.
+	 */
+	struct mutex mutex;
+	int exiting;
+};
+
+static struct i2c_driver ds1374_driver;
+
+static int ds1374_read_rtc(struct i2c_client *client, u32 *time,
+			   int reg, int nbytes)
+{
+	u8 buf[4];
+	int ret;
+	int i;
+
+	if (WARN_ON(nbytes > 4))
+		return -EINVAL;
+
+	ret = i2c_smbus_read_i2c_block_data(client, reg, nbytes, buf);
+
+	if (ret < 0)
+		return ret;
+	if (ret < nbytes)
+		return -EIO;
+
+	for (i = nbytes - 1, *time = 0; i >= 0; i--)
+		*time = (*time << 8) | buf[i];
+
+	return 0;
+}
+
+static int ds1374_write_rtc(struct i2c_client *client, u32 time,
+			    int reg, int nbytes)
+{
+	u8 buf[4];
+	int i;
+
+	if (nbytes > 4) {
+		WARN_ON(1);
+		return -EINVAL;
+	}
+
+	for (i = 0; i < nbytes; i++) {
+		buf[i] = time & 0xff;
+		time >>= 8;
+	}
+
+	return i2c_smbus_write_i2c_block_data(client, reg, nbytes, buf);
+}
+
+static int ds1374_check_rtc_status(struct i2c_client *client)
+{
+	int ret = 0;
+	int control, stat;
+
+	stat = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
+	if (stat < 0)
+		return stat;
+
+	if (stat & DS1374_REG_SR_OSF)
+		dev_warn(&client->dev,
+			 "oscillator discontinuity flagged, time unreliable\n");
+
+	stat &= ~(DS1374_REG_SR_OSF | DS1374_REG_SR_AF);
+
+	ret = i2c_smbus_write_byte_data(client, DS1374_REG_SR, stat);
+	if (ret < 0)
+		return ret;
+
+	/* If the alarm is pending, clear it before requesting
+	 * the interrupt, so an interrupt event isn't reported
+	 * before everything is initialized.
+	 */
+
+	control = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (control < 0)
+		return control;
+
+	control &= ~(DS1374_REG_CR_WACE | DS1374_REG_CR_AIE);
+	return i2c_smbus_write_byte_data(client, DS1374_REG_CR, control);
+}
+
+static int ds1374_read_time(struct device *dev, struct rtc_time *time)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	u32 itime;
+	int ret;
+
+	ret = ds1374_read_rtc(client, &itime, DS1374_REG_TOD0, 4);
+	if (!ret)
+		rtc_time64_to_tm(itime, time);
+
+	return ret;
+}
+
+static int ds1374_set_time(struct device *dev, struct rtc_time *time)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned long itime = rtc_tm_to_time64(time);
+
+	return ds1374_write_rtc(client, itime, DS1374_REG_TOD0, 4);
+}
+
+#ifndef CONFIG_RTC_DRV_DS1374_WDT
+/* The ds1374 has a decrementer for an alarm, rather than a comparator.
+ * If the time of day is changed, then the alarm will need to be
+ * reset.
+ */
+static int ds1374_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct ds1374 *ds1374 = i2c_get_clientdata(client);
+	u32 now, cur_alarm;
+	int cr, sr;
+	int ret = 0;
+
+	if (client->irq <= 0)
+		return -EINVAL;
+
+	mutex_lock(&ds1374->mutex);
+
+	cr = ret = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (ret < 0)
+		goto out;
+
+	sr = ret = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
+	if (ret < 0)
+		goto out;
+
+	ret = ds1374_read_rtc(client, &now, DS1374_REG_TOD0, 4);
+	if (ret)
+		goto out;
+
+	ret = ds1374_read_rtc(client, &cur_alarm, DS1374_REG_WDALM0, 3);
+	if (ret)
+		goto out;
+
+	rtc_time64_to_tm(now + cur_alarm, &alarm->time);
+	alarm->enabled = !!(cr & DS1374_REG_CR_WACE);
+	alarm->pending = !!(sr & DS1374_REG_SR_AF);
+
+out:
+	mutex_unlock(&ds1374->mutex);
+	return ret;
+}
+
+static int ds1374_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct ds1374 *ds1374 = i2c_get_clientdata(client);
+	struct rtc_time now;
+	unsigned long new_alarm, itime;
+	int cr;
+	int ret = 0;
+
+	if (client->irq <= 0)
+		return -EINVAL;
+
+	ret = ds1374_read_time(dev, &now);
+	if (ret < 0)
+		return ret;
+
+	new_alarm = rtc_tm_to_time64(&alarm->time);
+	itime = rtc_tm_to_time64(&now);
+
+	/* This can happen due to races, in addition to dates that are
+	 * truly in the past.  To avoid requiring the caller to check for
+	 * races, dates in the past are assumed to be in the recent past
+	 * (i.e. not something that we'd rather the caller know about via
+	 * an error), and the alarm is set to go off as soon as possible.
