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, 592 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-hym8563.c b/drivers/rtc/rtc-hym8563.c
new file mode 100644
index 000000000..3156aa5f2
--- /dev/null
+++ b/drivers/rtc/rtc-hym8563.c
@@ -0,0 +1,592 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Haoyu HYM8563 RTC driver
+ *
+ * Copyright (C) 2013 MundoReader S.L.
+ * Author: Heiko Stuebner <heiko@sntech.de>
+ *
+ * based on rtc-HYM8563
+ * Copyright (C) 2010 ROCKCHIP, Inc.
+ */
+
+#include <linux/module.h>
+#include <linux/clk-provider.h>
+#include <linux/i2c.h>
+#include <linux/bcd.h>
+#include <linux/rtc.h>
+
+#define HYM8563_CTL1		0x00
+#define HYM8563_CTL1_TEST	BIT(7)
+#define HYM8563_CTL1_STOP	BIT(5)
+#define HYM8563_CTL1_TESTC	BIT(3)
+
+#define HYM8563_CTL2		0x01
+#define HYM8563_CTL2_TI_TP	BIT(4)
+#define HYM8563_CTL2_AF		BIT(3)
+#define HYM8563_CTL2_TF		BIT(2)
+#define HYM8563_CTL2_AIE	BIT(1)
+#define HYM8563_CTL2_TIE	BIT(0)
+
+#define HYM8563_SEC		0x02
+#define HYM8563_SEC_VL		BIT(7)
+#define HYM8563_SEC_MASK	0x7f
+
+#define HYM8563_MIN		0x03
+#define HYM8563_MIN_MASK	0x7f
+
+#define HYM8563_HOUR		0x04
+#define HYM8563_HOUR_MASK	0x3f
+
+#define HYM8563_DAY		0x05
+#define HYM8563_DAY_MASK	0x3f
+
+#define HYM8563_WEEKDAY		0x06
+#define HYM8563_WEEKDAY_MASK	0x07
+
+#define HYM8563_MONTH		0x07
+#define HYM8563_MONTH_CENTURY	BIT(7)
+#define HYM8563_MONTH_MASK	0x1f
+
+#define HYM8563_YEAR		0x08
+
+#define HYM8563_ALM_MIN		0x09
+#define HYM8563_ALM_HOUR	0x0a
+#define HYM8563_ALM_DAY		0x0b
+#define HYM8563_ALM_WEEK	0x0c
+
+/* Each alarm check can be disabled by setting this bit in the register */
+#define HYM8563_ALM_BIT_DISABLE	BIT(7)
+
+#define HYM8563_CLKOUT		0x0d
+#define HYM8563_CLKOUT_ENABLE	BIT(7)
+#define HYM8563_CLKOUT_32768	0
+#define HYM8563_CLKOUT_1024	1
+#define HYM8563_CLKOUT_32	2
+#define HYM8563_CLKOUT_1	3
+#define HYM8563_CLKOUT_MASK	3
+
+#define HYM8563_TMR_CTL		0x0e
+#define HYM8563_TMR_CTL_ENABLE	BIT(7)
+#define HYM8563_TMR_CTL_4096	0
+#define HYM8563_TMR_CTL_64	1
+#define HYM8563_TMR_CTL_1	2
+#define HYM8563_TMR_CTL_1_60	3
+#define HYM8563_TMR_CTL_MASK	3
+
+#define HYM8563_TMR_CNT		0x0f
+
+struct hym8563 {
+	struct i2c_client	*client;
+	struct rtc_device	*rtc;
+#ifdef CONFIG_COMMON_CLK
+	struct clk_hw		clkout_hw;
+#endif
+};
+
+/*
+ * RTC handling
+ */
+
+static int hym8563_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	u8 buf[7];
+	int ret;
+
+	ret = i2c_smbus_read_i2c_block_data(client, HYM8563_SEC, 7, buf);
+	if (ret < 0)
+		return ret;
+
+	if (buf[0] & HYM8563_SEC_VL) {
+		dev_warn(&client->dev,
+			 "no valid clock/calendar values available\n");
+		return -EINVAL;
+	}
+
+	tm->tm_sec = bcd2bin(buf[0] & HYM8563_SEC_MASK);
+	tm->tm_min = bcd2bin(buf[1] & HYM8563_MIN_MASK);
+	tm->tm_hour = bcd2bin(buf[2] & HYM8563_HOUR_MASK);
+	tm->tm_mday = bcd2bin(buf[3] & HYM8563_DAY_MASK);
+	tm->tm_wday = bcd2bin(buf[4] & HYM8563_WEEKDAY_MASK); /* 0 = Sun */
