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, 358 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1286.c b/drivers/rtc/rtc-ds1286.c
new file mode 100644
index 000000000..7acf849d4
--- /dev/null
+++ b/drivers/rtc/rtc-ds1286.c
@@ -0,0 +1,358 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * DS1286 Real Time Clock interface for Linux
+ *
+ * Copyright (C) 1998, 1999, 2000 Ralf Baechle
+ * Copyright (C) 2008 Thomas Bogendoerfer
+ *
+ * Based on code written by Paul Gortmaker.
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/bcd.h>
+#include <linux/rtc/ds1286.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+
+struct ds1286_priv {
+	struct rtc_device *rtc;
+	u32 __iomem *rtcregs;
+	spinlock_t lock;
+};
+
+static inline u8 ds1286_rtc_read(struct ds1286_priv *priv, int reg)
+{
+	return __raw_readl(&priv->rtcregs[reg]) & 0xff;
+}
+
+static inline void ds1286_rtc_write(struct ds1286_priv *priv, u8 data, int reg)
+{
+	__raw_writel(data, &priv->rtcregs[reg]);
+}
+
+
+static int ds1286_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	unsigned char val;
+
+	/* Allow or mask alarm interrupts */
+	spin_lock_irqsave(&priv->lock, flags);
+	val = ds1286_rtc_read(priv, RTC_CMD);
+	if (enabled)
+		val &=  ~RTC_TDM;
+	else
+		val |=  RTC_TDM;
+	ds1286_rtc_write(priv, val, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+#ifdef CONFIG_RTC_INTF_DEV
+
+static int ds1286_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	unsigned char val;
+
+	switch (cmd) {
+	case RTC_WIE_OFF:
+		/* Mask watchdog int. enab. bit	*/
+		spin_lock_irqsave(&priv->lock, flags);
+		val = ds1286_rtc_read(priv, RTC_CMD);
+		val |= RTC_WAM;
+		ds1286_rtc_write(priv, val, RTC_CMD);
+		spin_unlock_irqrestore(&priv->lock, flags);
+		break;
+	case RTC_WIE_ON:
+		/* Allow watchdog interrupts.	*/
+		spin_lock_irqsave(&priv->lock, flags);
+		val = ds1286_rtc_read(priv, RTC_CMD);
+		val &= ~RTC_WAM;
+		ds1286_rtc_write(priv, val, RTC_CMD);
+		spin_unlock_irqrestore(&priv->lock, flags);
+		break;
+	default:
+		return -ENOIOCTLCMD;
+	}
+	return 0;
+}
+
+#else
+#define ds1286_ioctl    NULL
+#endif
+
+#ifdef CONFIG_PROC_FS
+
+static int ds1286_proc(struct device *dev, struct seq_file *seq)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char month, cmd, amode;
+	const char *s;
+
+	month = ds1286_rtc_read(priv, RTC_MONTH);
+	seq_printf(seq,
+		   "oscillator\t: %s\n"
+		   "square_wave\t: %s\n",
+		   (month & RTC_EOSC) ? "disabled" : "enabled",
+		   (month & RTC_ESQW) ? "disabled" : "enabled");
+
+	amode = ((ds1286_rtc_read(priv, RTC_MINUTES_ALARM) & 0x80) >> 5) |
+		((ds1286_rtc_read(priv, RTC_HOURS_ALARM) & 0x80) >> 6) |
+		((ds1286_rtc_read(priv, RTC_DAY_ALARM) & 0x80) >> 7);
+	switch (amode) {
+	case 7:
+		s = "each minute";
+		break;
+	case 3:
+		s = "minutes match";
+		break;
+	case 1:
+		s = "hours and minutes match";
+		break;
+	case 0:
+		s = "days, hours and minutes match";
+		break;
+	default:
+		s = "invalid";
+		break;
+	}
+	seq_printf(seq, "alarm_mode\t: %s\n", s);
+
+	cmd = ds1286_rtc_read(priv, RTC_CMD);
+	seq_printf(seq,
