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, 307 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-moxart.c b/drivers/rtc/rtc-moxart.c
new file mode 100644
index 000000000..bc0345db6
--- /dev/null
+++ b/drivers/rtc/rtc-moxart.c
@@ -0,0 +1,307 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * MOXA ART RTC driver.
+ *
+ * Copyright (C) 2013 Jonas Jensen
+ *
+ * Jonas Jensen <jonas.jensen@gmail.com>
+ *
+ * Based on code from
+ * Moxa Technology Co., Ltd. <www.moxa.com>
+ */
+
+#include <linux/err.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/module.h>
+#include <linux/gpio/consumer.h>
+
+#define GPIO_RTC_RESERVED			0x0C
+#define GPIO_RTC_DATA_SET			0x10
+#define GPIO_RTC_DATA_CLEAR			0x14
+#define GPIO_RTC_PIN_PULL_ENABLE		0x18
+#define GPIO_RTC_PIN_PULL_TYPE			0x1C
+#define GPIO_RTC_INT_ENABLE			0x20
+#define GPIO_RTC_INT_RAW_STATE			0x24
+#define GPIO_RTC_INT_MASKED_STATE		0x28
+#define GPIO_RTC_INT_MASK			0x2C
+#define GPIO_RTC_INT_CLEAR			0x30
+#define GPIO_RTC_INT_TRIGGER			0x34
+#define GPIO_RTC_INT_BOTH			0x38
+#define GPIO_RTC_INT_RISE_NEG			0x3C
+#define GPIO_RTC_BOUNCE_ENABLE			0x40
+#define GPIO_RTC_BOUNCE_PRE_SCALE		0x44
+#define GPIO_RTC_PROTECT_W			0x8E
+#define GPIO_RTC_PROTECT_R			0x8F
+#define GPIO_RTC_YEAR_W				0x8C
+#define GPIO_RTC_YEAR_R				0x8D
+#define GPIO_RTC_DAY_W				0x8A
+#define GPIO_RTC_DAY_R				0x8B
+#define GPIO_RTC_MONTH_W			0x88
+#define GPIO_RTC_MONTH_R			0x89
+#define GPIO_RTC_DATE_W				0x86
+#define GPIO_RTC_DATE_R				0x87
+#define GPIO_RTC_HOURS_W			0x84
+#define GPIO_RTC_HOURS_R			0x85
+#define GPIO_RTC_MINUTES_W			0x82
+#define GPIO_RTC_MINUTES_R			0x83
+#define GPIO_RTC_SECONDS_W			0x80
+#define GPIO_RTC_SECONDS_R			0x81
+#define GPIO_RTC_DELAY_TIME			8
+
+struct moxart_rtc {
+	struct rtc_device *rtc;
+	spinlock_t rtc_lock;
+	struct gpio_desc *gpio_data;
+	struct gpio_desc *gpio_sclk;
+	struct gpio_desc *gpio_reset;
+};
+
+static int day_of_year[12] =	{ 0, 31, 59, 90, 120, 151, 181,
+				  212, 243, 273, 304, 334 };
+
+static void moxart_rtc_write_byte(struct device *dev, u8 data)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+	int i;
+
+	for (i = 0; i < 8; i++, data >>= 1) {
+		gpiod_set_value(moxart_rtc->gpio_sclk, 0);
+		gpiod_set_value(moxart_rtc->gpio_data, ((data & 1) == 1));
+		udelay(GPIO_RTC_DELAY_TIME);
+		gpiod_set_value(moxart_rtc->gpio_sclk, 1);
+		udelay(GPIO_RTC_DELAY_TIME);
+	}
+}
+
+static u8 moxart_rtc_read_byte(struct device *dev)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+	int i;
+	u8 data = 0;
+
+	for (i = 0; i < 8; i++) {
+		gpiod_set_value(moxart_rtc->gpio_sclk, 0);
+		udelay(GPIO_RTC_DELAY_TIME);
+		gpiod_set_value(moxart_rtc->gpio_sclk, 1);
+		udelay(GPIO_RTC_DELAY_TIME);
+		if (gpiod_get_value(moxart_rtc->gpio_data))
+			data |= (1 << i);
+		udelay(GPIO_RTC_DELAY_TIME);
+	}
+	return data;
+}
+
