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, 434 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-rx8010.c b/drivers/rtc/rtc-rx8010.c
new file mode 100644
index 000000000..ce3954132
--- /dev/null
+++ b/drivers/rtc/rtc-rx8010.c
@@ -0,0 +1,434 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for the Epson RTC module RX-8010 SJ
+ *
+ * Copyright(C) Timesys Corporation 2015
+ * Copyright(C) General Electric Company 2015
+ */
+
+#include <linux/bcd.h>
+#include <linux/bitops.h>
+#include <linux/i2c.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+
+#define RX8010_SEC		0x10
+#define RX8010_MIN		0x11
+#define RX8010_HOUR		0x12
+#define RX8010_WDAY		0x13
+#define RX8010_MDAY		0x14
+#define RX8010_MONTH		0x15
+#define RX8010_YEAR		0x16
+#define RX8010_RESV17		0x17
+#define RX8010_ALMIN		0x18
+#define RX8010_ALHOUR		0x19
+#define RX8010_ALWDAY		0x1A
+#define RX8010_TCOUNT0		0x1B
+#define RX8010_TCOUNT1		0x1C
+#define RX8010_EXT		0x1D
+#define RX8010_FLAG		0x1E
+#define RX8010_CTRL		0x1F
+/* 0x20 to 0x2F are user registers */
+#define RX8010_RESV30		0x30
+#define RX8010_RESV31		0x31
+#define RX8010_IRQ		0x32
+
+#define RX8010_EXT_WADA		BIT(3)
+
+#define RX8010_FLAG_VLF		BIT(1)
+#define RX8010_FLAG_AF		BIT(3)
+#define RX8010_FLAG_TF		BIT(4)
+#define RX8010_FLAG_UF		BIT(5)
+
+#define RX8010_CTRL_AIE		BIT(3)
+#define RX8010_CTRL_UIE		BIT(5)
+#define RX8010_CTRL_STOP	BIT(6)
+#define RX8010_CTRL_TEST	BIT(7)
+
+#define RX8010_ALARM_AE		BIT(7)
+
+static const struct i2c_device_id rx8010_id[] = {
+	{ .name = "rx8010" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, rx8010_id);
+
+static const __maybe_unused struct of_device_id rx8010_of_match[] = {
+	{ .compatible = "epson,rx8010" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, rx8010_of_match);
+
+struct rx8010_data {
+	struct regmap *regs;
+	struct rtc_device *rtc;
+	u8 ctrlreg;
+};
+
+static irqreturn_t rx8010_irq_1_handler(int irq, void *dev_id)
+{
+	struct i2c_client *client = dev_id;
+	struct rx8010_data *rx8010 = i2c_get_clientdata(client);
+	int flagreg, err;
+
+	rtc_lock(rx8010->rtc);
+
+	err = regmap_read(rx8010->regs, RX8010_FLAG, &flagreg);
+	if (err) {
+		rtc_unlock(rx8010->rtc);
+		return IRQ_NONE;
+	}
+
+	if (flagreg & RX8010_FLAG_VLF)
+		dev_warn(&client->dev, "Frequency stop detected\n");
+
+	if (flagreg & RX8010_FLAG_TF) {
+		flagreg &= ~RX8010_FLAG_TF;
+		rtc_update_irq(rx8010->rtc, 1, RTC_PF | RTC_IRQF);
+	}
+
+	if (flagreg & RX8010_FLAG_AF) {
+		flagreg &= ~RX8010_FLAG_AF;
+		rtc_update_irq(rx8010->rtc, 1, RTC_AF | RTC_IRQF);
+	}
+
+	if (flagreg & RX8010_FLAG_UF) {
+		flagreg &= ~RX8010_FLAG_UF;
+		rtc_update_irq(rx8010->rtc, 1, RTC_UF | RTC_IRQF);
+	}
+
+	err = regmap_write(rx8010->regs, RX8010_FLAG, flagreg);
+	rtc_unlock(rx8010->rtc);
+	return err ? IRQ_NONE : IRQ_HANDLED;
