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, 379 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-sun5i.c b/drivers/clocksource/timer-sun5i.c
new file mode 100644
index 000000000..6ab300d22
--- /dev/null
+++ b/drivers/clocksource/timer-sun5i.c
@@ -0,0 +1,379 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Allwinner SoCs hstimer driver.
+ *
+ * Copyright (C) 2013 Maxime Ripard
+ *
+ * Maxime Ripard <maxime.ripard@free-electrons.com>
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqreturn.h>
+#include <linux/reset.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+
+#define TIMER_IRQ_EN_REG			0x00
+#define TIMER_IRQ_EN(val)			BIT(val)
+#define TIMER_IRQ_ST_REG			0x04
+#define TIMER_CTL_REG(val, offset)		(0x20 * (val) + 0x10 + (offset))
+#define TIMER_CTL_ENABLE			BIT(0)
+#define TIMER_CTL_RELOAD			BIT(1)
+#define TIMER_CTL_CLK_PRES(val)			(((val) & 0x7) << 4)
+#define TIMER_CTL_ONESHOT			BIT(7)
+#define TIMER_INTVAL_LO_REG(val, offset)	(0x20 * (val) + 0x14 + (offset))
+#define TIMER_INTVAL_HI_REG(val, offset)	(0x20 * (val) + 0x18 + (offset))
+#define TIMER_CNTVAL_LO_REG(val, offset)	(0x20 * (val) + 0x1c + (offset))
+#define TIMER_CNTVAL_HI_REG(val, offset)	(0x20 * (val) + 0x20 + (offset))
+
+#define TIMER_SYNC_TICKS	3
+
+/**
+ * struct sunxi_timer_quirks - Differences between SoC variants.
+ *
+ * @from_ctl_base_offset: offset applied from ctl register onwards
+ */
+struct sunxi_timer_quirks {
+	u32 from_ctl_base_offset;
+};
+
+struct sun5i_timer {
+	void __iomem		*base;
+	struct clk		*clk;
+	struct notifier_block	clk_rate_cb;
+	u32			ticks_per_jiffy;
+	struct clocksource	clksrc;
+	struct clock_event_device	clkevt;
+	const struct sunxi_timer_quirks *quirks;
+};
+
+#define nb_to_sun5i_timer(x) \
+	container_of(x, struct sun5i_timer, clk_rate_cb)
+#define clksrc_to_sun5i_timer(x) \
+	container_of(x, struct sun5i_timer, clksrc)
+#define clkevt_to_sun5i_timer(x) \
+	container_of(x, struct sun5i_timer, clkevt)
+
+/*
+ * When we disable a timer, we need to wait at least for 2 cycles of
+ * the timer source clock. We will use for that the clocksource timer
+ * that is already setup and runs at the same frequency than the other
+ * timers, and we never will be disabled.
+ */
+static void sun5i_clkevt_sync(struct sun5i_timer *ce)
+{
+	u32 offset = ce->quirks->from_ctl_base_offset;
+	u32 old = readl(ce->base + TIMER_CNTVAL_LO_REG(1, offset));
+
+	while ((old - readl(ce->base + TIMER_CNTVAL_LO_REG(1, offset))) <
+	       TIMER_SYNC_TICKS)
+		cpu_relax();
+}
+
+static void sun5i_clkevt_time_stop(struct sun5i_timer *ce, u8 timer)
+{
+	u32 offset = ce->quirks->from_ctl_base_offset;
+	u32 val = readl(ce->base + TIMER_CTL_REG(timer, offset));
+
+	writel(val & ~TIMER_CTL_ENABLE,
+	       ce->base + TIMER_CTL_REG(timer, offset));
+
+	sun5i_clkevt_sync(ce);
+}
+
+static void sun5i_clkevt_time_setup(struct sun5i_timer *ce, u8 timer, u32 delay)
+{
+	u32 offset = ce->quirks->from_ctl_base_offset;
+
+	writel(delay, ce->base + TIMER_INTVAL_LO_REG(timer, offset));
+}
+
+static void sun5i_clkevt_time_start(struct sun5i_timer *ce, u8 timer, bool periodic)
+{
+	u32 offset = ce->quirks->from_ctl_base_offset;
+	u32 val = readl(ce->base + TIMER_CTL_REG(timer, offset));
+
+	if (periodic)
+		val &= ~TIMER_CTL_ONESHOT;
+	else
+		val |= TIMER_CTL_ONESHOT;
+
+	writel(val | TIMER_CTL_ENABLE | TIMER_CTL_RELOAD,
+	       ce->base + TIMER_CTL_REG(timer, offset));
+}
+