+static u8 moxart_rtc_read_register(struct device *dev, u8 cmd)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+	u8 data;
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	gpiod_direction_output(moxart_rtc->gpio_data, 0);
+	gpiod_set_value(moxart_rtc->gpio_reset, 1);
+	udelay(GPIO_RTC_DELAY_TIME);
+	moxart_rtc_write_byte(dev, cmd);
+	gpiod_direction_input(moxart_rtc->gpio_data);
+	udelay(GPIO_RTC_DELAY_TIME);
+	data = moxart_rtc_read_byte(dev);
+	gpiod_set_value(moxart_rtc->gpio_sclk, 0);
+	gpiod_set_value(moxart_rtc->gpio_reset, 0);
+	udelay(GPIO_RTC_DELAY_TIME);
+
+	local_irq_restore(flags);
+
+	return data;
+}
+
+static void moxart_rtc_write_register(struct device *dev, u8 cmd, u8 data)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	local_irq_save(flags);
+
+	gpiod_direction_output(moxart_rtc->gpio_data, 0);
+	gpiod_set_value(moxart_rtc->gpio_reset, 1);
+	udelay(GPIO_RTC_DELAY_TIME);
+	moxart_rtc_write_byte(dev, cmd);
+	moxart_rtc_write_byte(dev, data);
+	gpiod_set_value(moxart_rtc->gpio_sclk, 0);
+	gpiod_set_value(moxart_rtc->gpio_reset, 0);
+	udelay(GPIO_RTC_DELAY_TIME);
+
+	local_irq_restore(flags);
+}
+
+static int moxart_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+
+	spin_lock_irq(&moxart_rtc->rtc_lock);
+
+	moxart_rtc_write_register(dev, GPIO_RTC_PROTECT_W, 0);
+	moxart_rtc_write_register(dev, GPIO_RTC_YEAR_W,
+				  (((tm->tm_year - 100) / 10) << 4) |
+				  ((tm->tm_year - 100) % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_MONTH_W,
+				  (((tm->tm_mon + 1) / 10) << 4) |
+				  ((tm->tm_mon + 1) % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_DATE_W,
+				  ((tm->tm_mday / 10) << 4) |
+				  (tm->tm_mday % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_HOURS_W,
+				  ((tm->tm_hour / 10) << 4) |
+				  (tm->tm_hour % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_MINUTES_W,
+				  ((tm->tm_min / 10) << 4) |
+				  (tm->tm_min % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_SECONDS_W,
+				  ((tm->tm_sec / 10) << 4) |
+				  (tm->tm_sec % 10));
+
+	moxart_rtc_write_register(dev, GPIO_RTC_PROTECT_W, 0x80);
+
+	spin_unlock_irq(&moxart_rtc->rtc_lock);
+
+	dev_dbg(dev, "%s: success tm_year=%d tm_mon=%d\n"
+		"tm_mday=%d tm_hour=%d tm_min=%d tm_sec=%d\n",
+		__func__, tm->tm_year, tm->tm_mon, tm->tm_mday,
+		tm->tm_hour, tm->tm_min, tm->tm_sec);
+
+	return 0;
+}
+
+static int moxart_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct moxart_rtc *moxart_rtc = dev_get_drvdata(dev);
+	unsigned char v;
+
+	spin_lock_irq(&moxart_rtc->rtc_lock);
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_SECONDS_R);
+	tm->tm_sec = (((v & 0x70) >> 4) * 10) + (v & 0x0F);
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_MINUTES_R);
+	tm->tm_min = (((v & 0x70) >> 4) * 10) + (v & 0x0F);
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_HOURS_R);
+	if (v & 0x80) { /* 12-hour mode */
+		tm->tm_hour = (((v & 0x10) >> 4) * 10) + (v & 0x0F);