+}
+
+static int rx8010_get_time(struct device *dev, struct rtc_time *dt)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	u8 date[RX8010_YEAR - RX8010_SEC + 1];
+	int flagreg, err;
+
+	err = regmap_read(rx8010->regs, RX8010_FLAG, &flagreg);
+	if (err)
+		return err;
+
+	if (flagreg & RX8010_FLAG_VLF) {
+		dev_warn(dev, "Frequency stop detected\n");
+		return -EINVAL;
+	}
+
+	err = regmap_bulk_read(rx8010->regs, RX8010_SEC, date, sizeof(date));
+	if (err)
+		return err;
+
+	dt->tm_sec = bcd2bin(date[RX8010_SEC - RX8010_SEC] & 0x7f);
+	dt->tm_min = bcd2bin(date[RX8010_MIN - RX8010_SEC] & 0x7f);
+	dt->tm_hour = bcd2bin(date[RX8010_HOUR - RX8010_SEC] & 0x3f);
+	dt->tm_mday = bcd2bin(date[RX8010_MDAY - RX8010_SEC] & 0x3f);
+	dt->tm_mon = bcd2bin(date[RX8010_MONTH - RX8010_SEC] & 0x1f) - 1;
+	dt->tm_year = bcd2bin(date[RX8010_YEAR - RX8010_SEC]) + 100;
+	dt->tm_wday = ffs(date[RX8010_WDAY - RX8010_SEC] & 0x7f);
+
+	return 0;
+}
+
+static int rx8010_set_time(struct device *dev, struct rtc_time *dt)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	u8 date[RX8010_YEAR - RX8010_SEC + 1];
+	int err;
+
+	/* set STOP bit before changing clock/calendar */
+	err = regmap_set_bits(rx8010->regs, RX8010_CTRL, RX8010_CTRL_STOP);
+	if (err)
+		return err;
+
+	date[RX8010_SEC - RX8010_SEC] = bin2bcd(dt->tm_sec);
+	date[RX8010_MIN - RX8010_SEC] = bin2bcd(dt->tm_min);
+	date[RX8010_HOUR - RX8010_SEC] = bin2bcd(dt->tm_hour);
+	date[RX8010_MDAY - RX8010_SEC] = bin2bcd(dt->tm_mday);
+	date[RX8010_MONTH - RX8010_SEC] = bin2bcd(dt->tm_mon + 1);
+	date[RX8010_YEAR - RX8010_SEC] = bin2bcd(dt->tm_year - 100);
+	date[RX8010_WDAY - RX8010_SEC] = bin2bcd(1 << dt->tm_wday);
+
+	err = regmap_bulk_write(rx8010->regs, RX8010_SEC, date, sizeof(date));
+	if (err)
+		return err;
+
+	/* clear STOP bit after changing clock/calendar */
+	err = regmap_clear_bits(rx8010->regs, RX8010_CTRL, RX8010_CTRL_STOP);
+	if (err)
+		return err;
+
+	err = regmap_clear_bits(rx8010->regs, RX8010_FLAG, RX8010_FLAG_VLF);
+	if (err)
+		return err;
+
+	return 0;
+}
+
+static int rx8010_init(struct device *dev)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	u8 ctrl[2];
+	int need_clear = 0, err;
+
+	/* Initialize reserved registers as specified in datasheet */
+	err = regmap_write(rx8010->regs, RX8010_RESV17, 0xD8);
+	if (err)
+		return err;
+
+	err = regmap_write(rx8010->regs, RX8010_RESV30, 0x00);
+	if (err)
+		return err;
+
+	err = regmap_write(rx8010->regs, RX8010_RESV31, 0x08);
+	if (err)
+		return err;
+
+	err = regmap_write(rx8010->regs, RX8010_IRQ, 0x00);
+	if (err)
+		return err;
+
+	err = regmap_bulk_read(rx8010->regs, RX8010_FLAG, ctrl, 2);
+	if (err)
+		return err;
+
+	if (ctrl[0] & RX8010_FLAG_VLF)
+		dev_warn(dev, "Frequency stop was detected\n");
+
+	if (ctrl[0] & RX8010_FLAG_AF) {
