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, 451 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-rc5t619.c b/drivers/rtc/rtc-rc5t619.c
new file mode 100644
index 000000000..74d169102
--- /dev/null
+++ b/drivers/rtc/rtc-rc5t619.c
@@ -0,0 +1,451 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * drivers/rtc/rtc-rc5t619.c
+ *
+ * Real time clock driver for RICOH RC5T619 power management chip.
+ *
+ * Copyright (C) 2019 Andreas Kemnade
+ */
+
+#include <linux/kernel.h>
+#include <linux/device.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/mfd/rn5t618.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/bcd.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+#include <linux/irqdomain.h>
+
+struct rc5t619_rtc {
+	int			irq;
+	struct rtc_device	*rtc;
+	struct rn5t618 *rn5t618;
+};
+
+#define CTRL1_ALARM_ENABLED 0x40
+#define CTRL1_24HR 0x20
+#define CTRL1_PERIODIC_MASK 0xf
+
+#define CTRL2_PON 0x10
+#define CTRL2_ALARM_STATUS 0x80
+#define CTRL2_CTFG 0x4
+#define CTRL2_CTC 0x1
+
+#define MONTH_CENTFLAG 0x80
+#define HOUR_PMFLAG 0x20
+#define MDAY_DAL_EXT 0x80
+
+static uint8_t rtc5t619_12hour_bcd2bin(uint8_t hour)
+{
+	if (hour & HOUR_PMFLAG) {
+		hour = bcd2bin(hour & ~HOUR_PMFLAG);
+		return hour == 12 ? 12 : 12 + hour;
+	}
+
+	hour = bcd2bin(hour);
+	return hour == 12 ? 0 : hour;
+}
+
+static uint8_t rtc5t619_12hour_bin2bcd(uint8_t hour)
+{
+	if (!hour)
+		return 0x12;
+
+	if (hour < 12)
+		return bin2bcd(hour);
+
+	if (hour == 12)
+		return 0x12 | HOUR_PMFLAG;
+
+	return bin2bcd(hour - 12) | HOUR_PMFLAG;
+}
+
+static int rc5t619_rtc_periodic_disable(struct device *dev)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	int err;
+
+	/* disable function */
+	err = regmap_update_bits(rtc->rn5t618->regmap,
+				 RN5T618_RTC_CTRL1, CTRL1_PERIODIC_MASK, 0);
+	if (err < 0)
+		return err;
+
+	/* clear alarm flag and CTFG */
+	err = regmap_update_bits(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2,
+				 CTRL2_ALARM_STATUS | CTRL2_CTFG | CTRL2_CTC,
+				 0);
+	if (err < 0)
+		return err;
+
+	return 0;
+}
+
+/* things to be done once after power on */
+static int rc5t619_rtc_pon_setup(struct device *dev)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	int err;
+	unsigned int reg_data;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2, &reg_data);
+	if (err < 0)
+		return err;
+
+	/* clear VDET PON */
+	reg_data &= ~(CTRL2_PON | CTRL2_CTC | 0x4a);	/* 0101-1011 */
+	reg_data |= 0x20;	/* 0010-0000 */
+	err = regmap_write(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2, reg_data);
+	if (err < 0)
+		return err;
+
+	/* clearing RTC Adjust register */
+	err = regmap_write(rtc->rn5t618->regmap, RN5T618_RTC_ADJUST, 0);
+	if (err)
+		return err;
+
+	return regmap_update_bits(rtc->rn5t618->regmap,
+					RN5T618_RTC_CTRL1,
+					CTRL1_24HR, CTRL1_24HR);
+}
+
+static int rc5t619_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	u8 buff[7];
+	int err;
+	int cent_flag;
+	unsigned int ctrl1;
+	unsigned int ctrl2;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2, &ctrl2);
+	if (err < 0)
+		return err;
+
+	if (ctrl2 & CTRL2_PON)
+		return -EINVAL;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL1, &ctrl1);
+	if (err < 0)
+		return err;
+
+	err = regmap_bulk_read(rtc->rn5t618->regmap, RN5T618_RTC_SECONDS,
+			       buff, sizeof(buff));
+	if (err < 0)
+		return err;
+
+	if (buff[5] & MONTH_CENTFLAG)
+		cent_flag = 1;
+	else
+		cent_flag = 0;
+
+	tm->tm_sec  = bcd2bin(buff[0]);
+	tm->tm_min  = bcd2bin(buff[1]);
+
+	if (ctrl1 & CTRL1_24HR)
