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, 368 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1511.c b/drivers/rtc/rtc-ds1511.c
new file mode 100644
index 000000000..8b087d955
--- /dev/null
+++ b/drivers/rtc/rtc-ds1511.c
@@ -0,0 +1,368 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * An rtc driver for the Dallas DS1511
+ *
+ * Copyright (C) 2006 Atsushi Nemoto <anemo@mba.ocn.ne.jp>
+ * Copyright (C) 2007 Andrew Sharp <andy.sharp@lsi.com>
+ *
+ * Real time clock driver for the Dallas 1511 chip, which also
+ * contains a watchdog timer.  There is a tiny amount of code that
+ * platform code could use to mess with the watchdog device a little
+ * bit, but not a full watchdog driver.
+ */
+
+#include <linux/bcd.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/gfp.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/io.h>
+#include <linux/module.h>
+
+#define DS1511_SEC		0x0
+#define DS1511_MIN		0x1
+#define DS1511_HOUR		0x2
+#define DS1511_DOW		0x3
+#define DS1511_DOM		0x4
+#define DS1511_MONTH		0x5
+#define DS1511_YEAR		0x6
+#define DS1511_CENTURY		0x7
+#define DS1511_AM1_SEC		0x8
+#define DS1511_AM2_MIN		0x9
+#define DS1511_AM3_HOUR		0xa
+#define DS1511_AM4_DATE		0xb
+#define DS1511_WD_MSEC		0xc
+#define DS1511_WD_SEC		0xd
+#define DS1511_CONTROL_A	0xe
+#define DS1511_CONTROL_B	0xf
+#define DS1511_RAMADDR_LSB	0x10
+#define DS1511_RAMDATA		0x13
+
+#define DS1511_BLF1	0x80
+#define DS1511_BLF2	0x40
+#define DS1511_PRS	0x20
+#define DS1511_PAB	0x10
+#define DS1511_TDF	0x08
+#define DS1511_KSF	0x04
+#define DS1511_WDF	0x02
+#define DS1511_IRQF	0x01
+#define DS1511_TE	0x80
+#define DS1511_CS	0x40
+#define DS1511_BME	0x20
+#define DS1511_TPE	0x10
+#define DS1511_TIE	0x08
+#define DS1511_KIE	0x04
+#define DS1511_WDE	0x02
+#define DS1511_WDS	0x01
+#define DS1511_RAM_MAX	0x100
+
+struct ds1511_data {
+	struct rtc_device *rtc;
+	void __iomem *ioaddr;		/* virtual base address */
+	int irq;
+	spinlock_t lock;
+};
+
+static DEFINE_SPINLOCK(ds1511_lock);
+
+static __iomem char *ds1511_base;
+static u32 reg_spacing = 1;
+
+static void rtc_write(uint8_t val, uint32_t reg)
+{
+	writeb(val, ds1511_base + (reg * reg_spacing));
+}
+
+static uint8_t rtc_read(uint32_t reg)
+{
+	return readb(ds1511_base + (reg * reg_spacing));
+}
+
+static void rtc_disable_update(void)
+{
+	rtc_write((rtc_read(DS1511_CONTROL_B) & ~DS1511_TE), DS1511_CONTROL_B);
+}
+
+static void rtc_enable_update(void)
+{
+	rtc_write((rtc_read(DS1511_CONTROL_B) | DS1511_TE), DS1511_CONTROL_B);
+}
+
+static int ds1511_rtc_set_time(struct device *dev, struct rtc_time *rtc_tm)
+{
+	u8 mon, day, dow, hrs, min, sec, yrs, cen;
+	unsigned long flags;
+
+	yrs = rtc_tm->tm_year % 100;
+	cen = 19 + rtc_tm->tm_year / 100;
+	mon = rtc_tm->tm_mon + 1;   /* tm_mon starts at zero */
+	day = rtc_tm->tm_mday;
+	dow = rtc_tm->tm_wday & 0x7; /* automatic BCD */
+	hrs = rtc_tm->tm_hour;
+	min = rtc_tm->tm_min;
+	sec = rtc_tm->tm_sec;
+
+	/*
+	 * each register is a different number of valid bits
+	 */
+	sec = bin2bcd(sec) & 0x7f;
+	min = bin2bcd(min) & 0x7f;
+	hrs = bin2bcd(hrs) & 0x3f;
+	day = bin2bcd(day) & 0x3f;
+	mon = bin2bcd(mon) & 0x1f;
+	yrs = bin2bcd(yrs) & 0xff;
+	cen = bin2bcd(cen) & 0xff;
+
+	spin_lock_irqsave(&ds1511_lock, flags);
+	rtc_disable_update();
+	rtc_write(cen, DS1511_CENTURY);