+		dev_warn(dev, "Alarm was detected\n");
+		need_clear = 1;
+	}
+
+	if (ctrl[0] & RX8010_FLAG_TF)
+		need_clear = 1;
+
+	if (ctrl[0] & RX8010_FLAG_UF)
+		need_clear = 1;
+
+	if (need_clear) {
+		ctrl[0] &= ~(RX8010_FLAG_AF | RX8010_FLAG_TF | RX8010_FLAG_UF);
+		err = regmap_write(rx8010->regs, RX8010_FLAG, ctrl[0]);
+		if (err)
+			return err;
+	}
+
+	rx8010->ctrlreg = (ctrl[1] & ~RX8010_CTRL_TEST);
+
+	return 0;
+}
+
+static int rx8010_read_alarm(struct device *dev, struct rtc_wkalrm *t)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	u8 alarmvals[3];
+	int flagreg, err;
+
+	err = regmap_bulk_read(rx8010->regs, RX8010_ALMIN, alarmvals, 3);
+	if (err)
+		return err;
+
+	err = regmap_read(rx8010->regs, RX8010_FLAG, &flagreg);
+	if (err)
+		return err;
+
+	t->time.tm_sec = 0;
+	t->time.tm_min = bcd2bin(alarmvals[0] & 0x7f);
+	t->time.tm_hour = bcd2bin(alarmvals[1] & 0x3f);
+
+	if (!(alarmvals[2] & RX8010_ALARM_AE))
+		t->time.tm_mday = bcd2bin(alarmvals[2] & 0x7f);
+
+	t->enabled = !!(rx8010->ctrlreg & RX8010_CTRL_AIE);
+	t->pending = (flagreg & RX8010_FLAG_AF) && t->enabled;
+
+	return 0;
+}
+
+static int rx8010_set_alarm(struct device *dev, struct rtc_wkalrm *t)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	u8 alarmvals[3];
+	int err;
+
+	if (rx8010->ctrlreg & (RX8010_CTRL_AIE | RX8010_CTRL_UIE)) {
+		rx8010->ctrlreg &= ~(RX8010_CTRL_AIE | RX8010_CTRL_UIE);
+		err = regmap_write(rx8010->regs, RX8010_CTRL, rx8010->ctrlreg);
+		if (err)
+			return err;
+	}
+
+	err = regmap_clear_bits(rx8010->regs, RX8010_FLAG, RX8010_FLAG_AF);
+	if (err)
+		return err;
+
+	alarmvals[0] = bin2bcd(t->time.tm_min);
+	alarmvals[1] = bin2bcd(t->time.tm_hour);
+	alarmvals[2] = bin2bcd(t->time.tm_mday);
+
+	err = regmap_bulk_write(rx8010->regs, RX8010_ALMIN, alarmvals, 2);
+	if (err)
+		return err;
+
+	err = regmap_clear_bits(rx8010->regs, RX8010_EXT, RX8010_EXT_WADA);
+	if (err)
+		return err;
+
+	if (alarmvals[2] == 0)
+		alarmvals[2] |= RX8010_ALARM_AE;
+
+	err = regmap_write(rx8010->regs, RX8010_ALWDAY, alarmvals[2]);
+	if (err)
+		return err;
+
+	if (t->enabled) {
+		if (rx8010->rtc->uie_rtctimer.enabled)
+			rx8010->ctrlreg |= RX8010_CTRL_UIE;
+		if (rx8010->rtc->aie_timer.enabled)
+			rx8010->ctrlreg |=
+				(RX8010_CTRL_AIE | RX8010_CTRL_UIE);
+
+		err = regmap_write(rx8010->regs, RX8010_CTRL, rx8010->ctrlreg);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static int rx8010_alarm_irq_enable(struct device *dev,
+				   unsigned int enabled)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	int err;
+	u8 ctrl;
+
+	ctrl = rx8010->ctrlreg;
+
+	if (enabled) {
+		if (rx8010->rtc->uie_rtctimer.enabled)
+			ctrl |= RX8010_CTRL_UIE;
+		if (rx8010->rtc->aie_timer.enabled)
+			ctrl |= (RX8010_CTRL_AIE | RX8010_CTRL_UIE);
+	} else {
+		if (!rx8010->rtc->uie_rtctimer.enabled)