+		   "alarm_enable\t: %s\n"
+		   "wdog_alarm\t: %s\n"
+		   "alarm_mask\t: %s\n"
+		   "wdog_alarm_mask\t: %s\n"
+		   "interrupt_mode\t: %s\n"
+		   "INTB_mode\t: %s_active\n"
+		   "interrupt_pins\t: %s\n",
+		   (cmd & RTC_TDF) ? "yes" : "no",
+		   (cmd & RTC_WAF) ? "yes" : "no",
+		   (cmd & RTC_TDM) ? "disabled" : "enabled",
+		   (cmd & RTC_WAM) ? "disabled" : "enabled",
+		   (cmd & RTC_PU_LVL) ? "pulse" : "level",
+		   (cmd & RTC_IBH_LO) ? "low" : "high",
+		   (cmd & RTC_IPSW) ? "unswapped" : "swapped");
+	return 0;
+}
+
+#else
+#define ds1286_proc     NULL
+#endif
+
+static int ds1286_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char save_control;
+	unsigned long flags;
+	unsigned long uip_watchdog = jiffies;
+
+	/*
+	 * read RTC once any update in progress is done. The update
+	 * can take just over 2ms. We wait 10 to 20ms. There is no need to
+	 * to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
+	 * If you need to know *exactly* when a second has started, enable
+	 * periodic update complete interrupts, (via ioctl) and then
+	 * immediately read /dev/rtc which will block until you get the IRQ.
+	 * Once the read clears, read the RTC time (again via ioctl). Easy.
+	 */
+
+	if (ds1286_rtc_read(priv, RTC_CMD) & RTC_TE)
+		while (time_before(jiffies, uip_watchdog + 2*HZ/100))
+			barrier();
+
+	/*
+	 * Only the values that we read from the RTC are set. We leave
+	 * tm_wday, tm_yday and tm_isdst untouched. Even though the
+	 * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
+	 * by the RTC when initially set to a non-zero value.
+	 */
+	spin_lock_irqsave(&priv->lock, flags);
+	save_control = ds1286_rtc_read(priv, RTC_CMD);
+	ds1286_rtc_write(priv, (save_control|RTC_TE), RTC_CMD);
+
+	tm->tm_sec = ds1286_rtc_read(priv, RTC_SECONDS);
+	tm->tm_min = ds1286_rtc_read(priv, RTC_MINUTES);
+	tm->tm_hour = ds1286_rtc_read(priv, RTC_HOURS) & 0x3f;
+	tm->tm_mday = ds1286_rtc_read(priv, RTC_DATE);
+	tm->tm_mon = ds1286_rtc_read(priv, RTC_MONTH) & 0x1f;
+	tm->tm_year = ds1286_rtc_read(priv, RTC_YEAR);
+
+	ds1286_rtc_write(priv, save_control, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	tm->tm_sec = bcd2bin(tm->tm_sec);
+	tm->tm_min = bcd2bin(tm->tm_min);
+	tm->tm_hour = bcd2bin(tm->tm_hour);
+	tm->tm_mday = bcd2bin(tm->tm_mday);
+	tm->tm_mon = bcd2bin(tm->tm_mon);
+	tm->tm_year = bcd2bin(tm->tm_year);
+
+	/*
+	 * Account for differences between how the RTC uses the values
+	 * and how they are defined in a struct rtc_time;
+	 */
+	if (tm->tm_year < 45)
+		tm->tm_year += 30;
+	tm->tm_year += 40;
+	if (tm->tm_year < 70)
+		tm->tm_year += 100;
+
+	tm->tm_mon--;
+
+	return 0;
+}
+
+static int ds1286_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char mon, day, hrs, min, sec;
+	unsigned char save_control;
+	unsigned int yrs;
+	unsigned long flags;
+
+	yrs = tm->tm_year + 1900;
+	mon = tm->tm_mon + 1;   /* tm_mon starts at zero */
+	day = tm->tm_mday;
+	hrs = tm->tm_hour;
+	min = tm->tm_min;
+	sec = tm->tm_sec;
+
+	if (yrs < 1970)
+		return -EINVAL;
+
+	yrs -= 1940;
+	if (yrs > 255)    /* They are unsigned */
