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, 477 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1343.c b/drivers/rtc/rtc-ds1343.c
new file mode 100644
index 000000000..aa9500791
--- /dev/null
+++ b/drivers/rtc/rtc-ds1343.c
@@ -0,0 +1,477 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/* rtc-ds1343.c
+ *
+ * Driver for Dallas Semiconductor DS1343 Low Current, SPI Compatible
+ * Real Time Clock
+ *
+ * Author : Raghavendra Chandra Ganiga <ravi23ganiga@gmail.com>
+ *	    Ankur Srivastava <sankurece@gmail.com> : DS1343 Nvram Support
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/device.h>
+#include <linux/spi/spi.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/bcd.h>
+#include <linux/pm.h>
+#include <linux/pm_wakeirq.h>
+#include <linux/slab.h>
+
+#define DALLAS_MAXIM_DS1343	0
+#define DALLAS_MAXIM_DS1344	1
+
+/* RTC DS1343 Registers */
+#define DS1343_SECONDS_REG	0x00
+#define DS1343_MINUTES_REG	0x01
+#define DS1343_HOURS_REG	0x02
+#define DS1343_DAY_REG		0x03
+#define DS1343_DATE_REG		0x04
+#define DS1343_MONTH_REG	0x05
+#define DS1343_YEAR_REG		0x06
+#define DS1343_ALM0_SEC_REG	0x07
+#define DS1343_ALM0_MIN_REG	0x08
+#define DS1343_ALM0_HOUR_REG	0x09
+#define DS1343_ALM0_DAY_REG	0x0A
+#define DS1343_ALM1_SEC_REG	0x0B
+#define DS1343_ALM1_MIN_REG	0x0C
+#define DS1343_ALM1_HOUR_REG	0x0D
+#define DS1343_ALM1_DAY_REG	0x0E
+#define DS1343_CONTROL_REG	0x0F
+#define DS1343_STATUS_REG	0x10
+#define DS1343_TRICKLE_REG	0x11
+#define DS1343_NVRAM		0x20
+
+#define DS1343_NVRAM_LEN	96
+
+/* DS1343 Control Registers bits */
+#define DS1343_EOSC		0x80
+#define DS1343_DOSF		0x20
+#define DS1343_EGFIL		0x10
+#define DS1343_SQW		0x08
+#define DS1343_INTCN		0x04
+#define DS1343_A1IE		0x02
+#define DS1343_A0IE		0x01
+
+/* DS1343 Status Registers bits */
+#define DS1343_OSF		0x80
+#define DS1343_IRQF1		0x02
+#define DS1343_IRQF0		0x01
+
+/* DS1343 Trickle Charger Registers bits */
+#define DS1343_TRICKLE_MAGIC	0xa0
+#define DS1343_TRICKLE_DS1	0x08
+#define DS1343_TRICKLE_1K	0x01
+#define DS1343_TRICKLE_2K	0x02
+#define DS1343_TRICKLE_4K	0x03
+
+static const struct spi_device_id ds1343_id[] = {
+	{ "ds1343", DALLAS_MAXIM_DS1343 },
+	{ "ds1344", DALLAS_MAXIM_DS1344 },
+	{ }
+};
+MODULE_DEVICE_TABLE(spi, ds1343_id);
+
+struct ds1343_priv {
+	struct rtc_device *rtc;
+	struct regmap *map;
+	int irq;
+};
+
+static ssize_t ds1343_show_glitchfilter(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev->parent);
+	int glitch_filt_status, data;
+	int res;
+
+	res = regmap_read(priv->map, DS1343_CONTROL_REG, &data);
+	if (res)
+		return res;
+
+	glitch_filt_status = !!(data & DS1343_EGFIL);
+
+	if (glitch_filt_status)
+		return sprintf(buf, "enabled\n");
+	else
+		return sprintf(buf, "disabled\n");
+}
+
+static ssize_t ds1343_store_glitchfilter(struct device *dev,
+					struct device_attribute *attr,
+					const char *buf, size_t count)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev->parent);
+	int data = 0;
+	int res;
+
+	if (strncmp(buf, "enabled", 7) == 0)
