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, 474 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-wm8350.c b/drivers/rtc/rtc-wm8350.c
new file mode 100644
index 000000000..3bd60d067
--- /dev/null
+++ b/drivers/rtc/rtc-wm8350.c
@@ -0,0 +1,474 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	Real Time Clock driver for Wolfson Microelectronics WM8350
+ *
+ *	Copyright (C) 2007, 2008 Wolfson Microelectronics PLC.
+ *
+ *  Author: Liam Girdwood
+ *          linux@wolfsonmicro.com
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/time.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/interrupt.h>
+#include <linux/ioctl.h>
+#include <linux/completion.h>
+#include <linux/mfd/wm8350/rtc.h>
+#include <linux/mfd/wm8350/core.h>
+#include <linux/delay.h>
+#include <linux/platform_device.h>
+
+#define WM8350_SET_ALM_RETRIES	5
+#define WM8350_SET_TIME_RETRIES	5
+#define WM8350_GET_TIME_RETRIES	5
+
+/*
+ * Read current time and date in RTC
+ */
+static int wm8350_rtc_readtime(struct device *dev, struct rtc_time *tm)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	u16 time1[4], time2[4];
+	int retries = WM8350_GET_TIME_RETRIES, ret;
+
+	/*
+	 * Read the time twice and compare.
+	 * If time1 == time2, then time is valid else retry.
+	 */
+	do {
+		ret = wm8350_block_read(wm8350, WM8350_RTC_SECONDS_MINUTES,
+					4, time1);
+		if (ret < 0)
+			return ret;
+		ret = wm8350_block_read(wm8350, WM8350_RTC_SECONDS_MINUTES,
+					4, time2);
+		if (ret < 0)
+			return ret;
+
+		if (memcmp(time1, time2, sizeof(time1)) == 0) {
+			tm->tm_sec = time1[0] & WM8350_RTC_SECS_MASK;
+
+			tm->tm_min = (time1[0] & WM8350_RTC_MINS_MASK)
+			    >> WM8350_RTC_MINS_SHIFT;
+
+			tm->tm_hour = time1[1] & WM8350_RTC_HRS_MASK;
+
+			tm->tm_wday = ((time1[1] >> WM8350_RTC_DAY_SHIFT)
+				       & 0x7) - 1;
+
+			tm->tm_mon = ((time1[2] & WM8350_RTC_MTH_MASK)
+				      >> WM8350_RTC_MTH_SHIFT) - 1;
+
+			tm->tm_mday = (time1[2] & WM8350_RTC_DATE_MASK);
+
+			tm->tm_year = ((time1[3] & WM8350_RTC_YHUNDREDS_MASK)
+				       >> WM8350_RTC_YHUNDREDS_SHIFT) * 100;
+			tm->tm_year += time1[3] & WM8350_RTC_YUNITS_MASK;
+
+			tm->tm_yday = rtc_year_days(tm->tm_mday, tm->tm_mon,
+						    tm->tm_year);
+			tm->tm_year -= 1900;
+
+			dev_dbg(dev, "Read (%d left): %04x %04x %04x %04x\n",
+				retries,
+				time1[0], time1[1], time1[2], time1[3]);
+
+			return 0;
+		}
+	} while (retries--);
+
+	dev_err(dev, "timed out reading RTC time\n");
+	return -EIO;
+}
+
+/*
+ * Set current time and date in RTC
+ */
+static int wm8350_rtc_settime(struct device *dev, struct rtc_time *tm)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	u16 time[4];
+	u16 rtc_ctrl;
+	int ret, retries = WM8350_SET_TIME_RETRIES;
+
+	time[0] = tm->tm_sec;
+	time[0] |= tm->tm_min << WM8350_RTC_MINS_SHIFT;
+	time[1] = tm->tm_hour;
+	time[1] |= (tm->tm_wday + 1) << WM8350_RTC_DAY_SHIFT;
+	time[2] = tm->tm_mday;
+	time[2] |= (tm->tm_mon + 1) << WM8350_RTC_MTH_SHIFT;
+	time[3] = ((tm->tm_year + 1900) / 100) << WM8350_RTC_YHUNDREDS_SHIFT;
