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, 322 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-lp8788.c b/drivers/rtc/rtc-lp8788.c
new file mode 100644
index 000000000..0793d7050
--- /dev/null
+++ b/drivers/rtc/rtc-lp8788.c
@@ -0,0 +1,322 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * TI LP8788 MFD - rtc driver
+ *
+ * Copyright 2012 Texas Instruments
+ *
+ * Author: Milo(Woogyom) Kim <milo.kim@ti.com>
+ */
+
+#include <linux/err.h>
+#include <linux/irqdomain.h>
+#include <linux/mfd/lp8788.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+/* register address */
+#define LP8788_INTEN_3			0x05
+#define LP8788_RTC_UNLOCK		0x64
+#define LP8788_RTC_SEC			0x70
+#define LP8788_ALM1_SEC			0x77
+#define LP8788_ALM1_EN			0x7D
+#define LP8788_ALM2_SEC			0x7E
+#define LP8788_ALM2_EN			0x84
+
+/* mask/shift bits */
+#define LP8788_INT_RTC_ALM1_M		BIT(1)	/* Addr 05h */
+#define LP8788_INT_RTC_ALM1_S		1
+#define LP8788_INT_RTC_ALM2_M		BIT(2)	/* Addr 05h */
+#define LP8788_INT_RTC_ALM2_S		2
+#define LP8788_ALM_EN_M			BIT(7)	/* Addr 7Dh or 84h */
+#define LP8788_ALM_EN_S			7
+
+#define DEFAULT_ALARM_SEL		LP8788_ALARM_1
+#define LP8788_MONTH_OFFSET		1
+#define LP8788_BASE_YEAR		2000
+#define MAX_WDAY_BITS			7
+#define LP8788_WDAY_SET			1
+#define RTC_UNLOCK			0x1
+#define RTC_LATCH			0x2
+#define ALARM_IRQ_FLAG			(RTC_IRQF | RTC_AF)
+
+enum lp8788_time {
+	LPTIME_SEC,
+	LPTIME_MIN,
+	LPTIME_HOUR,
+	LPTIME_MDAY,
+	LPTIME_MON,
+	LPTIME_YEAR,
+	LPTIME_WDAY,
+	LPTIME_MAX,
+};
+
+struct lp8788_rtc {
+	struct lp8788 *lp;
+	struct rtc_device *rdev;
+	enum lp8788_alarm_sel alarm;
+	int irq;
+};
+
+static const u8 addr_alarm_sec[LP8788_ALARM_MAX] = {
+	LP8788_ALM1_SEC,
+	LP8788_ALM2_SEC,
+};
+
+static const u8 addr_alarm_en[LP8788_ALARM_MAX] = {
+	LP8788_ALM1_EN,
+	LP8788_ALM2_EN,
+};
+
+static const u8 mask_alarm_en[LP8788_ALARM_MAX] = {
+	LP8788_INT_RTC_ALM1_M,
+	LP8788_INT_RTC_ALM2_M,
+};
+
+static const u8 shift_alarm_en[LP8788_ALARM_MAX] = {
+	LP8788_INT_RTC_ALM1_S,
+	LP8788_INT_RTC_ALM2_S,
+};
+
+static int _to_tm_wday(u8 lp8788_wday)
+{
+	int i;
+
+	if (lp8788_wday == 0)
+		return 0;
+
+	/* lookup defined weekday from read register value */
+	for (i = 0; i < MAX_WDAY_BITS; i++) {
+		if ((lp8788_wday >> i) == LP8788_WDAY_SET)
+			break;
+	}
+
+	return i + 1;
+}
+
+static inline int _to_lp8788_wday(int tm_wday)
+{
+	return LP8788_WDAY_SET << (tm_wday - 1);
+}
+
+static void lp8788_rtc_unlock(struct lp8788 *lp)
+{
+	lp8788_write_byte(lp, LP8788_RTC_UNLOCK, RTC_UNLOCK);
+	lp8788_write_byte(lp, LP8788_RTC_UNLOCK, RTC_LATCH);
+}
+
+static int lp8788_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct lp8788_rtc *rtc = dev_get_drvdata(dev);
+	struct lp8788 *lp = rtc->lp;
+	u8 data[LPTIME_MAX];
