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, 252 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-as3722.c b/drivers/rtc/rtc-as3722.c
new file mode 100644
index 000000000..9682d6457
--- /dev/null
+++ b/drivers/rtc/rtc-as3722.c
@@ -0,0 +1,252 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rtc-as3722.c - Real Time Clock driver for ams AS3722 PMICs
+ *
+ * Copyright (C) 2013 ams AG
+ * Copyright (c) 2013, NVIDIA Corporation. All rights reserved.
+ *
+ * Author: Florian Lobmaier <florian.lobmaier@ams.com>
+ * Author: Laxman Dewangan <ldewangan@nvidia.com>
+ */
+
+#include <linux/bcd.h>
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/ioctl.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mfd/as3722.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/time.h>
+
+#define AS3722_RTC_START_YEAR	  2000
+struct as3722_rtc {
+	struct rtc_device	*rtc;
+	struct device		*dev;
+	struct as3722		*as3722;
+	int			alarm_irq;
+	bool			irq_enable;
+};
+
+static void as3722_time_to_reg(u8 *rbuff, struct rtc_time *tm)
+{
+	rbuff[0] = bin2bcd(tm->tm_sec);
+	rbuff[1] = bin2bcd(tm->tm_min);
+	rbuff[2] = bin2bcd(tm->tm_hour);
+	rbuff[3] = bin2bcd(tm->tm_mday);
+	rbuff[4] = bin2bcd(tm->tm_mon + 1);
+	rbuff[5] = bin2bcd(tm->tm_year - (AS3722_RTC_START_YEAR - 1900));
+}
+
+static void as3722_reg_to_time(u8 *rbuff, struct rtc_time *tm)
+{
+	tm->tm_sec = bcd2bin(rbuff[0] & 0x7F);
+	tm->tm_min = bcd2bin(rbuff[1] & 0x7F);
+	tm->tm_hour = bcd2bin(rbuff[2] & 0x3F);
+	tm->tm_mday = bcd2bin(rbuff[3] & 0x3F);
+	tm->tm_mon = bcd2bin(rbuff[4] & 0x1F) - 1;
+	tm->tm_year = (AS3722_RTC_START_YEAR - 1900) + bcd2bin(rbuff[5] & 0x7F);
+	return;
+}
+
+static int as3722_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	ret = as3722_block_read(as3722, AS3722_RTC_SECOND_REG,
+			6, as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_SECOND reg block read failed %d\n", ret);
+		return ret;
+	}
+	as3722_reg_to_time(as_time_array, tm);
+	return 0;
+}
+
+static int as3722_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	if (tm->tm_year < (AS3722_RTC_START_YEAR - 1900))
+		return -EINVAL;
+
+	as3722_time_to_reg(as_time_array, tm);
+	ret = as3722_block_write(as3722, AS3722_RTC_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0)
+		dev_err(dev, "RTC_SECOND reg block write failed %d\n", ret);
+	return ret;
+}
+
+static int as3722_rtc_alarm_irq_enable(struct device *dev,
+		unsigned int enabled)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (enabled && !as3722_rtc->irq_enable) {
+		enable_irq(as3722_rtc->alarm_irq);
+		as3722_rtc->irq_enable = true;
+	} else if (!enabled && as3722_rtc->irq_enable)  {
+		disable_irq(as3722_rtc->alarm_irq);
+		as3722_rtc->irq_enable = false;
+	}
+	return 0;
+}
+
+static int as3722_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	ret = as3722_block_read(as3722, AS3722_RTC_ALARM_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_ALARM_SECOND block read failed %d\n", ret);
+		return ret;
+	}
+
+	as3722_reg_to_time(as_time_array, &alrm->time);
+	return 0;
+}
+
+static int as3722_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+	struct as3722 *as3722 = as3722_rtc->as3722;
+	u8 as_time_array[6];
+	int ret;
+
+	if (alrm->time.tm_year < (AS3722_RTC_START_YEAR - 1900))
+		return -EINVAL;
+