+	time[3] |= (tm->tm_year + 1900) % 100;
+
+	dev_dbg(dev, "Setting: %04x %04x %04x %04x\n",
+		time[0], time[1], time[2], time[3]);
+
+	/* Set RTC_SET to stop the clock */
+	ret = wm8350_set_bits(wm8350, WM8350_RTC_TIME_CONTROL, WM8350_RTC_SET);
+	if (ret < 0)
+		return ret;
+
+	/* Wait until confirmation of stopping */
+	do {
+		rtc_ctrl = wm8350_reg_read(wm8350, WM8350_RTC_TIME_CONTROL);
+		schedule_timeout_uninterruptible(msecs_to_jiffies(1));
+	} while (--retries && !(rtc_ctrl & WM8350_RTC_STS));
+
+	if (!retries) {
+		dev_err(dev, "timed out on set confirmation\n");
+		return -EIO;
+	}
+
+	/* Write time to RTC */
+	ret = wm8350_block_write(wm8350, WM8350_RTC_SECONDS_MINUTES, 4, time);
+	if (ret < 0)
+		return ret;
+
+	/* Clear RTC_SET to start the clock */
+	ret = wm8350_clear_bits(wm8350, WM8350_RTC_TIME_CONTROL,
+				WM8350_RTC_SET);
+	return ret;
+}
+
+/*
+ * Read alarm time and date in RTC
+ */
+static int wm8350_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	struct rtc_time *tm = &alrm->time;
+	u16 time[4];
+	int ret;
+
+	ret = wm8350_block_read(wm8350, WM8350_ALARM_SECONDS_MINUTES, 4, time);
+	if (ret < 0)
+		return ret;
+
+	tm->tm_sec = time[0] & WM8350_RTC_ALMSECS_MASK;
+	if (tm->tm_sec == WM8350_RTC_ALMSECS_MASK)
+		tm->tm_sec = -1;
+
+	tm->tm_min = time[0] & WM8350_RTC_ALMMINS_MASK;
+	if (tm->tm_min == WM8350_RTC_ALMMINS_MASK)
+		tm->tm_min = -1;
+	else
+		tm->tm_min >>= WM8350_RTC_ALMMINS_SHIFT;
+
+	tm->tm_hour = time[1] & WM8350_RTC_ALMHRS_MASK;
+	if (tm->tm_hour == WM8350_RTC_ALMHRS_MASK)
+		tm->tm_hour = -1;
+
+	tm->tm_wday = ((time[1] >> WM8350_RTC_ALMDAY_SHIFT) & 0x7) - 1;
+	if (tm->tm_wday > 7)
+		tm->tm_wday = -1;
+
+	tm->tm_mon = time[2] & WM8350_RTC_ALMMTH_MASK;
+	if (tm->tm_mon == WM8350_RTC_ALMMTH_MASK)
+		tm->tm_mon = -1;
+	else
+		tm->tm_mon = (tm->tm_mon >> WM8350_RTC_ALMMTH_SHIFT) - 1;
+
+	tm->tm_mday = (time[2] & WM8350_RTC_ALMDATE_MASK);
+	if (tm->tm_mday == WM8350_RTC_ALMDATE_MASK)
+		tm->tm_mday = -1;
+
+	tm->tm_year = -1;
+
+	alrm->enabled = !(time[3] & WM8350_RTC_ALMSTS);
+
+	return 0;
+}
+
+static int wm8350_rtc_stop_alarm(struct wm8350 *wm8350)
+{
+	int retries = WM8350_SET_ALM_RETRIES;
+	u16 rtc_ctrl;
+	int ret;
+
+	/* Set RTC_SET to stop the clock */
+	ret = wm8350_set_bits(wm8350, WM8350_RTC_TIME_CONTROL,
+			      WM8350_RTC_ALMSET);
+	if (ret < 0)
+		return ret;
+
+	/* Wait until confirmation of stopping */
+	do {
+		rtc_ctrl = wm8350_reg_read(wm8350, WM8350_RTC_TIME_CONTROL);
+		schedule_timeout_uninterruptible(msecs_to_jiffies(1));
+	} while (retries-- && !(rtc_ctrl & WM8350_RTC_ALMSTS));
+
+	if (!(rtc_ctrl & WM8350_RTC_ALMSTS))
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static int wm8350_rtc_start_alarm(struct wm8350 *wm8350)
+{
+	int ret;
+	int retries = WM8350_SET_ALM_RETRIES;
+	u16 rtc_ctrl;
+
+	ret = wm8350_clear_bits(wm8350, WM8350_RTC_TIME_CONTROL,
+				WM8350_RTC_ALMSET);
+	if (ret < 0)
+		return ret;
+
+	/* Wait until confirmation */
+	do {
+		rtc_ctrl = wm8350_reg_read(wm8350, WM8350_RTC_TIME_CONTROL);