+	 */
+	if (time_before_eq(new_alarm, itime))
+		new_alarm = 1;
+	else
+		new_alarm -= itime;
+
+	mutex_lock(&ds1374->mutex);
+
+	ret = cr = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (ret < 0)
+		goto out;
+
+	/* Disable any existing alarm before setting the new one
+	 * (or lack thereof). */
+	cr &= ~DS1374_REG_CR_WACE;
+
+	ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
+	if (ret < 0)
+		goto out;
+
+	ret = ds1374_write_rtc(client, new_alarm, DS1374_REG_WDALM0, 3);
+	if (ret)
+		goto out;
+
+	if (alarm->enabled) {
+		cr |= DS1374_REG_CR_WACE | DS1374_REG_CR_AIE;
+		cr &= ~DS1374_REG_CR_WDALM;
+
+		ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
+	}
+
+out:
+	mutex_unlock(&ds1374->mutex);
+	return ret;
+}
+#endif
+
+static irqreturn_t ds1374_irq(int irq, void *dev_id)
+{
+	struct i2c_client *client = dev_id;
+	struct ds1374 *ds1374 = i2c_get_clientdata(client);
+
+	disable_irq_nosync(irq);
+	schedule_work(&ds1374->work);
+	return IRQ_HANDLED;
+}
+
+static void ds1374_work(struct work_struct *work)
+{
+	struct ds1374 *ds1374 = container_of(work, struct ds1374, work);
+	struct i2c_client *client = ds1374->client;
+	int stat, control;
+
+	mutex_lock(&ds1374->mutex);
+
+	stat = i2c_smbus_read_byte_data(client, DS1374_REG_SR);
+	if (stat < 0)
+		goto unlock;
+
+	if (stat & DS1374_REG_SR_AF) {
+		stat &= ~DS1374_REG_SR_AF;
+		i2c_smbus_write_byte_data(client, DS1374_REG_SR, stat);
+
+		control = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+		if (control < 0)
+			goto out;
+
+		control &= ~(DS1374_REG_CR_WACE | DS1374_REG_CR_AIE);
+		i2c_smbus_write_byte_data(client, DS1374_REG_CR, control);
+
+		rtc_update_irq(ds1374->rtc, 1, RTC_AF | RTC_IRQF);
+	}
+
+out:
+	if (!ds1374->exiting)
+		enable_irq(client->irq);
+unlock:
+	mutex_unlock(&ds1374->mutex);
+}
+
+#ifndef CONFIG_RTC_DRV_DS1374_WDT
+static int ds1374_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct ds1374 *ds1374 = i2c_get_clientdata(client);
+	int ret;
+
+	mutex_lock(&ds1374->mutex);
+
+	ret = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (ret < 0)
+		goto out;
+
+	if (enabled) {
+		ret |= DS1374_REG_CR_WACE | DS1374_REG_CR_AIE;
+		ret &= ~DS1374_REG_CR_WDALM;
+	} else {
+		ret &= ~DS1374_REG_CR_WACE;
+	}
+	ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, ret);
+
+out:
+	mutex_unlock(&ds1374->mutex);
+	return ret;
+}
+#endif
+
+static const struct rtc_class_ops ds1374_rtc_ops = {
+	.read_time = ds1374_read_time,
+	.set_time = ds1374_set_time,
+#ifndef CONFIG_RTC_DRV_DS1374_WDT
+	.read_alarm = ds1374_read_alarm,
+	.set_alarm = ds1374_set_alarm,
+	.alarm_irq_enable = ds1374_alarm_irq_enable,
+#endif
+};
+
+#ifdef CONFIG_RTC_DRV_DS1374_WDT
+/*
+ *****************************************************************************
+ *
+ * Watchdog Driver