+	ret = as3722_rtc_alarm_irq_enable(dev, 0);
+	if (ret < 0) {
+		dev_err(dev, "Disable RTC alarm failed\n");
+		return ret;
+	}
+
+	as3722_time_to_reg(as_time_array, &alrm->time);
+	ret = as3722_block_write(as3722, AS3722_RTC_ALARM_SECOND_REG, 6,
+			as_time_array);
+	if (ret < 0) {
+		dev_err(dev, "RTC_ALARM_SECOND block write failed %d\n", ret);
+		return ret;
+	}
+
+	if (alrm->enabled)
+		ret = as3722_rtc_alarm_irq_enable(dev, alrm->enabled);
+	return ret;
+}
+
+static irqreturn_t as3722_alarm_irq(int irq, void *data)
+{
+	struct as3722_rtc *as3722_rtc = data;
+
+	rtc_update_irq(as3722_rtc->rtc, 1, RTC_IRQF | RTC_AF);
+	return IRQ_HANDLED;
+}
+
+static const struct rtc_class_ops as3722_rtc_ops = {
+	.read_time = as3722_rtc_read_time,
+	.set_time = as3722_rtc_set_time,
+	.read_alarm = as3722_rtc_read_alarm,
+	.set_alarm = as3722_rtc_set_alarm,
+	.alarm_irq_enable = as3722_rtc_alarm_irq_enable,
+};
+
+static int as3722_rtc_probe(struct platform_device *pdev)
+{
+	struct as3722 *as3722 = dev_get_drvdata(pdev->dev.parent);
+	struct as3722_rtc *as3722_rtc;
+	int ret;
+
+	as3722_rtc = devm_kzalloc(&pdev->dev, sizeof(*as3722_rtc), GFP_KERNEL);
+	if (!as3722_rtc)
+		return -ENOMEM;
+
+	as3722_rtc->as3722 = as3722;
+	as3722_rtc->dev = &pdev->dev;
+	platform_set_drvdata(pdev, as3722_rtc);
+
+	/* Enable the RTC to make sure it is running. */
+	ret = as3722_update_bits(as3722, AS3722_RTC_CONTROL_REG,
+			AS3722_RTC_ON | AS3722_RTC_ALARM_WAKEUP_EN,
+			AS3722_RTC_ON | AS3722_RTC_ALARM_WAKEUP_EN);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "RTC_CONTROL reg write failed: %d\n", ret);
+		return ret;
+	}
+
+	device_init_wakeup(&pdev->dev, true);
+
+	as3722_rtc->rtc = devm_rtc_device_register(&pdev->dev, "as3722-rtc",
+				&as3722_rtc_ops, THIS_MODULE);
+	if (IS_ERR(as3722_rtc->rtc)) {
+		ret = PTR_ERR(as3722_rtc->rtc);
+		dev_err(&pdev->dev, "RTC register failed: %d\n", ret);
+		return ret;
+	}
+
+	as3722_rtc->alarm_irq = platform_get_irq(pdev, 0);
+	dev_info(&pdev->dev, "RTC interrupt %d\n", as3722_rtc->alarm_irq);
+
+	ret = devm_request_threaded_irq(&pdev->dev, as3722_rtc->alarm_irq, NULL,
+			as3722_alarm_irq, IRQF_ONESHOT,
+			"rtc-alarm", as3722_rtc);
+	if (ret < 0) {
+		dev_err(&pdev->dev, "Failed to request alarm IRQ %d: %d\n",
+				as3722_rtc->alarm_irq, ret);
+		return ret;
+	}
+	disable_irq(as3722_rtc->alarm_irq);
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int as3722_rtc_suspend(struct device *dev)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		enable_irq_wake(as3722_rtc->alarm_irq);
+
+	return 0;
+}
+
+static int as3722_rtc_resume(struct device *dev)
+{
+	struct as3722_rtc *as3722_rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(as3722_rtc->alarm_irq);
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(as3722_rtc_pm_ops, as3722_rtc_suspend,
+			 as3722_rtc_resume);
+
+static struct platform_driver as3722_rtc_driver = {
+	.probe = as3722_rtc_probe,
+	.driver = {
+		.name = "as3722-rtc",
+		.pm = &as3722_rtc_pm_ops,
+	},
+};
+module_platform_driver(as3722_rtc_driver);
+
+MODULE_DESCRIPTION("RTC driver for AS3722 PMICs");
+MODULE_ALIAS("platform:as3722-rtc");
+MODULE_AUTHOR("Florian Lobmaier <florian.lobmaier@ams.com>");
+MODULE_AUTHOR("Laxman Dewangan <ldewangan@nvidia.com>");
+MODULE_LICENSE("GPL");