+	int ret;
+
+	lp8788_rtc_unlock(lp);
+
+	ret = lp8788_read_multi_bytes(lp, LP8788_RTC_SEC, data,	LPTIME_MAX);
+	if (ret)
+		return ret;
+
+	tm->tm_sec  = data[LPTIME_SEC];
+	tm->tm_min  = data[LPTIME_MIN];
+	tm->tm_hour = data[LPTIME_HOUR];
+	tm->tm_mday = data[LPTIME_MDAY];
+	tm->tm_mon  = data[LPTIME_MON] - LP8788_MONTH_OFFSET;
+	tm->tm_year = data[LPTIME_YEAR] + LP8788_BASE_YEAR - 1900;
+	tm->tm_wday = _to_tm_wday(data[LPTIME_WDAY]);
+
+	return 0;
+}
+
+static int lp8788_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct lp8788_rtc *rtc = dev_get_drvdata(dev);
+	struct lp8788 *lp = rtc->lp;
+	u8 data[LPTIME_MAX - 1];
+	int ret, i, year;
+
+	year = tm->tm_year + 1900 - LP8788_BASE_YEAR;
+	if (year < 0) {
+		dev_err(lp->dev, "invalid year: %d\n", year);
+		return -EINVAL;
+	}
+
+	/* because rtc weekday is a readonly register, do not update */
+	data[LPTIME_SEC]  = tm->tm_sec;
+	data[LPTIME_MIN]  = tm->tm_min;
+	data[LPTIME_HOUR] = tm->tm_hour;
+	data[LPTIME_MDAY] = tm->tm_mday;
+	data[LPTIME_MON]  = tm->tm_mon + LP8788_MONTH_OFFSET;
+	data[LPTIME_YEAR] = year;
+
+	for (i = 0; i < ARRAY_SIZE(data); i++) {
+		ret = lp8788_write_byte(lp, LP8788_RTC_SEC + i, data[i]);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static int lp8788_read_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct lp8788_rtc *rtc = dev_get_drvdata(dev);
+	struct lp8788 *lp = rtc->lp;
+	struct rtc_time *tm = &alarm->time;
+	u8 addr, data[LPTIME_MAX];
+	int ret;
+
+	addr = addr_alarm_sec[rtc->alarm];
+	ret = lp8788_read_multi_bytes(lp, addr, data, LPTIME_MAX);
+	if (ret)
+		return ret;
+
+	tm->tm_sec  = data[LPTIME_SEC];
+	tm->tm_min  = data[LPTIME_MIN];
+	tm->tm_hour = data[LPTIME_HOUR];
+	tm->tm_mday = data[LPTIME_MDAY];
+	tm->tm_mon  = data[LPTIME_MON] - LP8788_MONTH_OFFSET;
+	tm->tm_year = data[LPTIME_YEAR] + LP8788_BASE_YEAR - 1900;
+	tm->tm_wday = _to_tm_wday(data[LPTIME_WDAY]);
+	alarm->enabled = data[LPTIME_WDAY] & LP8788_ALM_EN_M;
+
+	return 0;
+}
+
+static int lp8788_set_alarm(struct device *dev, struct rtc_wkalrm *alarm)
+{
+	struct lp8788_rtc *rtc = dev_get_drvdata(dev);
+	struct lp8788 *lp = rtc->lp;
+	struct rtc_time *tm = &alarm->time;
+	u8 addr, data[LPTIME_MAX];
+	int ret, i, year;
+
+	year = tm->tm_year + 1900 - LP8788_BASE_YEAR;
+	if (year < 0) {
+		dev_err(lp->dev, "invalid year: %d\n", year);
+		return -EINVAL;
+	}
+
+	data[LPTIME_SEC]  = tm->tm_sec;
+	data[LPTIME_MIN]  = tm->tm_min;
+	data[LPTIME_HOUR] = tm->tm_hour;
+	data[LPTIME_MDAY] = tm->tm_mday;
+	data[LPTIME_MON]  = tm->tm_mon + LP8788_MONTH_OFFSET;
+	data[LPTIME_YEAR] = year;
+	data[LPTIME_WDAY] = _to_lp8788_wday(tm->tm_wday);
+
+	for (i = 0; i < ARRAY_SIZE(data); i++) {
+		addr = addr_alarm_sec[rtc->alarm] + i;
+		ret = lp8788_write_byte(lp, addr, data[i]);