+		data = DS1343_EGFIL;
+	else if (strncmp(buf, "disabled", 8))
+		return -EINVAL;
+
+	res = regmap_update_bits(priv->map, DS1343_CONTROL_REG,
+				 DS1343_EGFIL, data);
+	if (res)
+		return res;
+
+	return count;
+}
+
+static DEVICE_ATTR(glitch_filter, S_IRUGO | S_IWUSR, ds1343_show_glitchfilter,
+			ds1343_store_glitchfilter);
+
+static int ds1343_nvram_write(void *priv, unsigned int off, void *val,
+			      size_t bytes)
+{
+	struct ds1343_priv *ds1343 = priv;
+
+	return regmap_bulk_write(ds1343->map, DS1343_NVRAM + off, val, bytes);
+}
+
+static int ds1343_nvram_read(void *priv, unsigned int off, void *val,
+			     size_t bytes)
+{
+	struct ds1343_priv *ds1343 = priv;
+
+	return regmap_bulk_read(ds1343->map, DS1343_NVRAM + off, val, bytes);
+}
+
+static ssize_t ds1343_show_tricklecharger(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev->parent);
+	int res, data;
+	char *diodes = "disabled", *resistors = " ";
+
+	res = regmap_read(priv->map, DS1343_TRICKLE_REG, &data);
+	if (res)
+		return res;
+
+	if ((data & 0xf0) == DS1343_TRICKLE_MAGIC) {
+		switch (data & 0x0c) {
+		case DS1343_TRICKLE_DS1:
+			diodes = "one diode,";
+			break;
+
+		default:
+			diodes = "no diode,";
+			break;
+		}
+
+		switch (data & 0x03) {
+		case DS1343_TRICKLE_1K:
+			resistors = "1k Ohm";
+			break;
+
+		case DS1343_TRICKLE_2K:
+			resistors = "2k Ohm";
+			break;
+
+		case DS1343_TRICKLE_4K:
+			resistors = "4k Ohm";
+			break;
+
+		default:
+			diodes = "disabled";
+			break;
+		}
+	}
+
+	return sprintf(buf, "%s %s\n", diodes, resistors);
+}
+
+static DEVICE_ATTR(trickle_charger, S_IRUGO, ds1343_show_tricklecharger, NULL);
+
+static struct attribute *ds1343_attrs[] = {
+	&dev_attr_glitch_filter.attr,
+	&dev_attr_trickle_charger.attr,
+	NULL
+};
+
+static const struct attribute_group ds1343_attr_group = {
+	.attrs  = ds1343_attrs,
+};
+
+static int ds1343_read_time(struct device *dev, struct rtc_time *dt)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev);
+	unsigned char buf[7];
+	int res;
+
+	res = regmap_bulk_read(priv->map, DS1343_SECONDS_REG, buf, 7);
+	if (res)
+		return res;
+
+	dt->tm_sec	= bcd2bin(buf[0]);
+	dt->tm_min	= bcd2bin(buf[1]);
+	dt->tm_hour	= bcd2bin(buf[2] & 0x3F);
+	dt->tm_wday	= bcd2bin(buf[3]) - 1;
+	dt->tm_mday	= bcd2bin(buf[4]);
+	dt->tm_mon	= bcd2bin(buf[5] & 0x1F) - 1;
+	dt->tm_year	= bcd2bin(buf[6]) + 100; /* year offset from 1900 */
+
+	return 0;
+}
+
+static int ds1343_set_time(struct device *dev, struct rtc_time *dt)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev);
+	u8 buf[7];
+
+	buf[0] = bin2bcd(dt->tm_sec);
+	buf[1] = bin2bcd(dt->tm_min);
+	buf[2] = bin2bcd(dt->tm_hour) & 0x3F;
+	buf[3] = bin2bcd(dt->tm_wday + 1);
+	buf[4] = bin2bcd(dt->tm_mday);
+	buf[5] = bin2bcd(dt->tm_mon + 1);
+	buf[6] = bin2bcd(dt->tm_year - 100);
+
+	return regmap_bulk_write(priv->map, DS1343_SECONDS_REG,
+				 buf, sizeof(buf));
+}
+
+static int ds1343_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	unsigned int val;
+	int res;