+	rtc_write(yrs, DS1511_YEAR);
+	rtc_write((rtc_read(DS1511_MONTH) & 0xe0) | mon, DS1511_MONTH);
+	rtc_write(day, DS1511_DOM);
+	rtc_write(hrs, DS1511_HOUR);
+	rtc_write(min, DS1511_MIN);
+	rtc_write(sec, DS1511_SEC);
+	rtc_write(dow, DS1511_DOW);
+	rtc_enable_update();
+	spin_unlock_irqrestore(&ds1511_lock, flags);
+
+	return 0;
+}
+
+static int ds1511_rtc_read_time(struct device *dev, struct rtc_time *rtc_tm)
+{
+	unsigned int century;
+	unsigned long flags;
+
+	spin_lock_irqsave(&ds1511_lock, flags);
+	rtc_disable_update();
+
+	rtc_tm->tm_sec = rtc_read(DS1511_SEC) & 0x7f;
+	rtc_tm->tm_min = rtc_read(DS1511_MIN) & 0x7f;
+	rtc_tm->tm_hour = rtc_read(DS1511_HOUR) & 0x3f;
+	rtc_tm->tm_mday = rtc_read(DS1511_DOM) & 0x3f;
+	rtc_tm->tm_wday = rtc_read(DS1511_DOW) & 0x7;
+	rtc_tm->tm_mon = rtc_read(DS1511_MONTH) & 0x1f;
+	rtc_tm->tm_year = rtc_read(DS1511_YEAR) & 0x7f;
+	century = rtc_read(DS1511_CENTURY);
+
+	rtc_enable_update();
+	spin_unlock_irqrestore(&ds1511_lock, flags);
+
+	rtc_tm->tm_sec = bcd2bin(rtc_tm->tm_sec);
+	rtc_tm->tm_min = bcd2bin(rtc_tm->tm_min);
+	rtc_tm->tm_hour = bcd2bin(rtc_tm->tm_hour);
+	rtc_tm->tm_mday = bcd2bin(rtc_tm->tm_mday);
+	rtc_tm->tm_wday = bcd2bin(rtc_tm->tm_wday);
+	rtc_tm->tm_mon = bcd2bin(rtc_tm->tm_mon);
+	rtc_tm->tm_year = bcd2bin(rtc_tm->tm_year);
+	century = bcd2bin(century) * 100;
+
+	/*
+	 * Account for differences between how the RTC uses the values
+	 * and how they are defined in a struct rtc_time;
+	 */
+	century += rtc_tm->tm_year;
+	rtc_tm->tm_year = century - 1900;
+
+	rtc_tm->tm_mon--;
+
+	return 0;
+}
+
+static void ds1511_rtc_alarm_enable(unsigned int enabled)
+{
+	rtc_write(rtc_read(DS1511_CONTROL_B) | (enabled ? DS1511_TIE : 0), DS1511_CONTROL_B);
+}
+
+static int ds1511_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct ds1511_data *ds1511 = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&ds1511->lock, flags);
+	rtc_write(bin2bcd(alrm->time.tm_mday) & 0x3f, DS1511_AM4_DATE);
+	rtc_write(bin2bcd(alrm->time.tm_hour) & 0x3f, DS1511_AM3_HOUR);
+	rtc_write(bin2bcd(alrm->time.tm_min) & 0x7f, DS1511_AM2_MIN);
+	rtc_write(bin2bcd(alrm->time.tm_sec) & 0x7f, DS1511_AM1_SEC);
+	ds1511_rtc_alarm_enable(alrm->enabled);
+
+	rtc_read(DS1511_CONTROL_A);	/* clear interrupts */
+	spin_unlock_irqrestore(&ds1511->lock, flags);
+
+	return 0;
+}
+
+static int ds1511_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	alrm->time.tm_mday = bcd2bin(rtc_read(DS1511_AM4_DATE) & 0x3f);
+	alrm->time.tm_hour = bcd2bin(rtc_read(DS1511_AM3_HOUR) & 0x3f);
+	alrm->time.tm_min = bcd2bin(rtc_read(DS1511_AM2_MIN) & 0x7f);
+	alrm->time.tm_sec = bcd2bin(rtc_read(DS1511_AM1_SEC) & 0x7f);
+	alrm->enabled = !!(rtc_read(DS1511_CONTROL_B) & DS1511_TIE);
+
+	return 0;
+}
+
+static irqreturn_t ds1511_interrupt(int irq, void *dev_id)
+{
+	struct platform_device *pdev = dev_id;
+	struct ds1511_data *ds1511 = platform_get_drvdata(pdev);
+	unsigned long events = 0;
+
+	spin_lock(&ds1511->lock);
+	/*
+	 * read and clear interrupt
+	 */
+	if (rtc_read(DS1511_CONTROL_A) & DS1511_IRQF) {
+		events = RTC_IRQF | RTC_AF;
+		rtc_update_irq(ds1511->rtc, 1, events);
+	}
+	spin_unlock(&ds1511->lock);
+	return events ? IRQ_HANDLED : IRQ_NONE;
+}
+