+		schedule_timeout_uninterruptible(msecs_to_jiffies(1));
+	} while (retries-- && rtc_ctrl & WM8350_RTC_ALMSTS);
+
+	if (rtc_ctrl & WM8350_RTC_ALMSTS)
+		return -ETIMEDOUT;
+
+	return 0;
+}
+
+static int wm8350_rtc_alarm_irq_enable(struct device *dev,
+				       unsigned int enabled)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+
+	if (enabled)
+		return wm8350_rtc_start_alarm(wm8350);
+	else
+		return wm8350_rtc_stop_alarm(wm8350);
+}
+
+static int wm8350_rtc_setalarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	struct rtc_time *tm = &alrm->time;
+	u16 time[3];
+	int ret;
+
+	memset(time, 0, sizeof(time));
+
+	if (tm->tm_sec != -1)
+		time[0] |= tm->tm_sec;
+	else
+		time[0] |= WM8350_RTC_ALMSECS_MASK;
+
+	if (tm->tm_min != -1)
+		time[0] |= tm->tm_min << WM8350_RTC_ALMMINS_SHIFT;
+	else
+		time[0] |= WM8350_RTC_ALMMINS_MASK;
+
+	if (tm->tm_hour != -1)
+		time[1] |= tm->tm_hour;
+	else
+		time[1] |= WM8350_RTC_ALMHRS_MASK;
+
+	if (tm->tm_wday != -1)
+		time[1] |= (tm->tm_wday + 1) << WM8350_RTC_ALMDAY_SHIFT;
+	else
+		time[1] |= WM8350_RTC_ALMDAY_MASK;
+
+	if (tm->tm_mday != -1)
+		time[2] |= tm->tm_mday;
+	else
+		time[2] |= WM8350_RTC_ALMDATE_MASK;
+
+	if (tm->tm_mon != -1)
+		time[2] |= (tm->tm_mon + 1) << WM8350_RTC_ALMMTH_SHIFT;
+	else
+		time[2] |= WM8350_RTC_ALMMTH_MASK;
+
+	ret = wm8350_rtc_stop_alarm(wm8350);
+	if (ret < 0)
+		return ret;
+
+	/* Write time to RTC */
+	ret = wm8350_block_write(wm8350, WM8350_ALARM_SECONDS_MINUTES,
+				 3, time);
+	if (ret < 0)
+		return ret;
+
+	if (alrm->enabled)
+		ret = wm8350_rtc_start_alarm(wm8350);
+
+	return ret;
+}
+
+static irqreturn_t wm8350_rtc_alarm_handler(int irq, void *data)
+{
+	struct wm8350 *wm8350 = data;
+	struct rtc_device *rtc = wm8350->rtc.rtc;
+	int ret;
+
+	rtc_update_irq(rtc, 1, RTC_IRQF | RTC_AF);
+
+	/* Make it one shot */
+	ret = wm8350_set_bits(wm8350, WM8350_RTC_TIME_CONTROL,
+			      WM8350_RTC_ALMSET);
+	if (ret != 0) {
+		dev_err(&(wm8350->rtc.pdev->dev),
+			"Failed to disable alarm: %d\n", ret);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static irqreturn_t wm8350_rtc_update_handler(int irq, void *data)
+{
+	struct wm8350 *wm8350 = data;
+	struct rtc_device *rtc = wm8350->rtc.rtc;
+
+	rtc_update_irq(rtc, 1, RTC_IRQF | RTC_UF);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops wm8350_rtc_ops = {
+	.read_time = wm8350_rtc_readtime,
+	.set_time = wm8350_rtc_settime,
+	.read_alarm = wm8350_rtc_readalarm,
+	.set_alarm = wm8350_rtc_setalarm,
+	.alarm_irq_enable = wm8350_rtc_alarm_irq_enable,
+};
+
+#ifdef CONFIG_PM_SLEEP
+static int wm8350_rtc_suspend(struct device *dev)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	int ret = 0;
+	u16 reg;
+
+	reg = wm8350_reg_read(wm8350, WM8350_RTC_TIME_CONTROL);
+
+	if (device_may_wakeup(&wm8350->rtc.pdev->dev) &&
+	    reg & WM8350_RTC_ALMSTS) {
+		ret = wm8350_rtc_stop_alarm(wm8350);
+		if (ret != 0)
+			dev_err(dev, "Failed to stop RTC alarm: %d\n", ret);
+	}
+
+	return ret;
+}
+
+static int wm8350_rtc_resume(struct device *dev)
+{