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	res = regmap_read(priv->map, DS1343_STATUS_REG, &val);
+	if (res)
+		return res;
+
+	alarm->pending = !!(val & DS1343_IRQF0);
+
+	res = regmap_read(priv->map, DS1343_CONTROL_REG, &val);
+	if (res)
+		return res;
+	alarm->enabled = !!(val & DS1343_A0IE);
+
+	res = regmap_bulk_read(priv->map, DS1343_ALM0_SEC_REG, buf, 4);
+	if (res)
+		return res;
+
+	alarm->time.tm_sec = bcd2bin(buf[0]) & 0x7f;
+	alarm->time.tm_min = bcd2bin(buf[1]) & 0x7f;
+	alarm->time.tm_hour = bcd2bin(buf[2]) & 0x3f;
+	alarm->time.tm_mday = bcd2bin(buf[3]) & 0x3f;
+
+	return 0;
+}
+
+static int ds1343_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev);
+	unsigned char buf[4];
+	int res = 0;
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	res = regmap_update_bits(priv->map, DS1343_CONTROL_REG, DS1343_A0IE, 0);
+	if (res)
+		return res;
+
+	buf[0] = bin2bcd(alarm->time.tm_sec);
+	buf[1] = bin2bcd(alarm->time.tm_min);
+	buf[2] = bin2bcd(alarm->time.tm_hour);
+	buf[3] = bin2bcd(alarm->time.tm_mday);
+
+	res = regmap_bulk_write(priv->map, DS1343_ALM0_SEC_REG, buf, 4);
+	if (res)
+		return res;
+
+	if (alarm->enabled)
+		res = regmap_update_bits(priv->map, DS1343_CONTROL_REG,
+					 DS1343_A0IE, DS1343_A0IE);
+
+	return res;
+}
+
+static int ds1343_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct ds1343_priv *priv = dev_get_drvdata(dev);
+
+	if (priv->irq <= 0)
+		return -EINVAL;
+
+	return regmap_update_bits(priv->map, DS1343_CONTROL_REG,
+				  DS1343_A0IE, enabled ? DS1343_A0IE : 0);
+}
+
+static irqreturn_t ds1343_thread(int irq, void *dev_id)
+{
+	struct ds1343_priv *priv = dev_id;
+	unsigned int stat;
+	int res = 0;
+
+	rtc_lock(priv->rtc);
+
+	res = regmap_read(priv->map, DS1343_STATUS_REG, &stat);
+	if (res)
+		goto out;
+
+	if (stat & DS1343_IRQF0) {
+		stat &= ~DS1343_IRQF0;
+		regmap_write(priv->map, DS1343_STATUS_REG, stat);
+
+		rtc_update_irq(priv->rtc, 1, RTC_AF | RTC_IRQF);
+
+		regmap_update_bits(priv->map, DS1343_CONTROL_REG,
+				   DS1343_A0IE, 0);
+	}
+
+out:
+	rtc_unlock(priv->rtc);
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops ds1343_rtc_ops = {
+	.read_time	= ds1343_read_time,
+	.set_time	= ds1343_set_time,
+	.read_alarm	= ds1343_read_alarm,
+	.set_alarm	= ds1343_set_alarm,
+	.alarm_irq_enable = ds1343_alarm_irq_enable,
+};
+
+static int ds1343_probe(struct spi_device *spi)
+{
+	struct ds1343_priv *priv;
+	struct regmap_config config = { .reg_bits = 8, .val_bits = 8,
+					.write_flag_mask = 0x80, };
+	unsigned int data;
+	int res;
+	struct nvmem_config nvmem_cfg = {
+		.name = "ds1343-",
+		.word_size = 1,
+		.stride = 1,
+		.size = DS1343_NVRAM_LEN,
+		.reg_read = ds1343_nvram_read,
+		.reg_write = ds1343_nvram_write,
+	};
+
+	priv = devm_kzalloc(&spi->dev, sizeof(struct ds1343_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	/* RTC DS1347 works in spi mode 3 and
+	 * its chip select is active high. Active high should be defined as
+	 * "inverse polarity" as GPIO-based chip selects can be logically
+	 * active high but inverted by the GPIO library.
