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, 408 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-mpc5121.c b/drivers/rtc/rtc-mpc5121.c
new file mode 100644
index 000000000..b90f8337a
--- /dev/null
+++ b/drivers/rtc/rtc-mpc5121.c
@@ -0,0 +1,408 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Real-time clock driver for MPC5121
+ *
+ * Copyright 2007, Domen Puncer <domen.puncer@telargo.com>
+ * Copyright 2008, Freescale Semiconductor, Inc. All rights reserved.
+ * Copyright 2011, Dmitry Eremin-Solenikov
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/of.h>
+#include <linux/of_irq.h>
+#include <linux/platform_device.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+
+struct mpc5121_rtc_regs {
+	u8 set_time;		/* RTC + 0x00 */
+	u8 hour_set;		/* RTC + 0x01 */
+	u8 minute_set;		/* RTC + 0x02 */
+	u8 second_set;		/* RTC + 0x03 */
+
+	u8 set_date;		/* RTC + 0x04 */
+	u8 month_set;		/* RTC + 0x05 */
+	u8 weekday_set;		/* RTC + 0x06 */
+	u8 date_set;		/* RTC + 0x07 */
+
+	u8 write_sw;		/* RTC + 0x08 */
+	u8 sw_set;		/* RTC + 0x09 */
+	u16 year_set;		/* RTC + 0x0a */
+
+	u8 alm_enable;		/* RTC + 0x0c */
+	u8 alm_hour_set;	/* RTC + 0x0d */
+	u8 alm_min_set;		/* RTC + 0x0e */
+	u8 int_enable;		/* RTC + 0x0f */
+
+	u8 reserved1;
+	u8 hour;		/* RTC + 0x11 */
+	u8 minute;		/* RTC + 0x12 */
+	u8 second;		/* RTC + 0x13 */
+
+	u8 month;		/* RTC + 0x14 */
+	u8 wday_mday;		/* RTC + 0x15 */
+	u16 year;		/* RTC + 0x16 */
+
+	u8 int_alm;		/* RTC + 0x18 */
+	u8 int_sw;		/* RTC + 0x19 */
+	u8 alm_status;		/* RTC + 0x1a */
+	u8 sw_minute;		/* RTC + 0x1b */
+
+	u8 bus_error_1;		/* RTC + 0x1c */
+	u8 int_day;		/* RTC + 0x1d */
+	u8 int_min;		/* RTC + 0x1e */
+	u8 int_sec;		/* RTC + 0x1f */
+
+	/*
+	 * target_time:
+	 *	intended to be used for hibernation but hibernation
+	 *	does not work on silicon rev 1.5 so use it for non-volatile
+	 *	storage of offset between the actual_time register and linux
+	 *	time
+	 */
+	u32 target_time;	/* RTC + 0x20 */
+	/*
+	 * actual_time:
+	 *	readonly time since VBAT_RTC was last connected
+	 */
+	u32 actual_time;	/* RTC + 0x24 */
+	u32 keep_alive;		/* RTC + 0x28 */
+};
+
+struct mpc5121_rtc_data {
+	unsigned irq;
+	unsigned irq_periodic;
+	struct mpc5121_rtc_regs __iomem *regs;
+	struct rtc_device *rtc;
+	struct rtc_wkalrm wkalarm;
+};
+
+/*
+ * Update second/minute/hour registers.
+ *
+ * This is just so alarm will work.
+ */
+static void mpc5121_rtc_update_smh(struct mpc5121_rtc_regs __iomem *regs,
+				   struct rtc_time *tm)
+{
+	out_8(&regs->second_set, tm->tm_sec);
+	out_8(&regs->minute_set, tm->tm_min);
+	out_8(&regs->hour_set, tm->tm_hour);
+
+	/* set time sequence */
+	out_8(&regs->set_time, 0x1);
+	out_8(&regs->set_time, 0x3);
+	out_8(&regs->set_time, 0x1);
+	out_8(&regs->set_time, 0x0);
+}
+
+static int mpc5121_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+	unsigned long now;
+
+	/*
+	 * linux time is actual_time plus the offset saved in target_time
+	 */
+	now = in_be32(&regs->actual_time) + in_be32(&regs->target_time);
+
+	rtc_time64_to_tm(now, tm);
+
+	/*
+	 * update second minute hour registers
+	 * so alarms will work
+	 */
+	mpc5121_rtc_update_smh(regs, tm);
+
+	return 0;
+}
+
+static int mpc5121_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+	unsigned long now;
+
+	/*
+	 * The actual_time register is read only so we write the offset
+	 * between it and linux time to the target_time register.