+static int sun5i_clkevt_shutdown(struct clock_event_device *clkevt)
+{
+	struct sun5i_timer *ce = clkevt_to_sun5i_timer(clkevt);
+
+	sun5i_clkevt_time_stop(ce, 0);
+	return 0;
+}
+
+static int sun5i_clkevt_set_oneshot(struct clock_event_device *clkevt)
+{
+	struct sun5i_timer *ce = clkevt_to_sun5i_timer(clkevt);
+
+	sun5i_clkevt_time_stop(ce, 0);
+	sun5i_clkevt_time_start(ce, 0, false);
+	return 0;
+}
+
+static int sun5i_clkevt_set_periodic(struct clock_event_device *clkevt)
+{
+	struct sun5i_timer *ce = clkevt_to_sun5i_timer(clkevt);
+
+	sun5i_clkevt_time_stop(ce, 0);
+	sun5i_clkevt_time_setup(ce, 0, ce->ticks_per_jiffy);
+	sun5i_clkevt_time_start(ce, 0, true);
+	return 0;
+}
+
+static int sun5i_clkevt_next_event(unsigned long evt,
+				   struct clock_event_device *clkevt)
+{
+	struct sun5i_timer *ce = clkevt_to_sun5i_timer(clkevt);
+
+	sun5i_clkevt_time_stop(ce, 0);
+	sun5i_clkevt_time_setup(ce, 0, evt - TIMER_SYNC_TICKS);
+	sun5i_clkevt_time_start(ce, 0, false);
+
+	return 0;
+}
+
+static irqreturn_t sun5i_timer_interrupt(int irq, void *dev_id)
+{
+	struct sun5i_timer *ce = dev_id;
+
+	writel(0x1, ce->base + TIMER_IRQ_ST_REG);
+	ce->clkevt.event_handler(&ce->clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static u64 sun5i_clksrc_read(struct clocksource *clksrc)
+{
+	struct sun5i_timer *cs = clksrc_to_sun5i_timer(clksrc);
+	u32 offset = cs->quirks->from_ctl_base_offset;
+
+	return ~readl(cs->base + TIMER_CNTVAL_LO_REG(1, offset));
+}
+
+static int sun5i_rate_cb(struct notifier_block *nb,
+			 unsigned long event, void *data)
+{
+	struct clk_notifier_data *ndata = data;
+	struct sun5i_timer *cs = nb_to_sun5i_timer(nb);
+
+	switch (event) {
+	case PRE_RATE_CHANGE:
+		clocksource_unregister(&cs->clksrc);
+		break;
+
+	case POST_RATE_CHANGE:
+		clocksource_register_hz(&cs->clksrc, ndata->new_rate);
+		clockevents_update_freq(&cs->clkevt, ndata->new_rate);
+		cs->ticks_per_jiffy = DIV_ROUND_UP(ndata->new_rate, HZ);
+		break;
+
+	default:
+		break;
+	}
+
+	return NOTIFY_DONE;
+}
+
+static int sun5i_setup_clocksource(struct platform_device *pdev,
+				   unsigned long rate)
+{
+	struct sun5i_timer *cs = platform_get_drvdata(pdev);
+	u32 offset = cs->quirks->from_ctl_base_offset;
+	void __iomem *base = cs->base;
+	int ret;
+
+	writel(~0, base + TIMER_INTVAL_LO_REG(1, offset));
+	writel(TIMER_CTL_ENABLE | TIMER_CTL_RELOAD,
+	       base + TIMER_CTL_REG(1, offset));
+
+	cs->clksrc.name = pdev->dev.of_node->name;
+	cs->clksrc.rating = 340;
+	cs->clksrc.read = sun5i_clksrc_read;
+	cs->clksrc.mask = CLOCKSOURCE_MASK(32);
+	cs->clksrc.flags = CLOCK_SOURCE_IS_CONTINUOUS;
+	cs->clksrc.owner = THIS_MODULE;
+
+	ret = clocksource_register_hz(&cs->clksrc, rate);
+	if (ret) {
+		dev_err(&pdev->dev, "Couldn't register clock source.\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static int sun5i_setup_clockevent(struct platform_device *pdev,
+				  unsigned long rate, int irq)
+{
+	struct device *dev = &pdev->dev;
+	struct sun5i_timer *ce = platform_get_drvdata(pdev);
+	void __iomem *base = ce->base;
+	int ret;
+	u32 val;
+
+	ce->clkevt.name = dev->of_node->name;
+	ce->clkevt.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+	ce->clkevt.set_next_event = sun5i_clkevt_next_event;
+	ce->clkevt.set_state_shutdown = sun5i_clkevt_shutdown;
+	ce->clkevt.set_state_periodic = sun5i_clkevt_set_periodic;
+	ce->clkevt.set_state_oneshot = sun5i_clkevt_set_oneshot;
+	ce->clkevt.tick_resume = sun5i_clkevt_shutdown;
+	ce->clkevt.rating = 340;
