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, 297 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-lpc24xx.c b/drivers/rtc/rtc-lpc24xx.c
new file mode 100644
index 000000000..a1266986d
--- /dev/null
+++ b/drivers/rtc/rtc-lpc24xx.c
@@ -0,0 +1,297 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * RTC driver for NXP LPC178x/18xx/43xx Real-Time Clock (RTC)
+ *
+ * Copyright (C) 2011 NXP Semiconductors
+ * Copyright (C) 2015 Joachim Eastwood <manabian@gmail.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+/* LPC24xx RTC register offsets and bits */
+#define LPC24XX_ILR		0x00
+#define  LPC24XX_RTCCIF		BIT(0)
+#define  LPC24XX_RTCALF		BIT(1)
+#define LPC24XX_CTC		0x04
+#define LPC24XX_CCR		0x08
+#define  LPC24XX_CLKEN		BIT(0)
+#define  LPC178X_CCALEN		BIT(4)
+#define LPC24XX_CIIR		0x0c
+#define LPC24XX_AMR		0x10
+#define  LPC24XX_ALARM_DISABLE	0xff
+#define LPC24XX_CTIME0		0x14
+#define LPC24XX_CTIME1		0x18
+#define LPC24XX_CTIME2		0x1c
+#define LPC24XX_SEC		0x20
+#define LPC24XX_MIN		0x24
+#define LPC24XX_HOUR		0x28
+#define LPC24XX_DOM		0x2c
+#define LPC24XX_DOW		0x30
+#define LPC24XX_DOY		0x34
+#define LPC24XX_MONTH		0x38
+#define LPC24XX_YEAR		0x3c
+#define LPC24XX_ALSEC		0x60
+#define LPC24XX_ALMIN		0x64
+#define LPC24XX_ALHOUR		0x68
+#define LPC24XX_ALDOM		0x6c
+#define LPC24XX_ALDOW		0x70
+#define LPC24XX_ALDOY		0x74
+#define LPC24XX_ALMON		0x78
+#define LPC24XX_ALYEAR		0x7c
+
+/* Macros to read fields in consolidated time (CT) registers */
+#define CT0_SECS(x)		(((x) >> 0)  & 0x3f)
+#define CT0_MINS(x)		(((x) >> 8)  & 0x3f)
+#define CT0_HOURS(x)		(((x) >> 16) & 0x1f)
+#define CT0_DOW(x)		(((x) >> 24) & 0x07)
+#define CT1_DOM(x)		(((x) >> 0)  & 0x1f)
+#define CT1_MONTH(x)		(((x) >> 8)  & 0x0f)
+#define CT1_YEAR(x)		(((x) >> 16) & 0xfff)
+#define CT2_DOY(x)		(((x) >> 0)  & 0xfff)
+
+#define rtc_readl(dev, reg)		readl((dev)->rtc_base + (reg))
+#define rtc_writel(dev, reg, val)	writel((val), (dev)->rtc_base + (reg))
+
+struct lpc24xx_rtc {
+	void __iomem *rtc_base;
+	struct rtc_device *rtc;
+	struct clk *clk_rtc;
+	struct clk *clk_reg;
+};
+
+static int lpc24xx_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
+
+	/* Disable RTC during update */
+	rtc_writel(rtc, LPC24XX_CCR, LPC178X_CCALEN);
+
+	rtc_writel(rtc, LPC24XX_SEC,	tm->tm_sec);
+	rtc_writel(rtc, LPC24XX_MIN,	tm->tm_min);
+	rtc_writel(rtc, LPC24XX_HOUR,	tm->tm_hour);
+	rtc_writel(rtc, LPC24XX_DOW,	tm->tm_wday);
+	rtc_writel(rtc, LPC24XX_DOM,	tm->tm_mday);
+	rtc_writel(rtc, LPC24XX_DOY,	tm->tm_yday);
+	rtc_writel(rtc, LPC24XX_MONTH,	tm->tm_mon);
+	rtc_writel(rtc, LPC24XX_YEAR,	tm->tm_year);
+
+	rtc_writel(rtc, LPC24XX_CCR, LPC24XX_CLKEN | LPC178X_CCALEN);
+
+	return 0;
+}
+
+static int lpc24xx_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
+	u32 ct0, ct1, ct2;
+