+	 */
+	now = rtc_tm_to_time64(tm);
+	out_be32(&regs->target_time, now - in_be32(&regs->actual_time));
+
+	/*
+	 * update second minute hour registers
+	 * so alarms will work
+	 */
+	mpc5121_rtc_update_smh(regs, tm);
+
+	return 0;
+}
+
+static int mpc5200_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+	int tmp;
+
+	tm->tm_sec = in_8(&regs->second);
+	tm->tm_min = in_8(&regs->minute);
+
+	/* 12 hour format? */
+	if (in_8(&regs->hour) & 0x20)
+		tm->tm_hour = (in_8(&regs->hour) >> 1) +
+			(in_8(&regs->hour) & 1 ? 12 : 0);
+	else
+		tm->tm_hour = in_8(&regs->hour);
+
+	tmp = in_8(&regs->wday_mday);
+	tm->tm_mday = tmp & 0x1f;
+	tm->tm_mon = in_8(&regs->month) - 1;
+	tm->tm_year = in_be16(&regs->year) - 1900;
+	tm->tm_wday = (tmp >> 5) % 7;
+	tm->tm_yday = rtc_year_days(tm->tm_mday, tm->tm_mon, tm->tm_year);
+	tm->tm_isdst = 0;
+
+	return 0;
+}
+
+static int mpc5200_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	mpc5121_rtc_update_smh(regs, tm);
+
+	/* date */
+	out_8(&regs->month_set, tm->tm_mon + 1);
+	out_8(&regs->weekday_set, tm->tm_wday ? tm->tm_wday : 7);
+	out_8(&regs->date_set, tm->tm_mday);
+	out_be16(&regs->year_set, tm->tm_year + 1900);
+
+	/* set date sequence */
+	out_8(&regs->set_date, 0x1);
+	out_8(&regs->set_date, 0x3);
+	out_8(&regs->set_date, 0x1);
+	out_8(&regs->set_date, 0x0);
+
+	return 0;
+}
+
+static int mpc5121_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	*alarm = rtc->wkalarm;
+
+	alarm->pending = in_8(&regs->alm_status);
+
+	return 0;
+}
+
+static int mpc5121_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	alarm->time.tm_mday = -1;
+	alarm->time.tm_mon = -1;
+	alarm->time.tm_year = -1;
+
+	out_8(&regs->alm_min_set, alarm->time.tm_min);
+	out_8(&regs->alm_hour_set, alarm->time.tm_hour);
+
+	out_8(&regs->alm_enable, alarm->enabled);
+
+	rtc->wkalarm = *alarm;
+	return 0;
+}
+
+static irqreturn_t mpc5121_rtc_handler(int irq, void *dev)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata((struct device *)dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	if (in_8(&regs->int_alm)) {
+		/* acknowledge and clear status */
+		out_8(&regs->int_alm, 1);
+		out_8(&regs->alm_status, 1);
+
+		rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_AF);
+		return IRQ_HANDLED;
+	}
+
+	return IRQ_NONE;
+}
+
+static irqreturn_t mpc5121_rtc_handler_upd(int irq, void *dev)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata((struct device *)dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	if (in_8(&regs->int_sec) && (in_8(&regs->int_enable) & 0x1)) {
+		/* acknowledge */
+		out_8(&regs->int_sec, 1);
+
+		rtc_update_irq(rtc->rtc, 1, RTC_IRQF | RTC_UF);
+		return IRQ_HANDLED;
+	}
+
+	return IRQ_NONE;
+}
+
+static int mpc5121_rtc_alarm_irq_enable(struct device *dev,
+					unsigned int enabled)
+{
+	struct mpc5121_rtc_data *rtc = dev_get_drvdata(dev);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+	int val;
+
+	if (enabled)
+		val = 1;
+	else
+		val = 0;
+
+	out_8(&regs->alm_enable, val);
+	rtc->wkalarm.enabled = val;
+
+	return 0;
+}
+
+static const struct rtc_class_ops mpc5121_rtc_ops = {
+	.read_time = mpc5121_rtc_read_time,
+	.set_time = mpc5121_rtc_set_time,
+	.read_alarm = mpc5121_rtc_read_alarm,
+	.set_alarm = mpc5121_rtc_set_alarm,
+	.alarm_irq_enable = mpc5121_rtc_alarm_irq_enable,
+};
+
+static const struct rtc_class_ops mpc5200_rtc_ops = {
+	.read_time = mpc5200_rtc_read_time,
+	.set_time = mpc5200_rtc_set_time,