+		if (v & 0x20) { /* PM mode */
+			tm->tm_hour += 12;
+			if (tm->tm_hour >= 24)
+				tm->tm_hour = 0;
+		}
+	} else { /* 24-hour mode */
+		tm->tm_hour = (((v & 0x30) >> 4) * 10) + (v & 0x0F);
+	}
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_DATE_R);
+	tm->tm_mday = (((v & 0x30) >> 4) * 10) + (v & 0x0F);
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_MONTH_R);
+	tm->tm_mon = (((v & 0x10) >> 4) * 10) + (v & 0x0F);
+	tm->tm_mon--;
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_YEAR_R);
+	tm->tm_year = (((v & 0xF0) >> 4) * 10) + (v & 0x0F);
+	tm->tm_year += 100;
+	if (tm->tm_year <= 69)
+		tm->tm_year += 100;
+
+	v = moxart_rtc_read_register(dev, GPIO_RTC_DAY_R);
+	tm->tm_wday = (v & 0x0f) - 1;
+	tm->tm_yday = day_of_year[tm->tm_mon];
+	tm->tm_yday += (tm->tm_mday - 1);
+	if (tm->tm_mon >= 2) {
+		if (!(tm->tm_year % 4) && (tm->tm_year % 100))
+			tm->tm_yday++;
+	}
+
+	tm->tm_isdst = 0;
+
+	spin_unlock_irq(&moxart_rtc->rtc_lock);
+
+	return 0;
+}
+
+static const struct rtc_class_ops moxart_rtc_ops = {
+	.read_time	= moxart_rtc_read_time,
+	.set_time	= moxart_rtc_set_time,
+};
+
+static int moxart_rtc_probe(struct platform_device *pdev)
+{
+	struct moxart_rtc *moxart_rtc;
+	int ret = 0;
+
+	moxart_rtc = devm_kzalloc(&pdev->dev, sizeof(*moxart_rtc), GFP_KERNEL);
+	if (!moxart_rtc)
+		return -ENOMEM;
+
+	moxart_rtc->gpio_data = devm_gpiod_get(&pdev->dev, "rtc-data",
+					       GPIOD_IN);
+	ret = PTR_ERR_OR_ZERO(moxart_rtc->gpio_data);
+	if (ret) {
+		dev_err(&pdev->dev, "can't get rtc data gpio: %d\n", ret);
+		return ret;
+	}
+
+	moxart_rtc->gpio_sclk = devm_gpiod_get(&pdev->dev, "rtc-sclk",
+					       GPIOD_ASIS);
+	ret = PTR_ERR_OR_ZERO(moxart_rtc->gpio_sclk);
+	if (ret) {
+		dev_err(&pdev->dev, "can't get rtc sclk gpio: %d\n", ret);
+		return ret;
+	}
+
+	moxart_rtc->gpio_reset = devm_gpiod_get(&pdev->dev, "rtc-reset",
+						GPIOD_ASIS);
+	ret = PTR_ERR_OR_ZERO(moxart_rtc->gpio_reset);
+	if (ret) {
+		dev_err(&pdev->dev, "can't get rtc reset gpio: %d\n", ret);
+		return ret;
+	}
+
+	spin_lock_init(&moxart_rtc->rtc_lock);
+	platform_set_drvdata(pdev, moxart_rtc);
+
+	moxart_rtc->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
+						   &moxart_rtc_ops,
+						   THIS_MODULE);
+	if (IS_ERR(moxart_rtc->rtc)) {
+		dev_err(&pdev->dev, "devm_rtc_device_register failed\n");
+		return PTR_ERR(moxart_rtc->rtc);
+	}
+
+	return 0;
+}
+
+static const struct of_device_id moxart_rtc_match[] = {
+	{ .compatible = "moxa,moxart-rtc" },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, moxart_rtc_match);
+
+static struct platform_driver moxart_rtc_driver = {
+	.probe	= moxart_rtc_probe,
+	.driver	= {
+		.name		= "moxart-rtc",
+		.of_match_table	= moxart_rtc_match,
+	},
+};
+module_platform_driver(moxart_rtc_driver);
+
+MODULE_DESCRIPTION("MOXART RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Jonas Jensen <jonas.jensen@gmail.com>");