+		tm->tm_hour = bcd2bin(buff[2]);
+	else
+		tm->tm_hour = rtc5t619_12hour_bcd2bin(buff[2]);
+
+	tm->tm_wday = bcd2bin(buff[3]);
+	tm->tm_mday = bcd2bin(buff[4]);
+	tm->tm_mon  = bcd2bin(buff[5] & 0x1f) - 1; /* back to system 0-11 */
+	tm->tm_year = bcd2bin(buff[6]) + 100 * cent_flag;
+
+	return 0;
+}
+
+static int rc5t619_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	u8 buff[7];
+	int err;
+	int cent_flag;
+	unsigned int ctrl1;
+	unsigned int ctrl2;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2, &ctrl2);
+	if (err < 0)
+		return err;
+
+	if (ctrl2 & CTRL2_PON)
+		rc5t619_rtc_pon_setup(dev);
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL1, &ctrl1);
+	if (err < 0)
+		return err;
+
+	if (tm->tm_year >= 100)
+		cent_flag = 1;
+	else
+		cent_flag = 0;
+
+	buff[0] = bin2bcd(tm->tm_sec);
+	buff[1] = bin2bcd(tm->tm_min);
+
+	if (ctrl1 & CTRL1_24HR)
+		buff[2] = bin2bcd(tm->tm_hour);
+	else
+		buff[2] = rtc5t619_12hour_bin2bcd(tm->tm_hour);
+
+	buff[3] = bin2bcd(tm->tm_wday);
+	buff[4] = bin2bcd(tm->tm_mday);
+	buff[5] = bin2bcd(tm->tm_mon + 1);	/* system set 0-11 */
+	buff[6] = bin2bcd(tm->tm_year - cent_flag * 100);
+
+	if (cent_flag)
+		buff[5] |= MONTH_CENTFLAG;
+
+	err = regmap_bulk_write(rtc->rn5t618->regmap, RN5T618_RTC_SECONDS,
+				buff, sizeof(buff));
+	if (err < 0) {
+		dev_err(dev, "failed to program new time: %d\n", err);
+		return err;
+	}
+
+	return 0;
+}
+
+/* 0-disable, 1-enable */
+static int rc5t619_rtc_alarm_enable(struct device *dev, unsigned int enabled)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+
+	return regmap_update_bits(rtc->rn5t618->regmap,
+			RN5T618_RTC_CTRL1,
+			CTRL1_ALARM_ENABLED,
+			enabled ? CTRL1_ALARM_ENABLED : 0);
+}
+
+static int rc5t619_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	u8 buff[6];
+	unsigned int buff_cent;
+	int err;
+	int cent_flag;
+	unsigned int ctrl1;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL1, &ctrl1);
+	if (err)
+		return err;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_MONTH, &buff_cent);
+	if (err < 0) {
+		dev_err(dev, "failed to read time: %d\n", err);
+		return err;
+	}
+
+	if (buff_cent & MONTH_CENTFLAG)
+		cent_flag = 1;
+	else
+		cent_flag = 0;
+
+	err = regmap_bulk_read(rtc->rn5t618->regmap, RN5T618_RTC_ALARM_Y_SEC,
+			       buff, sizeof(buff));
+	if (err)
+		return err;
+
+	buff[3] = buff[3] & 0x3f;
+
+	alrm->time.tm_sec  = bcd2bin(buff[0]);
+	alrm->time.tm_min  = bcd2bin(buff[1]);
+
+	if (ctrl1 & CTRL1_24HR)
+		alrm->time.tm_hour = bcd2bin(buff[2]);
+	else
+		alrm->time.tm_hour = rtc5t619_12hour_bcd2bin(buff[2]);
+
+	alrm->time.tm_mday = bcd2bin(buff[3]);
+	alrm->time.tm_mon  = bcd2bin(buff[4]) - 1;
+	alrm->time.tm_year = bcd2bin(buff[5]) + 100 * cent_flag;
+	alrm->enabled = !!(ctrl1 & CTRL1_ALARM_ENABLED);
+	dev_dbg(dev, "read alarm: %ptR\n", &alrm->time);
+
+	return 0;
+}
+
+static int rc5t619_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+	u8 buff[6];
+	int err;
+	int cent_flag;
+	unsigned int ctrl1;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL1, &ctrl1);
+	if (err)
+		return err;
+
+	err = rc5t619_rtc_alarm_enable(dev, 0);
+	if (err < 0)
+		return err;
+
+	if (rtc->irq == -1)
+		return -EINVAL;
+
+	if (alrm->enabled == 0)
+		return 0;
+
+	if (alrm->time.tm_year >= 100)
+		cent_flag = 1;
+	else
+		cent_flag = 0;
+
+	alrm->time.tm_mon += 1;
+	buff[0] = bin2bcd(alrm->time.tm_sec);
+	buff[1] = bin2bcd(alrm->time.tm_min);
+
+	if (ctrl1 & CTRL1_24HR)
+		buff[2] = bin2bcd(alrm->time.tm_hour);
+	else