+	.read_alarm = mpc5121_rtc_read_alarm,
+	.set_alarm = mpc5121_rtc_set_alarm,
+	.alarm_irq_enable = mpc5121_rtc_alarm_irq_enable,
+};
+
+static int mpc5121_rtc_probe(struct platform_device *op)
+{
+	struct mpc5121_rtc_data *rtc;
+	int err = 0;
+
+	rtc = devm_kzalloc(&op->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->regs = devm_platform_ioremap_resource(op, 0);
+	if (IS_ERR(rtc->regs)) {
+		dev_err(&op->dev, "%s: couldn't map io space\n", __func__);
+		return PTR_ERR(rtc->regs);
+	}
+
+	device_init_wakeup(&op->dev, true);
+
+	platform_set_drvdata(op, rtc);
+
+	rtc->irq = irq_of_parse_and_map(op->dev.of_node, 1);
+	err = devm_request_irq(&op->dev, rtc->irq, mpc5121_rtc_handler, 0,
+			       "mpc5121-rtc", &op->dev);
+	if (err) {
+		dev_err(&op->dev, "%s: could not request irq: %i\n",
+							__func__, rtc->irq);
+		goto out_dispose;
+	}
+
+	rtc->irq_periodic = irq_of_parse_and_map(op->dev.of_node, 0);
+	err = devm_request_irq(&op->dev, rtc->irq_periodic,
+			       mpc5121_rtc_handler_upd, 0, "mpc5121-rtc_upd",
+			       &op->dev);
+	if (err) {
+		dev_err(&op->dev, "%s: could not request irq: %i\n",
+						__func__, rtc->irq_periodic);
+		goto out_dispose2;
+	}
+
+	rtc->rtc = devm_rtc_allocate_device(&op->dev);
+	if (IS_ERR(rtc->rtc)) {
+		err = PTR_ERR(rtc->rtc);
+		goto out_dispose2;
+	}
+
+	rtc->rtc->ops = &mpc5200_rtc_ops;
+	set_bit(RTC_FEATURE_ALARM_RES_MINUTE, rtc->rtc->features);
+	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, rtc->rtc->features);
+	rtc->rtc->range_min = RTC_TIMESTAMP_BEGIN_0000;
+	rtc->rtc->range_max = 65733206399ULL; /* 4052-12-31 23:59:59 */
+
+	if (of_device_is_compatible(op->dev.of_node, "fsl,mpc5121-rtc")) {
+		u32 ka;
+		ka = in_be32(&rtc->regs->keep_alive);
+		if (ka & 0x02) {
+			dev_warn(&op->dev,
+				"mpc5121-rtc: Battery or oscillator failure!\n");
+			out_be32(&rtc->regs->keep_alive, ka);
+		}
+		rtc->rtc->ops = &mpc5121_rtc_ops;
+		/*
+		 * This is a limitation of the driver that abuses the target
+		 * time register, the actual maximum year for the mpc5121 is
+		 * also 4052.
+		 */
+		rtc->rtc->range_min = 0;
+		rtc->rtc->range_max = U32_MAX;
+	}
+
+	err = devm_rtc_register_device(rtc->rtc);
+	if (err)
+		goto out_dispose2;
+
+	return 0;
+
+out_dispose2:
+	irq_dispose_mapping(rtc->irq_periodic);
+out_dispose:
+	irq_dispose_mapping(rtc->irq);
+
+	return err;
+}
+
+static void mpc5121_rtc_remove(struct platform_device *op)
+{
+	struct mpc5121_rtc_data *rtc = platform_get_drvdata(op);
+	struct mpc5121_rtc_regs __iomem *regs = rtc->regs;
+
+	/* disable interrupt, so there are no nasty surprises */
+	out_8(&regs->alm_enable, 0);
+	out_8(&regs->int_enable, in_8(&regs->int_enable) & ~0x1);
+
+	irq_dispose_mapping(rtc->irq);
+	irq_dispose_mapping(rtc->irq_periodic);
+}
+
+#ifdef CONFIG_OF
+static const struct of_device_id mpc5121_rtc_match[] = {
+	{ .compatible = "fsl,mpc5121-rtc", },
+	{ .compatible = "fsl,mpc5200-rtc", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mpc5121_rtc_match);
+#endif
+
+static struct platform_driver mpc5121_rtc_driver = {
+	.driver = {
+		.name = "mpc5121-rtc",
+		.of_match_table = of_match_ptr(mpc5121_rtc_match),
+	},
+	.probe = mpc5121_rtc_probe,
+	.remove = mpc5121_rtc_remove,
+};
+
+module_platform_driver(mpc5121_rtc_driver);
+
+MODULE_DESCRIPTION("Freescale MPC5121 built-in RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("John Rigby <jcrigby@gmail.com>");