+	ct0 = rtc_readl(rtc, LPC24XX_CTIME0);
+	ct1 = rtc_readl(rtc, LPC24XX_CTIME1);
+	ct2 = rtc_readl(rtc, LPC24XX_CTIME2);
+
+	tm->tm_sec  = CT0_SECS(ct0);
+	tm->tm_min  = CT0_MINS(ct0);
+	tm->tm_hour = CT0_HOURS(ct0);
+	tm->tm_wday = CT0_DOW(ct0);
+	tm->tm_mon  = CT1_MONTH(ct1);
+	tm->tm_mday = CT1_DOM(ct1);
+	tm->tm_year = CT1_YEAR(ct1);
+	tm->tm_yday = CT2_DOY(ct2);
+
+	return 0;
+}
+
+static int lpc24xx_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
+{
+	struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time *tm = &wkalrm->time;
+
+	tm->tm_sec  = rtc_readl(rtc, LPC24XX_ALSEC);
+	tm->tm_min  = rtc_readl(rtc, LPC24XX_ALMIN);
+	tm->tm_hour = rtc_readl(rtc, LPC24XX_ALHOUR);
+	tm->tm_mday = rtc_readl(rtc, LPC24XX_ALDOM);
+	tm->tm_wday = rtc_readl(rtc, LPC24XX_ALDOW);
+	tm->tm_yday = rtc_readl(rtc, LPC24XX_ALDOY);
+	tm->tm_mon  = rtc_readl(rtc, LPC24XX_ALMON);
+	tm->tm_year = rtc_readl(rtc, LPC24XX_ALYEAR);
+
+	wkalrm->enabled = rtc_readl(rtc, LPC24XX_AMR) == 0;
+	wkalrm->pending = !!(rtc_readl(rtc, LPC24XX_ILR) & LPC24XX_RTCCIF);
+
+	return rtc_valid_tm(&wkalrm->time);
+}
+
+static int lpc24xx_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
+{
+	struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time *tm = &wkalrm->time;
+
+	/* Disable alarm irq during update */
+	rtc_writel(rtc, LPC24XX_AMR, LPC24XX_ALARM_DISABLE);
+
+	rtc_writel(rtc, LPC24XX_ALSEC,  tm->tm_sec);
+	rtc_writel(rtc, LPC24XX_ALMIN,  tm->tm_min);
+	rtc_writel(rtc, LPC24XX_ALHOUR, tm->tm_hour);
+	rtc_writel(rtc, LPC24XX_ALDOM,  tm->tm_mday);
+	rtc_writel(rtc, LPC24XX_ALDOW,  tm->tm_wday);
+	rtc_writel(rtc, LPC24XX_ALDOY,  tm->tm_yday);
+	rtc_writel(rtc, LPC24XX_ALMON,  tm->tm_mon);
+	rtc_writel(rtc, LPC24XX_ALYEAR, tm->tm_year);
+
+	if (wkalrm->enabled)
+		rtc_writel(rtc, LPC24XX_AMR, 0);
+
+	return 0;
+}
+
+static int lpc24xx_rtc_alarm_irq_enable(struct device *dev, unsigned int enable)
+{
+	struct lpc24xx_rtc *rtc = dev_get_drvdata(dev);
+
+	if (enable)
+		rtc_writel(rtc, LPC24XX_AMR, 0);
+	else
+		rtc_writel(rtc, LPC24XX_AMR, LPC24XX_ALARM_DISABLE);
+
+	return 0;
+}
+
+static irqreturn_t lpc24xx_rtc_interrupt(int irq, void *data)
+{
+	unsigned long events = RTC_IRQF;
+	struct lpc24xx_rtc *rtc = data;
+	u32 rtc_iir;
+
+	/* Check interrupt cause */
+	rtc_iir = rtc_readl(rtc, LPC24XX_ILR);
+	if (rtc_iir & LPC24XX_RTCALF) {
+		events |= RTC_AF;
+		rtc_writel(rtc, LPC24XX_AMR, LPC24XX_ALARM_DISABLE);
+	}
+
+	/* Clear interrupt status and report event */
+	rtc_writel(rtc, LPC24XX_ILR, rtc_iir);
+	rtc_update_irq(rtc->rtc, 1, events);
+
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops lpc24xx_rtc_ops = {
+	.read_time		= lpc24xx_rtc_read_time,
+	.set_time		= lpc24xx_rtc_set_time,
+	.read_alarm		= lpc24xx_rtc_read_alarm,
+	.set_alarm		= lpc24xx_rtc_set_alarm,
+	.alarm_irq_enable	= lpc24xx_rtc_alarm_irq_enable,