+	tm->tm_mon = bcd2bin(buf[5] & HYM8563_MONTH_MASK) - 1; /* 0 = Jan */
+	tm->tm_year = bcd2bin(buf[6]) + 100;
+
+	return 0;
+}
+
+static int hym8563_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	u8 buf[7];
+	int ret;
+
+	/* Years >= 2100 are to far in the future, 19XX is to early */
+	if (tm->tm_year < 100 || tm->tm_year >= 200)
+		return -EINVAL;
+
+	buf[0] = bin2bcd(tm->tm_sec);
+	buf[1] = bin2bcd(tm->tm_min);
+	buf[2] = bin2bcd(tm->tm_hour);
+	buf[3] = bin2bcd(tm->tm_mday);
+	buf[4] = bin2bcd(tm->tm_wday);
+	buf[5] = bin2bcd(tm->tm_mon + 1);
+
+	/*
+	 * While the HYM8563 has a century flag in the month register,
+	 * it does not seem to carry it over a subsequent write/read.
+	 * So we'll limit ourself to 100 years, starting at 2000 for now.
+	 */
+	buf[6] = bin2bcd(tm->tm_year - 100);
+
+	/*
+	 * CTL1 only contains TEST-mode bits apart from stop,
+	 * so no need to read the value first
+	 */
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CTL1,
+						HYM8563_CTL1_STOP);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_i2c_block_data(client, HYM8563_SEC, 7, buf);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CTL1, 0);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static int hym8563_rtc_alarm_irq_enable(struct device *dev,
+					unsigned int enabled)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int data;
+
+	data = i2c_smbus_read_byte_data(client, HYM8563_CTL2);
+	if (data < 0)
+		return data;
+
+	if (enabled)
+		data |= HYM8563_CTL2_AIE;
+	else
+		data &= ~HYM8563_CTL2_AIE;
+
+	return i2c_smbus_write_byte_data(client, HYM8563_CTL2, data);
+};
+
+static int hym8563_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct rtc_time *alm_tm = &alm->time;
+	u8 buf[4];
+	int ret;
+
+	ret = i2c_smbus_read_i2c_block_data(client, HYM8563_ALM_MIN, 4, buf);
+	if (ret < 0)
+		return ret;
+
+	/* The alarm only has a minute accuracy */
+	alm_tm->tm_sec = 0;
+
+	alm_tm->tm_min = (buf[0] & HYM8563_ALM_BIT_DISABLE) ?
+					-1 :
+					bcd2bin(buf[0] & HYM8563_MIN_MASK);
+	alm_tm->tm_hour = (buf[1] & HYM8563_ALM_BIT_DISABLE) ?
+					-1 :
+					bcd2bin(buf[1] & HYM8563_HOUR_MASK);
+	alm_tm->tm_mday = (buf[2] & HYM8563_ALM_BIT_DISABLE) ?
+					-1 :
+					bcd2bin(buf[2] & HYM8563_DAY_MASK);
+	alm_tm->tm_wday = (buf[3] & HYM8563_ALM_BIT_DISABLE) ?
+					-1 :
+					bcd2bin(buf[3] & HYM8563_WEEKDAY_MASK);
+
+	ret = i2c_smbus_read_byte_data(client, HYM8563_CTL2);
+	if (ret < 0)
+		return ret;
+
+	if (ret & HYM8563_CTL2_AIE)
+		alm->enabled = 1;
+
+	return 0;
+}
+
+static int hym8563_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	struct rtc_time *alm_tm = &alm->time;
+	u8 buf[4];
+	int ret;
+
+	ret = i2c_smbus_read_byte_data(client, HYM8563_CTL2);
+	if (ret < 0)
+		return ret;
+
+	ret &= ~HYM8563_CTL2_AIE;
+
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CTL2, ret);
+	if (ret < 0)
+		return ret;
+
+	buf[0] = (alm_tm->tm_min < 60 && alm_tm->tm_min >= 0) ?