+		buff[2] = rtc5t619_12hour_bin2bcd(alrm->time.tm_hour);
+
+	buff[3] = bin2bcd(alrm->time.tm_mday);
+	buff[4] = bin2bcd(alrm->time.tm_mon);
+	buff[5] = bin2bcd(alrm->time.tm_year - 100 * cent_flag);
+	buff[3] |= MDAY_DAL_EXT;
+
+	err = regmap_bulk_write(rtc->rn5t618->regmap, RN5T618_RTC_ALARM_Y_SEC,
+				buff, sizeof(buff));
+	if (err < 0)
+		return err;
+
+	return rc5t619_rtc_alarm_enable(dev, alrm->enabled);
+}
+
+static const struct rtc_class_ops rc5t619_rtc_ops = {
+	.read_time	= rc5t619_rtc_read_time,
+	.set_time	= rc5t619_rtc_set_time,
+	.set_alarm	= rc5t619_rtc_set_alarm,
+	.read_alarm	= rc5t619_rtc_read_alarm,
+	.alarm_irq_enable = rc5t619_rtc_alarm_enable,
+};
+
+static int rc5t619_rtc_alarm_flag_clr(struct device *dev)
+{
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+
+	/* clear alarm-D status bits.*/
+	return regmap_update_bits(rtc->rn5t618->regmap,
+				RN5T618_RTC_CTRL2,
+				CTRL2_ALARM_STATUS | CTRL2_CTC, 0);
+}
+
+static irqreturn_t rc5t619_rtc_irq(int irq, void *data)
+{
+	struct device *dev = data;
+	struct rc5t619_rtc *rtc = dev_get_drvdata(dev);
+
+	rc5t619_rtc_alarm_flag_clr(dev);
+
+	rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static int rc5t619_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct rn5t618 *rn5t618 = dev_get_drvdata(pdev->dev.parent);
+	struct rc5t619_rtc *rtc;
+	unsigned int ctrl2;
+	int err;
+
+	rtc = devm_kzalloc(dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->rn5t618 = rn5t618;
+
+	dev_set_drvdata(dev, rtc);
+	rtc->irq = -1;
+
+	if (rn5t618->irq_data)
+		rtc->irq = regmap_irq_get_virq(rn5t618->irq_data,
+					       RN5T618_IRQ_RTC);
+
+	if (rtc->irq  < 0)
+		rtc->irq = -1;
+
+	err = regmap_read(rtc->rn5t618->regmap, RN5T618_RTC_CTRL2, &ctrl2);
+	if (err < 0)
+		return err;
+
+	/* disable rtc periodic function */
+	err = rc5t619_rtc_periodic_disable(&pdev->dev);
+	if (err)
+		return err;
+
+	if (ctrl2 & CTRL2_PON) {
+		err = rc5t619_rtc_alarm_flag_clr(&pdev->dev);
+		if (err)
+			return err;
+	}
+
+	rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtc)) {
+		err = PTR_ERR(rtc->rtc);
+		dev_err(dev, "RTC device register: err %d\n", err);
+		return err;
+	}
+
+	rtc->rtc->ops = &rc5t619_rtc_ops;
+	rtc->rtc->range_min = RTC_TIMESTAMP_BEGIN_1900;
+	rtc->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	/* set interrupt and enable it */
+	if (rtc->irq != -1) {
+		err = devm_request_threaded_irq(&pdev->dev, rtc->irq, NULL,
+						rc5t619_rtc_irq,
+						IRQF_ONESHOT,
+						"rtc-rc5t619",
+						&pdev->dev);
+		if (err < 0) {
+			dev_err(&pdev->dev, "request IRQ:%d fail\n", rtc->irq);
+			rtc->irq = -1;
+
+			err = rc5t619_rtc_alarm_enable(&pdev->dev, 0);
+			if (err)
+				return err;
+
+		} else {
+			/* enable wake */
+			device_init_wakeup(&pdev->dev, true);
+			enable_irq_wake(rtc->irq);
+		}
+	} else {
+		/* system don't want to using alarm interrupt, so close it */
+		err = rc5t619_rtc_alarm_enable(&pdev->dev, 0);
+		if (err)
+			return err;
+
+		dev_warn(&pdev->dev, "rc5t619 interrupt is disabled\n");
+	}
+
+	return devm_rtc_register_device(rtc->rtc);
+}
+
+static const struct platform_device_id rc5t619_rtc_id[] = {
+	{
+		.name = "rc5t619-rtc",
+	}, {
+		/* sentinel */
+	}
+};
+MODULE_DEVICE_TABLE(platform, rc5t619_rtc_id);
+
+static struct platform_driver rc5t619_rtc_driver = {
+	.driver	= {
+		.name	= "rc5t619-rtc",
+	},
+	.probe	= rc5t619_rtc_probe,
+	.id_table = rc5t619_rtc_id,
+};
+module_platform_driver(rc5t619_rtc_driver);
+
+MODULE_DESCRIPTION("RICOH RC5T619 RTC driver");
+MODULE_LICENSE("GPL");