+ *
+ *****************************************************************************
+ */
+/* Default margin */
+#define TIMER_MARGIN_DEFAULT	32
+#define TIMER_MARGIN_MIN	1
+#define TIMER_MARGIN_MAX	4095 /* 24-bit value */
+
+static int wdt_margin;
+module_param(wdt_margin, int, 0);
+MODULE_PARM_DESC(wdt_margin, "Watchdog timeout in seconds (default 32s)");
+
+static bool nowayout = WATCHDOG_NOWAYOUT;
+module_param(nowayout, bool, 0);
+MODULE_PARM_DESC(nowayout, "Watchdog cannot be stopped once started (default ="
+		__MODULE_STRING(WATCHDOG_NOWAYOUT)")");
+
+static const struct watchdog_info ds1374_wdt_info = {
+	.identity       = "DS1374 Watchdog",
+	.options        = WDIOF_SETTIMEOUT | WDIOF_KEEPALIVEPING |
+						WDIOF_MAGICCLOSE,
+};
+
+static int ds1374_wdt_settimeout(struct watchdog_device *wdt, unsigned int timeout)
+{
+	struct ds1374 *ds1374 = watchdog_get_drvdata(wdt);
+	struct i2c_client *client = ds1374->client;
+	int ret, cr;
+
+	wdt->timeout = timeout;
+
+	cr = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (cr < 0)
+		return cr;
+
+	/* Disable any existing watchdog/alarm before setting the new one */
+	cr &= ~DS1374_REG_CR_WACE;
+
+	ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
+	if (ret < 0)
+		return ret;
+
+	/* Set new watchdog time */
+	timeout = timeout * 4096;
+	ret = ds1374_write_rtc(client, timeout, DS1374_REG_WDALM0, 3);
+	if (ret)
+		return ret;
+
+	/* Enable watchdog timer */
+	cr |= DS1374_REG_CR_WACE | DS1374_REG_CR_WDALM;
+	cr &= ~DS1374_REG_CR_WDSTR;/* for RST PIN */
+	cr &= ~DS1374_REG_CR_AIE;
+
+	ret = i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+/*
+ * Reload the watchdog timer.  (ie, pat the watchdog)
+ */
+static int ds1374_wdt_start(struct watchdog_device *wdt)
+{
+	struct ds1374 *ds1374 = watchdog_get_drvdata(wdt);
+	u32 val;
+
+	return ds1374_read_rtc(ds1374->client, &val, DS1374_REG_WDALM0, 3);
+}
+
+static int ds1374_wdt_stop(struct watchdog_device *wdt)
+{
+	struct ds1374 *ds1374 = watchdog_get_drvdata(wdt);
+	struct i2c_client *client = ds1374->client;
+	int cr;
+
+	cr = i2c_smbus_read_byte_data(client, DS1374_REG_CR);
+	if (cr < 0)
+		return cr;
+
+	/* Disable watchdog timer */
+	cr &= ~DS1374_REG_CR_WACE;
+
+	return i2c_smbus_write_byte_data(client, DS1374_REG_CR, cr);
+}
+
+static const struct watchdog_ops ds1374_wdt_ops = {
+	.owner          = THIS_MODULE,
+	.start          = ds1374_wdt_start,
+	.stop           = ds1374_wdt_stop,
+	.set_timeout    = ds1374_wdt_settimeout,
+};
+#endif /*CONFIG_RTC_DRV_DS1374_WDT*/
+/*
+ *****************************************************************************
+ *
+ *	Driver Interface
+ *
+ *****************************************************************************
+ */
+static int ds1374_probe(struct i2c_client *client)