+			bin2bcd(alm_tm->tm_min) : HYM8563_ALM_BIT_DISABLE;
+
+	buf[1] = (alm_tm->tm_hour < 24 && alm_tm->tm_hour >= 0) ?
+			bin2bcd(alm_tm->tm_hour) : HYM8563_ALM_BIT_DISABLE;
+
+	buf[2] = (alm_tm->tm_mday <= 31 && alm_tm->tm_mday >= 1) ?
+			bin2bcd(alm_tm->tm_mday) : HYM8563_ALM_BIT_DISABLE;
+
+	buf[3] = (alm_tm->tm_wday < 7 && alm_tm->tm_wday >= 0) ?
+			bin2bcd(alm_tm->tm_wday) : HYM8563_ALM_BIT_DISABLE;
+
+	ret = i2c_smbus_write_i2c_block_data(client, HYM8563_ALM_MIN, 4, buf);
+	if (ret < 0)
+		return ret;
+
+	return hym8563_rtc_alarm_irq_enable(dev, alm->enabled);
+}
+
+static const struct rtc_class_ops hym8563_rtc_ops = {
+	.read_time		= hym8563_rtc_read_time,
+	.set_time		= hym8563_rtc_set_time,
+	.alarm_irq_enable	= hym8563_rtc_alarm_irq_enable,
+	.read_alarm		= hym8563_rtc_read_alarm,
+	.set_alarm		= hym8563_rtc_set_alarm,
+};
+
+/*
+ * Handling of the clkout
+ */
+
+#ifdef CONFIG_COMMON_CLK
+#define clkout_hw_to_hym8563(_hw) container_of(_hw, struct hym8563, clkout_hw)
+
+static int clkout_rates[] = {
+	32768,
+	1024,
+	32,
+	1,
+};
+
+static unsigned long hym8563_clkout_recalc_rate(struct clk_hw *hw,
+						unsigned long parent_rate)
+{
+	struct hym8563 *hym8563 = clkout_hw_to_hym8563(hw);
+	struct i2c_client *client = hym8563->client;
+	int ret = i2c_smbus_read_byte_data(client, HYM8563_CLKOUT);
+
+	if (ret < 0)
+		return 0;
+
+	ret &= HYM8563_CLKOUT_MASK;
+	return clkout_rates[ret];
+}
+
+static int hym8563_clkout_determine_rate(struct clk_hw *hw,
+					 struct clk_rate_request *req)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(clkout_rates); i++)
+		if (clkout_rates[i] <= req->rate) {
+			req->rate = clkout_rates[i];
+
+			return 0;
+		}
+
+	req->rate = clkout_rates[0];
+
+	return 0;
+}
+
+static int hym8563_clkout_set_rate(struct clk_hw *hw, unsigned long rate,
+				   unsigned long parent_rate)
+{
+	struct hym8563 *hym8563 = clkout_hw_to_hym8563(hw);
+	struct i2c_client *client = hym8563->client;
+	int ret = i2c_smbus_read_byte_data(client, HYM8563_CLKOUT);
+	int i;
+
+	if (ret < 0)
+		return ret;
+
+	for (i = 0; i < ARRAY_SIZE(clkout_rates); i++)
+		if (clkout_rates[i] == rate) {
+			ret &= ~HYM8563_CLKOUT_MASK;
+			ret |= i;
+			return i2c_smbus_write_byte_data(client,
+							 HYM8563_CLKOUT, ret);
+		}
+
+	return -EINVAL;
+}
+
+static int hym8563_clkout_control(struct clk_hw *hw, bool enable)
+{
+	struct hym8563 *hym8563 = clkout_hw_to_hym8563(hw);
+	struct i2c_client *client = hym8563->client;
+	int ret = i2c_smbus_read_byte_data(client, HYM8563_CLKOUT);
+
+	if (ret < 0)
+		return ret;
+
+	if (enable)
+		ret |= HYM8563_CLKOUT_ENABLE;
+	else
+		ret &= ~HYM8563_CLKOUT_ENABLE;
+
+	return i2c_smbus_write_byte_data(client, HYM8563_CLKOUT, ret);
+}
+
+static int hym8563_clkout_prepare(struct clk_hw *hw)
+{
+	return hym8563_clkout_control(hw, 1);
+}
+
+static void hym8563_clkout_unprepare(struct clk_hw *hw)
+{
+	hym8563_clkout_control(hw, 0);
+}
+