+static int ds1511_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct ds1511_data *ds1511 = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&ds1511->lock, flags);
+	ds1511_rtc_alarm_enable(enabled);
+	spin_unlock_irqrestore(&ds1511->lock, flags);
+
+	return 0;
+}
+
+static const struct rtc_class_ops ds1511_rtc_ops = {
+	.read_time		= ds1511_rtc_read_time,
+	.set_time		= ds1511_rtc_set_time,
+	.read_alarm		= ds1511_rtc_read_alarm,
+	.set_alarm		= ds1511_rtc_set_alarm,
+	.alarm_irq_enable	= ds1511_rtc_alarm_irq_enable,
+};
+
+static int ds1511_nvram_read(void *priv, unsigned int pos, void *buf,
+			     size_t size)
+{
+	int i;
+
+	rtc_write(pos, DS1511_RAMADDR_LSB);
+	for (i = 0; i < size; i++)
+		*(char *)buf++ = rtc_read(DS1511_RAMDATA);
+
+	return 0;
+}
+
+static int ds1511_nvram_write(void *priv, unsigned int pos, void *buf,
+			      size_t size)
+{
+	int i;
+
+	rtc_write(pos, DS1511_RAMADDR_LSB);
+	for (i = 0; i < size; i++)
+		rtc_write(*(char *)buf++, DS1511_RAMDATA);
+
+	return 0;
+}
+
+static int ds1511_rtc_probe(struct platform_device *pdev)
+{
+	struct ds1511_data *ds1511;
+	int ret = 0;
+	struct nvmem_config ds1511_nvmem_cfg = {
+		.name = "ds1511_nvram",
+		.word_size = 1,
+		.stride = 1,
+		.size = DS1511_RAM_MAX,
+		.reg_read = ds1511_nvram_read,
+		.reg_write = ds1511_nvram_write,
+		.priv = &pdev->dev,
+	};
+
+	ds1511 = devm_kzalloc(&pdev->dev, sizeof(*ds1511), GFP_KERNEL);
+	if (!ds1511)
+		return -ENOMEM;
+
+	ds1511_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(ds1511_base))
+		return PTR_ERR(ds1511_base);
+	ds1511->ioaddr = ds1511_base;
+	ds1511->irq = platform_get_irq(pdev, 0);
+
+	/*
+	 * turn on the clock and the crystal, etc.
+	 */
+	rtc_write(DS1511_BME, DS1511_CONTROL_B);
+	rtc_write(0, DS1511_CONTROL_A);
+	/*
+	 * clear the wdog counter
+	 */
+	rtc_write(0, DS1511_WD_MSEC);
+	rtc_write(0, DS1511_WD_SEC);
+	/*
+	 * start the clock
+	 */
+	rtc_enable_update();
+
+	/*
+	 * check for a dying bat-tree
+	 */
+	if (rtc_read(DS1511_CONTROL_A) & DS1511_BLF1)
+		dev_warn(&pdev->dev, "voltage-low detected.\n");
+
+	spin_lock_init(&ds1511->lock);
+	platform_set_drvdata(pdev, ds1511);
+
+	ds1511->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(ds1511->rtc))
+		return PTR_ERR(ds1511->rtc);
+
+	ds1511->rtc->ops = &ds1511_rtc_ops;
+	ds1511->rtc->range_max = RTC_TIMESTAMP_END_2099;
+	ds1511->rtc->alarm_offset_max = 28 * 24 * 60 * 60 - 1;
+
+	/*
+	 * if the platform has an interrupt in mind for this device,
+	 * then by all means, set it
+	 */
+	if (ds1511->irq > 0) {
+		rtc_read(DS1511_CONTROL_A);
+		if (devm_request_irq(&pdev->dev, ds1511->irq, ds1511_interrupt,
+			IRQF_SHARED, pdev->name, pdev) < 0) {
+
+			dev_warn(&pdev->dev, "interrupt not available.\n");
+			ds1511->irq = 0;
+		}
+	}
+
+	if (ds1511->irq == 0)
+		clear_bit(RTC_FEATURE_ALARM, ds1511->rtc->features);
+
+	ret = devm_rtc_register_device(ds1511->rtc);
+	if (ret)
+		return ret;
+
+	devm_rtc_nvmem_register(ds1511->rtc, &ds1511_nvmem_cfg);
+
+	return 0;
+}
+
+/* work with hotplug and coldplug */
+MODULE_ALIAS("platform:ds1511");
+
+static struct platform_driver ds1511_rtc_driver = {
+	.probe		= ds1511_rtc_probe,
+	.driver		= {
+		.name	= "ds1511",
+	},
+};
+
+module_platform_driver(ds1511_rtc_driver);
+
+MODULE_AUTHOR("Andrew Sharp <andy.sharp@lsi.com>");
+MODULE_DESCRIPTION("Dallas DS1511 RTC driver");
+MODULE_LICENSE("GPL");