+	ce->clkevt.irq = irq;
+	ce->clkevt.cpumask = cpu_possible_mask;
+	ce->clkevt.owner = THIS_MODULE;
+
+	/* Enable timer0 interrupt */
+	val = readl(base + TIMER_IRQ_EN_REG);
+	writel(val | TIMER_IRQ_EN(0), base + TIMER_IRQ_EN_REG);
+
+	clockevents_config_and_register(&ce->clkevt, rate,
+					TIMER_SYNC_TICKS, 0xffffffff);
+
+	ret = devm_request_irq(dev, irq, sun5i_timer_interrupt,
+			       IRQF_TIMER | IRQF_IRQPOLL,
+			       "sun5i_timer0", ce);
+	if (ret) {
+		dev_err(dev, "Unable to register interrupt\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static int sun5i_timer_probe(struct platform_device *pdev)
+{
+	const struct sunxi_timer_quirks *quirks;
+	struct device *dev = &pdev->dev;
+	struct sun5i_timer *st;
+	struct reset_control *rstc;
+	void __iomem *timer_base;
+	struct clk *clk;
+	unsigned long rate;
+	int irq, ret;
+
+	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, st);
+
+	timer_base = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(timer_base)) {
+		dev_err(dev, "Can't map registers\n");
+		return PTR_ERR(timer_base);
+	}
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	clk = devm_clk_get_enabled(dev, NULL);
+	if (IS_ERR(clk)) {
+		dev_err(dev, "Can't get timer clock\n");
+		return PTR_ERR(clk);
+	}
+
+	rate = clk_get_rate(clk);
+	if (!rate) {
+		dev_err(dev, "Couldn't get parent clock rate\n");
+		return -EINVAL;
+	}
+
+	quirks = of_device_get_match_data(&pdev->dev);
+	if (!quirks) {
+		dev_err(&pdev->dev, "Failed to determine the quirks to use\n");
+		return -ENODEV;
+	}
+
+	st->base = timer_base;
+	st->ticks_per_jiffy = DIV_ROUND_UP(rate, HZ);
+	st->clk = clk;
+	st->clk_rate_cb.notifier_call = sun5i_rate_cb;
+	st->clk_rate_cb.next = NULL;
+	st->quirks = quirks;
+
+	ret = devm_clk_notifier_register(dev, clk, &st->clk_rate_cb);
+	if (ret) {
+		dev_err(dev, "Unable to register clock notifier.\n");
+		return ret;
+	}
+
+	rstc = devm_reset_control_get_optional_exclusive(dev, NULL);
+	if (IS_ERR(rstc))
+		return dev_err_probe(dev, PTR_ERR(rstc),
+				     "failed to get reset\n");
+	if (rstc)
+		reset_control_deassert(rstc);
+
+	ret = sun5i_setup_clocksource(pdev, rate);
+	if (ret)
+		return ret;
+
+	ret = sun5i_setup_clockevent(pdev, rate, irq);
+	if (ret)
+		goto err_unreg_clocksource;
+
+	return 0;
+
+err_unreg_clocksource:
+	clocksource_unregister(&st->clksrc);
+	return ret;
+}
+
+static void sun5i_timer_remove(struct platform_device *pdev)
+{
+	struct sun5i_timer *st = platform_get_drvdata(pdev);
+
+	clocksource_unregister(&st->clksrc);
+}
+
+static const struct sunxi_timer_quirks sun5i_sun7i_hstimer_quirks = {
+	.from_ctl_base_offset = 0x0,
+};
+
+static const struct sunxi_timer_quirks sun20i_d1_hstimer_quirks = {
+	.from_ctl_base_offset = 0x10,
+};
+
+static const struct of_device_id sun5i_timer_of_match[] = {
+	{
+		.compatible = "allwinner,sun5i-a13-hstimer",
+		.data = &sun5i_sun7i_hstimer_quirks,
+	},
+	{
+		.compatible = "allwinner,sun7i-a20-hstimer",
+		.data = &sun5i_sun7i_hstimer_quirks,
+	},
+	{
+		.compatible = "allwinner,sun20i-d1-hstimer",
+		.data = &sun20i_d1_hstimer_quirks,
+	},
+	{},
+};
+MODULE_DEVICE_TABLE(of, sun5i_timer_of_match);
+
+static struct platform_driver sun5i_timer_driver = {
+	.probe		= sun5i_timer_probe,
+	.remove		= sun5i_timer_remove,
+	.driver	= {
+		.name	= "sun5i-timer",
+		.of_match_table = sun5i_timer_of_match,
+		.suppress_bind_attrs = true,
+	},
+};
+module_platform_driver(sun5i_timer_driver);