+static int hym8563_clkout_is_prepared(struct clk_hw *hw)
+{
+	struct hym8563 *hym8563 = clkout_hw_to_hym8563(hw);
+	struct i2c_client *client = hym8563->client;
+	int ret = i2c_smbus_read_byte_data(client, HYM8563_CLKOUT);
+
+	if (ret < 0)
+		return ret;
+
+	return !!(ret & HYM8563_CLKOUT_ENABLE);
+}
+
+static const struct clk_ops hym8563_clkout_ops = {
+	.prepare = hym8563_clkout_prepare,
+	.unprepare = hym8563_clkout_unprepare,
+	.is_prepared = hym8563_clkout_is_prepared,
+	.recalc_rate = hym8563_clkout_recalc_rate,
+	.determine_rate = hym8563_clkout_determine_rate,
+	.set_rate = hym8563_clkout_set_rate,
+};
+
+static struct clk *hym8563_clkout_register_clk(struct hym8563 *hym8563)
+{
+	struct i2c_client *client = hym8563->client;
+	struct device_node *node = client->dev.of_node;
+	struct clk *clk;
+	struct clk_init_data init;
+	int ret;
+
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CLKOUT,
+						0);
+	if (ret < 0)
+		return ERR_PTR(ret);
+
+	init.name = "hym8563-clkout";
+	init.ops = &hym8563_clkout_ops;
+	init.flags = 0;
+	init.parent_names = NULL;
+	init.num_parents = 0;
+	hym8563->clkout_hw.init = &init;
+
+	/* optional override of the clockname */
+	of_property_read_string(node, "clock-output-names", &init.name);
+
+	/* register the clock */
+	clk = clk_register(&client->dev, &hym8563->clkout_hw);
+
+	if (!IS_ERR(clk))
+		of_clk_add_provider(node, of_clk_src_simple_get, clk);
+
+	return clk;
+}
+#endif
+
+/*
+ * The alarm interrupt is implemented as a level-low interrupt in the
+ * hym8563, while the timer interrupt uses a falling edge.
+ * We don't use the timer at all, so the interrupt is requested to
+ * use the level-low trigger.
+ */
+static irqreturn_t hym8563_irq(int irq, void *dev_id)
+{
+	struct hym8563 *hym8563 = (struct hym8563 *)dev_id;
+	struct i2c_client *client = hym8563->client;
+	int data, ret;
+
+	rtc_lock(hym8563->rtc);
+
+	/* Clear the alarm flag */
+
+	data = i2c_smbus_read_byte_data(client, HYM8563_CTL2);
+	if (data < 0) {
+		dev_err(&client->dev, "%s: error reading i2c data %d\n",
+			__func__, data);
+		goto out;
+	}
+
+	data &= ~HYM8563_CTL2_AF;
+
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CTL2, data);
+	if (ret < 0) {
+		dev_err(&client->dev, "%s: error writing i2c data %d\n",
+			__func__, ret);
+	}
+
+out:
+	rtc_unlock(hym8563->rtc);
+	return IRQ_HANDLED;
+}
+
+static int hym8563_init_device(struct i2c_client *client)
+{
+	int ret;
+
+	/* Clear stop flag if present */
+	ret = i2c_smbus_write_byte_data(client, HYM8563_CTL1, 0);
+	if (ret < 0)
+		return ret;
+
+	ret = i2c_smbus_read_byte_data(client, HYM8563_CTL2);
+	if (ret < 0)
+		return ret;
+
+	/* Disable alarm and timer interrupts */
+	ret &= ~HYM8563_CTL2_AIE;
+	ret &= ~HYM8563_CTL2_TIE;
+
+	/* Clear any pending alarm and timer flags */
+	if (ret & HYM8563_CTL2_AF)
+		ret &= ~HYM8563_CTL2_AF;
+
+	if (ret & HYM8563_CTL2_TF)
+		ret &= ~HYM8563_CTL2_TF;
+
+	ret &= ~HYM8563_CTL2_TI_TP;
+