+};
+
+static int lpc24xx_rtc_probe(struct platform_device *pdev)
+{
+	struct lpc24xx_rtc *rtc;
+	int irq, ret;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(*rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->rtc_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rtc->rtc_base))
+		return PTR_ERR(rtc->rtc_base);
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	rtc->clk_rtc = devm_clk_get(&pdev->dev, "rtc");
+	if (IS_ERR(rtc->clk_rtc)) {
+		dev_err(&pdev->dev, "error getting rtc clock\n");
+		return PTR_ERR(rtc->clk_rtc);
+	}
+
+	rtc->clk_reg = devm_clk_get(&pdev->dev, "reg");
+	if (IS_ERR(rtc->clk_reg)) {
+		dev_err(&pdev->dev, "error getting reg clock\n");
+		return PTR_ERR(rtc->clk_reg);
+	}
+
+	ret = clk_prepare_enable(rtc->clk_rtc);
+	if (ret) {
+		dev_err(&pdev->dev, "unable to enable rtc clock\n");
+		return ret;
+	}
+
+	ret = clk_prepare_enable(rtc->clk_reg);
+	if (ret) {
+		dev_err(&pdev->dev, "unable to enable reg clock\n");
+		goto disable_rtc_clk;
+	}
+
+	platform_set_drvdata(pdev, rtc);
+
+	/* Clear any pending interrupts */
+	rtc_writel(rtc, LPC24XX_ILR, LPC24XX_RTCCIF | LPC24XX_RTCALF);
+
+	/* Enable RTC count */
+	rtc_writel(rtc, LPC24XX_CCR, LPC24XX_CLKEN | LPC178X_CCALEN);
+
+	ret = devm_request_irq(&pdev->dev, irq, lpc24xx_rtc_interrupt, 0,
+			       pdev->name, rtc);
+	if (ret < 0) {
+		dev_warn(&pdev->dev, "can't request interrupt\n");
+		goto disable_clks;
+	}
+
+	rtc->rtc = devm_rtc_device_register(&pdev->dev, "lpc24xx-rtc",
+					    &lpc24xx_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc->rtc)) {
+		dev_err(&pdev->dev, "can't register rtc device\n");
+		ret = PTR_ERR(rtc->rtc);
+		goto disable_clks;
+	}
+
+	return 0;
+
+disable_clks:
+	clk_disable_unprepare(rtc->clk_reg);
+disable_rtc_clk:
+	clk_disable_unprepare(rtc->clk_rtc);
+	return ret;
+}
+
+static void lpc24xx_rtc_remove(struct platform_device *pdev)
+{
+	struct lpc24xx_rtc *rtc = platform_get_drvdata(pdev);
+
+	/* Ensure all interrupt sources are masked */
+	rtc_writel(rtc, LPC24XX_AMR, LPC24XX_ALARM_DISABLE);
+	rtc_writel(rtc, LPC24XX_CIIR, 0);
+
+	rtc_writel(rtc, LPC24XX_CCR, LPC178X_CCALEN);
+
+	clk_disable_unprepare(rtc->clk_rtc);
+	clk_disable_unprepare(rtc->clk_reg);
+}
+
+static const struct of_device_id lpc24xx_rtc_match[] = {
+	{ .compatible = "nxp,lpc1788-rtc" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, lpc24xx_rtc_match);
+
+static struct platform_driver lpc24xx_rtc_driver = {
+	.probe	= lpc24xx_rtc_probe,
+	.remove = lpc24xx_rtc_remove,
+	.driver	= {
+		.name = "lpc24xx-rtc",
+		.of_match_table	= lpc24xx_rtc_match,
+	},
+};
+module_platform_driver(lpc24xx_rtc_driver);
+
+MODULE_AUTHOR("Kevin Wells <wellsk40@gmail.com>");
+MODULE_DESCRIPTION("RTC driver for the LPC178x/18xx/408x/43xx SoCs");
+MODULE_LICENSE("GPL");