+			ctrl &= ~RX8010_CTRL_UIE;
+		if (!rx8010->rtc->aie_timer.enabled)
+			ctrl &= ~RX8010_CTRL_AIE;
+	}
+
+	err = regmap_clear_bits(rx8010->regs, RX8010_FLAG, RX8010_FLAG_AF);
+	if (err)
+		return err;
+
+	if (ctrl != rx8010->ctrlreg) {
+		rx8010->ctrlreg = ctrl;
+		err = regmap_write(rx8010->regs, RX8010_CTRL, rx8010->ctrlreg);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
+static int rx8010_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+	struct rx8010_data *rx8010 = dev_get_drvdata(dev);
+	int tmp, flagreg, err;
+
+	switch (cmd) {
+	case RTC_VL_READ:
+		err = regmap_read(rx8010->regs, RX8010_FLAG, &flagreg);
+		if (err)
+			return err;
+
+		tmp = flagreg & RX8010_FLAG_VLF ? RTC_VL_DATA_INVALID : 0;
+		return put_user(tmp, (unsigned int __user *)arg);
+
+	default:
+		return -ENOIOCTLCMD;
+	}
+}
+
+static const struct rtc_class_ops rx8010_rtc_ops = {
+	.read_time = rx8010_get_time,
+	.set_time = rx8010_set_time,
+	.ioctl = rx8010_ioctl,
+	.read_alarm = rx8010_read_alarm,
+	.set_alarm = rx8010_set_alarm,
+	.alarm_irq_enable = rx8010_alarm_irq_enable,
+};
+
+static const struct regmap_config rx8010_regmap_config = {
+	.name = "rx8010-rtc",
+	.reg_bits = 8,
+	.val_bits = 8,
+};
+
+static int rx8010_probe(struct i2c_client *client)
+{
+	struct device *dev = &client->dev;
+	struct rx8010_data *rx8010;
+	int err = 0;
+
+	rx8010 = devm_kzalloc(dev, sizeof(*rx8010), GFP_KERNEL);
+	if (!rx8010)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, rx8010);
+
+	rx8010->regs = devm_regmap_init_i2c(client, &rx8010_regmap_config);
+	if (IS_ERR(rx8010->regs))
+		return PTR_ERR(rx8010->regs);
+
+	err = rx8010_init(dev);
+	if (err)
+		return err;
+
+	rx8010->rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(rx8010->rtc))
+		return PTR_ERR(rx8010->rtc);
+
+	if (client->irq > 0) {
+		unsigned long irqflags = IRQF_TRIGGER_LOW;
+
+		if (dev_fwnode(&client->dev))
+			irqflags = 0;
+
+		err = devm_request_threaded_irq(dev, client->irq, NULL,
+						rx8010_irq_1_handler,
+						irqflags | IRQF_ONESHOT,
+						"rx8010", client);
+		if (err) {
+			dev_err(dev, "unable to request IRQ\n");
+			return err;
+		}
+	} else {
+		clear_bit(RTC_FEATURE_ALARM, rx8010->rtc->features);
+	}
+
+	rx8010->rtc->ops = &rx8010_rtc_ops;
+	rx8010->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	rx8010->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	return devm_rtc_register_device(rx8010->rtc);
+}
+
+static struct i2c_driver rx8010_driver = {
+	.driver = {
+		.name = "rtc-rx8010",
+		.of_match_table = of_match_ptr(rx8010_of_match),
+	},
+	.probe		= rx8010_probe,
+	.id_table	= rx8010_id,
+};
+
+module_i2c_driver(rx8010_driver);
+
+MODULE_AUTHOR("Akshay Bhat <akshay.bhat@timesys.com>");
+MODULE_DESCRIPTION("Epson RX8010SJ RTC driver");
+MODULE_LICENSE("GPL v2");