+	return i2c_smbus_write_byte_data(client, HYM8563_CTL2, ret);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int hym8563_suspend(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	int ret;
+
+	if (device_may_wakeup(dev)) {
+		ret = enable_irq_wake(client->irq);
+		if (ret) {
+			dev_err(dev, "enable_irq_wake failed, %d\n", ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int hym8563_resume(struct device *dev)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+
+	if (device_may_wakeup(dev))
+		disable_irq_wake(client->irq);
+
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(hym8563_pm_ops, hym8563_suspend, hym8563_resume);
+
+static int hym8563_probe(struct i2c_client *client)
+{
+	struct hym8563 *hym8563;
+	int ret;
+
+	hym8563 = devm_kzalloc(&client->dev, sizeof(*hym8563), GFP_KERNEL);
+	if (!hym8563)
+		return -ENOMEM;
+
+	hym8563->rtc = devm_rtc_allocate_device(&client->dev);
+	if (IS_ERR(hym8563->rtc))
+		return PTR_ERR(hym8563->rtc);
+
+	hym8563->client = client;
+	i2c_set_clientdata(client, hym8563);
+
+	ret = hym8563_init_device(client);
+	if (ret) {
+		dev_err(&client->dev, "could not init device, %d\n", ret);
+		return ret;
+	}
+
+	if (client->irq > 0) {
+		unsigned long irqflags = IRQF_TRIGGER_LOW;
+
+		if (dev_fwnode(&client->dev))
+			irqflags = 0;
+
+		ret = devm_request_threaded_irq(&client->dev, client->irq,
+						NULL, hym8563_irq,
+						irqflags | IRQF_ONESHOT,
+						client->name, hym8563);
+		if (ret < 0) {
+			dev_err(&client->dev, "irq %d request failed, %d\n",
+				client->irq, ret);
+			return ret;
+		}
+	}
+
+	if (client->irq > 0 ||
+	    device_property_read_bool(&client->dev, "wakeup-source")) {
+		device_init_wakeup(&client->dev, true);
+	}
+
+	/* check state of calendar information */
+	ret = i2c_smbus_read_byte_data(client, HYM8563_SEC);
+	if (ret < 0)
+		return ret;
+
+	dev_dbg(&client->dev, "rtc information is %s\n",
+		(ret & HYM8563_SEC_VL) ? "invalid" : "valid");
+
+	hym8563->rtc->ops = &hym8563_rtc_ops;
+	set_bit(RTC_FEATURE_ALARM_RES_MINUTE, hym8563->rtc->features);
+	clear_bit(RTC_FEATURE_UPDATE_INTERRUPT, hym8563->rtc->features);
+
+#ifdef CONFIG_COMMON_CLK
+	hym8563_clkout_register_clk(hym8563);
+#endif
+
+	return devm_rtc_register_device(hym8563->rtc);
+}
+
+static const struct i2c_device_id hym8563_id[] = {
+	{ .name = "hym8563" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, hym8563_id);
+
+static const struct of_device_id hym8563_dt_idtable[] = {
+	{ .compatible = "haoyu,hym8563" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, hym8563_dt_idtable);
+
+static struct i2c_driver hym8563_driver = {
+	.driver		= {
+		.name	= "rtc-hym8563",
+		.pm	= &hym8563_pm_ops,
+		.of_match_table	= hym8563_dt_idtable,
+	},
+	.probe		= hym8563_probe,
+	.id_table	= hym8563_id,
+};
+
+module_i2c_driver(hym8563_driver);
+
+MODULE_AUTHOR("Heiko Stuebner <heiko@sntech.de>");
+MODULE_DESCRIPTION("HYM8563 RTC driver");
+MODULE_LICENSE("GPL");