+{
+	struct ds1374 *ds1374;
+	int ret;
+
+	ds1374 = devm_kzalloc(&client->dev, sizeof(struct ds1374), GFP_KERNEL);
+	if (!ds1374)
+		return -ENOMEM;
+
+	ds1374->rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(ds1374->rtc))
+		return PTR_ERR(ds1374->rtc);
+
+	ds1374->client = client;
+	i2c_set_clientdata(client, ds1374);
+
+	INIT_WORK(&ds1374->work, ds1374_work);
+	mutex_init(&ds1374->mutex);
+
+	ret = ds1374_check_rtc_status(client);
+	if (ret)
+		return ret;
+
+	if (client->irq > 0) {
+		ret = devm_request_irq(&client->dev, client->irq, ds1374_irq, 0,
+					"ds1374", client);
+		if (ret) {
+			dev_err(&client->dev, "unable to request IRQ\n");
+			return ret;
+		}
+
+		device_set_wakeup_capable(&client->dev, 1);
+	}
+
+	ds1374->rtc->ops = &ds1374_rtc_ops;
+	ds1374->rtc->range_max = U32_MAX;
+
+	ret = devm_rtc_register_device(ds1374->rtc);
+	if (ret)
+		return ret;
+
+#ifdef CONFIG_RTC_DRV_DS1374_WDT
+	ds1374->wdt.info = &ds1374_wdt_info;
+	ds1374->wdt.ops = &ds1374_wdt_ops;
+	ds1374->wdt.timeout = TIMER_MARGIN_DEFAULT;
+	ds1374->wdt.min_timeout = TIMER_MARGIN_MIN;
+	ds1374->wdt.max_timeout = TIMER_MARGIN_MAX;
+
+	watchdog_init_timeout(&ds1374->wdt, wdt_margin, &client->dev);
+	watchdog_set_nowayout(&ds1374->wdt, nowayout);
+	watchdog_stop_on_reboot(&ds1374->wdt);
+	watchdog_stop_on_unregister(&ds1374->wdt);
+	watchdog_set_drvdata(&ds1374->wdt, ds1374);
+	ds1374_wdt_settimeout(&ds1374->wdt, ds1374->wdt.timeout);
+
+	ret = devm_watchdog_register_device(&client->dev, &ds1374->wdt);
+	if (ret)
+		return ret;
+#endif
+
+	return 0;
+}
+
+static void ds1374_remove(struct i2c_client *client)
+{
+	struct ds1374 *ds1374 = i2c_get_clientdata(client);
+
+	if (client->irq > 0) {
+		mutex_lock(&ds1374->mutex);
+		ds1374->exiting = 1;
+		mutex_unlock(&ds1374->mutex);
+
+		devm_free_irq(&client->dev, client->irq, client);
+		cancel_work_sync(&ds1374->work);
+	}
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int ds1374_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	if (client->irq > 0 && device_may_wakeup(&client->dev))
+		enable_irq_wake(client->irq);
+	return 0;
+}
+
+static int ds1374_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	if (client->irq > 0 && device_may_wakeup(&client->dev))
+		disable_irq_wake(client->irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(ds1374_pm, ds1374_suspend, ds1374_resume);
+
+static struct i2c_driver ds1374_driver = {
+	.driver = {
+		.name = "rtc-ds1374",
+		.of_match_table = of_match_ptr(ds1374_of_match),
+		.pm = &ds1374_pm,
+	},
+	.probe = ds1374_probe,
+	.remove = ds1374_remove,
+	.id_table = ds1374_id,
+};
+
+module_i2c_driver(ds1374_driver);
+
+MODULE_AUTHOR("Scott Wood <scottwood@freescale.com>");
+MODULE_DESCRIPTION("Maxim/Dallas DS1374 RTC Driver");
+MODULE_LICENSE("GPL");