+	struct wm8350 *wm8350 = dev_get_drvdata(dev);
+	int ret;
+
+	if (wm8350->rtc.alarm_enabled) {
+		ret = wm8350_rtc_start_alarm(wm8350);
+		if (ret != 0)
+			dev_err(dev, "Failed to restart RTC alarm: %d\n", ret);
+	}
+
+	return 0;
+}
+#endif
+
+static int wm8350_rtc_probe(struct platform_device *pdev)
+{
+	struct wm8350 *wm8350 = platform_get_drvdata(pdev);
+	struct wm8350_rtc *wm_rtc = &wm8350->rtc;
+	int ret = 0;
+	u16 timectl, power5;
+
+	timectl = wm8350_reg_read(wm8350, WM8350_RTC_TIME_CONTROL);
+	if (timectl & WM8350_RTC_BCD) {
+		dev_err(&pdev->dev, "RTC BCD mode not supported\n");
+		return -EINVAL;
+	}
+	if (timectl & WM8350_RTC_12HR) {
+		dev_err(&pdev->dev, "RTC 12 hour mode not supported\n");
+		return -EINVAL;
+	}
+
+	/* enable the RTC if it's not already enabled */
+	power5 = wm8350_reg_read(wm8350, WM8350_POWER_MGMT_5);
+	if (!(power5 &  WM8350_RTC_TICK_ENA)) {
+		wm8350_reg_unlock(wm8350);
+
+		ret = wm8350_set_bits(wm8350, WM8350_POWER_MGMT_5,
+				      WM8350_RTC_TICK_ENA);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "failed to enable RTC: %d\n", ret);
+			return ret;
+		}
+
+		wm8350_reg_lock(wm8350);
+	}
+
+	if (timectl & WM8350_RTC_STS) {
+		int retries;
+
+		ret = wm8350_clear_bits(wm8350, WM8350_RTC_TIME_CONTROL,
+					WM8350_RTC_SET);
+		if (ret < 0) {
+			dev_err(&pdev->dev, "failed to start: %d\n", ret);
+			return ret;
+		}
+
+		retries = WM8350_SET_TIME_RETRIES;
+		do {
+			timectl = wm8350_reg_read(wm8350,
+						  WM8350_RTC_TIME_CONTROL);
+		} while (timectl & WM8350_RTC_STS && --retries);
+
+		if (retries == 0) {
+			dev_err(&pdev->dev, "failed to start: timeout\n");
+			return -ENODEV;
+		}
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	wm_rtc->rtc = devm_rtc_device_register(&pdev->dev, "wm8350",
+					&wm8350_rtc_ops, THIS_MODULE);
+	if (IS_ERR(wm_rtc->rtc))
+		return PTR_ERR(wm_rtc->rtc);
+
+	ret = wm8350_register_irq(wm8350, WM8350_IRQ_RTC_SEC,
+			    wm8350_rtc_update_handler, 0,
+			    "RTC Seconds", wm8350);
+	if (ret)
+		return ret;
+
+	wm8350_mask_irq(wm8350, WM8350_IRQ_RTC_SEC);
+
+	ret = wm8350_register_irq(wm8350, WM8350_IRQ_RTC_ALM,
+			    wm8350_rtc_alarm_handler, 0,
+			    "RTC Alarm", wm8350);
+	if (ret) {
+		wm8350_free_irq(wm8350, WM8350_IRQ_RTC_SEC, wm8350);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void wm8350_rtc_remove(struct platform_device *pdev)
+{
+	struct wm8350 *wm8350 = platform_get_drvdata(pdev);
+
+	wm8350_free_irq(wm8350, WM8350_IRQ_RTC_SEC, wm8350);
+	wm8350_free_irq(wm8350, WM8350_IRQ_RTC_ALM, wm8350);
+}
+
+static SIMPLE_DEV_PM_OPS(wm8350_rtc_pm_ops, wm8350_rtc_suspend,
+			wm8350_rtc_resume);
+
+static struct platform_driver wm8350_rtc_driver = {
+	.probe = wm8350_rtc_probe,
+	.remove = wm8350_rtc_remove,
+	.driver = {
+		.name = "wm8350-rtc",
+		.pm = &wm8350_rtc_pm_ops,
+	},
+};
+
+module_platform_driver(wm8350_rtc_driver);
+
+MODULE_AUTHOR("Mark Brown <broonie@opensource.wolfsonmicro.com>");
+MODULE_DESCRIPTION("RTC driver for the WM8350");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:wm8350-rtc");