+		return -EINVAL;
+
+	if (yrs >= 100)
+		yrs -= 100;
+
+	sec = bin2bcd(sec);
+	min = bin2bcd(min);
+	hrs = bin2bcd(hrs);
+	day = bin2bcd(day);
+	mon = bin2bcd(mon);
+	yrs = bin2bcd(yrs);
+
+	spin_lock_irqsave(&priv->lock, flags);
+	save_control = ds1286_rtc_read(priv, RTC_CMD);
+	ds1286_rtc_write(priv, (save_control|RTC_TE), RTC_CMD);
+
+	ds1286_rtc_write(priv, yrs, RTC_YEAR);
+	ds1286_rtc_write(priv, mon, RTC_MONTH);
+	ds1286_rtc_write(priv, day, RTC_DATE);
+	ds1286_rtc_write(priv, hrs, RTC_HOURS);
+	ds1286_rtc_write(priv, min, RTC_MINUTES);
+	ds1286_rtc_write(priv, sec, RTC_SECONDS);
+	ds1286_rtc_write(priv, 0, RTC_HUNDREDTH_SECOND);
+
+	ds1286_rtc_write(priv, save_control, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+	return 0;
+}
+
+static int ds1286_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	/*
+	 * Only the values that we read from the RTC are set. That
+	 * means only tm_wday, tm_hour, tm_min.
+	 */
+	spin_lock_irqsave(&priv->lock, flags);
+	alm->time.tm_min = ds1286_rtc_read(priv, RTC_MINUTES_ALARM) & 0x7f;
+	alm->time.tm_hour = ds1286_rtc_read(priv, RTC_HOURS_ALARM)  & 0x1f;
+	alm->time.tm_wday = ds1286_rtc_read(priv, RTC_DAY_ALARM)    & 0x07;
+	ds1286_rtc_read(priv, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	alm->time.tm_min = bcd2bin(alm->time.tm_min);
+	alm->time.tm_hour = bcd2bin(alm->time.tm_hour);
+	alm->time.tm_sec = 0;
+	return 0;
+}
+
+static int ds1286_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char hrs, min, sec;
+
+	hrs = alm->time.tm_hour;
+	min = alm->time.tm_min;
+	sec = alm->time.tm_sec;
+
+	if (hrs >= 24)
+		hrs = 0xff;
+
+	if (min >= 60)
+		min = 0xff;
+
+	if (sec != 0)
+		return -EINVAL;
+
+	min = bin2bcd(min);
+	hrs = bin2bcd(hrs);
+
+	spin_lock(&priv->lock);
+	ds1286_rtc_write(priv, hrs, RTC_HOURS_ALARM);
+	ds1286_rtc_write(priv, min, RTC_MINUTES_ALARM);
+	spin_unlock(&priv->lock);
+
+	return 0;
+}
+
+static const struct rtc_class_ops ds1286_ops = {
+	.ioctl		= ds1286_ioctl,
+	.proc		= ds1286_proc,
+	.read_time	= ds1286_read_time,
+	.set_time	= ds1286_set_time,
+	.read_alarm	= ds1286_read_alarm,
+	.set_alarm	= ds1286_set_alarm,
+	.alarm_irq_enable = ds1286_alarm_irq_enable,
+};
+
+static int ds1286_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+	struct ds1286_priv *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct ds1286_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->rtcregs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->rtcregs))
+		return PTR_ERR(priv->rtcregs);
+
+	spin_lock_init(&priv->lock);
+	platform_set_drvdata(pdev, priv);
+	rtc = devm_rtc_device_register(&pdev->dev, "ds1286", &ds1286_ops,
+					THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+	priv->rtc = rtc;
+	return 0;
+}
+
+static struct platform_driver ds1286_platform_driver = {
+	.driver		= {
+		.name	= "rtc-ds1286",
+	},
+	.probe		= ds1286_probe,
+};
+
+module_platform_driver(ds1286_platform_driver);
+
+MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
+MODULE_DESCRIPTION("DS1286 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:rtc-ds1286");