+		if (ret)
+			return ret;
+	}
+
+	alarm->enabled = 1;
+	addr = addr_alarm_en[rtc->alarm];
+
+	return lp8788_update_bits(lp, addr, LP8788_ALM_EN_M,
+				alarm->enabled << LP8788_ALM_EN_S);
+}
+
+static int lp8788_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	struct lp8788_rtc *rtc = dev_get_drvdata(dev);
+	struct lp8788 *lp = rtc->lp;
+	u8 mask, shift;
+
+	if (!rtc->irq)
+		return -EIO;
+
+	mask = mask_alarm_en[rtc->alarm];
+	shift = shift_alarm_en[rtc->alarm];
+
+	return lp8788_update_bits(lp, LP8788_INTEN_3, mask, enable << shift);
+}
+
+static const struct rtc_class_ops lp8788_rtc_ops = {
+	.read_time = lp8788_rtc_read_time,
+	.set_time = lp8788_rtc_set_time,
+	.read_alarm = lp8788_read_alarm,
+	.set_alarm = lp8788_set_alarm,
+	.alarm_irq_enable = lp8788_alarm_irq_enable,
+};
+
+static irqreturn_t lp8788_alarm_irq_handler(int irq, void *ptr)
+{
+	struct lp8788_rtc *rtc = ptr;
+
+	rtc_update_irq(rtc->rdev, 1, ALARM_IRQ_FLAG);
+	return IRQ_HANDLED;
+}
+
+static int lp8788_alarm_irq_register(struct platform_device *pdev,
+				struct lp8788_rtc *rtc)
+{
+	struct resource *r;
+	struct lp8788 *lp = rtc->lp;
+	struct irq_domain *irqdm = lp->irqdm;
+	int irq;
+
+	rtc->irq = 0;
+
+	/* even the alarm IRQ number is not specified, rtc time should work */
+	r = platform_get_resource_byname(pdev, IORESOURCE_IRQ, LP8788_ALM_IRQ);
+	if (!r)
+		return 0;
+
+	if (rtc->alarm == LP8788_ALARM_1)
+		irq = r->start;
+	else
+		irq = r->end;
+
+	rtc->irq = irq_create_mapping(irqdm, irq);
+
+	return devm_request_threaded_irq(&pdev->dev, rtc->irq, NULL,
+				lp8788_alarm_irq_handler,
+				0, LP8788_ALM_IRQ, rtc);
+}
+
+static int lp8788_rtc_probe(struct platform_device *pdev)
+{
+	struct lp8788 *lp = dev_get_drvdata(pdev->dev.parent);
+	struct lp8788_rtc *rtc;
+	struct device *dev = &pdev->dev;
+
+	rtc = devm_kzalloc(dev, sizeof(struct lp8788_rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->lp = lp;
+	rtc->alarm = lp->pdata ? lp->pdata->alarm_sel : DEFAULT_ALARM_SEL;
+	platform_set_drvdata(pdev, rtc);
+
+	device_init_wakeup(dev, true);
+
+	rtc->rdev = devm_rtc_device_register(dev, "lp8788_rtc",
+					&lp8788_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc->rdev)) {
+		dev_err(dev, "can not register rtc device\n");
+		return PTR_ERR(rtc->rdev);
+	}
+
+	if (lp8788_alarm_irq_register(pdev, rtc))
+		dev_warn(lp->dev, "no rtc irq handler\n");
+
+	return 0;
+}
+
+static struct platform_driver lp8788_rtc_driver = {
+	.probe = lp8788_rtc_probe,
+	.driver = {
+		.name = LP8788_DEV_RTC,
+	},
+};
+module_platform_driver(lp8788_rtc_driver);
+
+MODULE_DESCRIPTION("Texas Instruments LP8788 RTC Driver");
+MODULE_AUTHOR("Milo Kim");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:lp8788-rtc");