+	 */
+	spi->mode |= SPI_MODE_3;
+	spi->mode ^= SPI_CS_HIGH;
+	spi->bits_per_word = 8;
+	res = spi_setup(spi);
+	if (res)
+		return res;
+
+	spi_set_drvdata(spi, priv);
+
+	priv->map = devm_regmap_init_spi(spi, &config);
+
+	if (IS_ERR(priv->map)) {
+		dev_err(&spi->dev, "spi regmap init failed for rtc ds1343\n");
+		return PTR_ERR(priv->map);
+	}
+
+	res = regmap_read(priv->map, DS1343_SECONDS_REG, &data);
+	if (res)
+		return res;
+
+	regmap_read(priv->map, DS1343_CONTROL_REG, &data);
+	data |= DS1343_INTCN;
+	data &= ~(DS1343_EOSC | DS1343_A1IE | DS1343_A0IE);
+	regmap_write(priv->map, DS1343_CONTROL_REG, data);
+
+	regmap_read(priv->map, DS1343_STATUS_REG, &data);
+	data &= ~(DS1343_OSF | DS1343_IRQF1 | DS1343_IRQF0);
+	regmap_write(priv->map, DS1343_STATUS_REG, data);
+
+	priv->rtc = devm_rtc_allocate_device(&spi->dev);
+	if (IS_ERR(priv->rtc))
+		return PTR_ERR(priv->rtc);
+
+	priv->rtc->ops = &ds1343_rtc_ops;
+	priv->rtc->range_min = RTC_TIMESTAMP_BEGIN_2000;
+	priv->rtc->range_max = RTC_TIMESTAMP_END_2099;
+
+	res = rtc_add_group(priv->rtc, &ds1343_attr_group);
+	if (res)
+		dev_err(&spi->dev,
+			"unable to create sysfs entries for rtc ds1343\n");
+
+	res = devm_rtc_register_device(priv->rtc);
+	if (res)
+		return res;
+
+	nvmem_cfg.priv = priv;
+	devm_rtc_nvmem_register(priv->rtc, &nvmem_cfg);
+
+	priv->irq = spi->irq;
+
+	if (priv->irq >= 0) {
+		res = devm_request_threaded_irq(&spi->dev, spi->irq, NULL,
+						ds1343_thread, IRQF_ONESHOT,
+						"ds1343", priv);
+		if (res) {
+			priv->irq = -1;
+			dev_err(&spi->dev,
+				"unable to request irq for rtc ds1343\n");
+		} else {
+			device_init_wakeup(&spi->dev, true);
+			devm_pm_set_wake_irq(&spi->dev, spi->irq);
+		}
+	}
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+
+static int ds1343_suspend(struct device *dev)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	if (spi->irq >= 0 && device_may_wakeup(dev))
+		enable_irq_wake(spi->irq);
+
+	return 0;
+}
+
+static int ds1343_resume(struct device *dev)
+{
+	struct spi_device *spi = to_spi_device(dev);
+
+	if (spi->irq >= 0 && device_may_wakeup(dev))
+		disable_irq_wake(spi->irq);
+
+	return 0;
+}
+
+#endif
+
+static SIMPLE_DEV_PM_OPS(ds1343_pm, ds1343_suspend, ds1343_resume);
+
+static struct spi_driver ds1343_driver = {
+	.driver = {
+		.name = "ds1343",
+		.pm = &ds1343_pm,
+	},
+	.probe = ds1343_probe,
+	.id_table = ds1343_id,
+};
+
+module_spi_driver(ds1343_driver);
+
+MODULE_DESCRIPTION("DS1343 RTC SPI Driver");
+MODULE_AUTHOR("Raghavendra Chandra Ganiga <ravi23ganiga@gmail.com>,"
+		"Ankur Srivastava <sankurece@gmail.com>");
+MODULE_LICENSE("GPL v2");