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, 304 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-rockchip.c b/drivers/clocksource/timer-rockchip.c
new file mode 100644
index 000000000..540a16667
--- /dev/null
+++ b/drivers/clocksource/timer-rockchip.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Rockchip timer support
+ *
+ * Copyright (C) Daniel Lezcano <daniel.lezcano@linaro.org>
+ */
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/sched_clock.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#define TIMER_NAME "rk_timer"
+
+#define TIMER_LOAD_COUNT0	0x00
+#define TIMER_LOAD_COUNT1	0x04
+#define TIMER_CURRENT_VALUE0	0x08
+#define TIMER_CURRENT_VALUE1	0x0C
+#define TIMER_CONTROL_REG3288	0x10
+#define TIMER_CONTROL_REG3399	0x1c
+#define TIMER_INT_STATUS	0x18
+
+#define TIMER_DISABLE		0x0
+#define TIMER_ENABLE		0x1
+#define TIMER_MODE_FREE_RUNNING			(0 << 1)
+#define TIMER_MODE_USER_DEFINED_COUNT		(1 << 1)
+#define TIMER_INT_UNMASK			(1 << 2)
+
+struct rk_timer {
+	void __iomem *base;
+	void __iomem *ctrl;
+	struct clk *clk;
+	struct clk *pclk;
+	u32 freq;
+	int irq;
+};
+
+struct rk_clkevt {
+	struct clock_event_device ce;
+	struct rk_timer timer;
+};
+
+static struct rk_clkevt *rk_clkevt;
+static struct rk_timer *rk_clksrc;
+
+static inline struct rk_timer *rk_timer(struct clock_event_device *ce)
+{
+	return &container_of(ce, struct rk_clkevt, ce)->timer;
+}
+
+static inline void rk_timer_disable(struct rk_timer *timer)
+{
+	writel_relaxed(TIMER_DISABLE, timer->ctrl);
+}
+
+static inline void rk_timer_enable(struct rk_timer *timer, u32 flags)
+{
+	writel_relaxed(TIMER_ENABLE | flags, timer->ctrl);
+}
+
+static void rk_timer_update_counter(unsigned long cycles,
+				    struct rk_timer *timer)
+{
+	writel_relaxed(cycles, timer->base + TIMER_LOAD_COUNT0);
+	writel_relaxed(0, timer->base + TIMER_LOAD_COUNT1);
+}
+
+static void rk_timer_interrupt_clear(struct rk_timer *timer)
+{
+	writel_relaxed(1, timer->base + TIMER_INT_STATUS);
+}
+
+static inline int rk_timer_set_next_event(unsigned long cycles,
+					  struct clock_event_device *ce)
+{
+	struct rk_timer *timer = rk_timer(ce);
+
+	rk_timer_disable(timer);
+	rk_timer_update_counter(cycles, timer);
+	rk_timer_enable(timer, TIMER_MODE_USER_DEFINED_COUNT |
+			       TIMER_INT_UNMASK);
+	return 0;
+}
+
+static int rk_timer_shutdown(struct clock_event_device *ce)
+{
+	struct rk_timer *timer = rk_timer(ce);
+
+	rk_timer_disable(timer);
+	return 0;
+}
+
+static int rk_timer_set_periodic(struct clock_event_device *ce)
+{
+	struct rk_timer *timer = rk_timer(ce);
+
+	rk_timer_disable(timer);
+	rk_timer_update_counter(timer->freq / HZ - 1, timer);
+	rk_timer_enable(timer, TIMER_MODE_FREE_RUNNING | TIMER_INT_UNMASK);
+	return 0;
+}
+
+static irqreturn_t rk_timer_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *ce = dev_id;
+	struct rk_timer *timer = rk_timer(ce);
+
+	rk_timer_interrupt_clear(timer);
+
+	if (clockevent_state_oneshot(ce))
+		rk_timer_disable(timer);
+
+	ce->event_handler(ce);
+
+	return IRQ_HANDLED;
+}
+
+static u64 notrace rk_timer_sched_read(void)
+{
+	return ~readl_relaxed(rk_clksrc->base + TIMER_CURRENT_VALUE0);
+}
+
+static int __init
+rk_timer_probe(struct rk_timer *timer, struct device_node *np)
+{
+	struct clk *timer_clk;
+	struct clk *pclk;
+	int ret = -EINVAL, irq;
+	u32 ctrl_reg = TIMER_CONTROL_REG3288;
+
+	timer->base = of_iomap(np, 0);
+	if (!timer->base) {
+		pr_err("Failed to get base address for '%s'\n", TIMER_NAME);
+		return -ENXIO;
+	}
+
+	if (of_device_is_compatible(np, "rockchip,rk3399-timer"))
+		ctrl_reg = TIMER_CONTROL_REG3399;
+
+	timer->ctrl = timer->base + ctrl_reg;
+
+	pclk = of_clk_get_by_name(np, "pclk");
+	if (IS_ERR(pclk)) {
+		ret = PTR_ERR(pclk);
+		pr_err("Failed to get pclk for '%s'\n", TIMER_NAME);
+		goto out_unmap;
+	}
+
+	ret = clk_prepare_enable(pclk);
+	if (ret) {
+		pr_err("Failed to enable pclk for '%s'\n", TIMER_NAME);
+		goto out_unmap;
+	}
+	timer->pclk = pclk;
+
+	timer_clk = of_clk_get_by_name(np, "timer");
+	if (IS_ERR(timer_clk)) {
+		ret = PTR_ERR(timer_clk);
+		pr_err("Failed to get timer clock for '%s'\n", TIMER_NAME);
+		goto out_timer_clk;
+	}
+
+	ret = clk_prepare_enable(timer_clk);
+	if (ret) {
+		pr_err("Failed to enable timer clock\n");
+		goto out_timer_clk;
+	}
+	timer->clk = timer_clk;
+
+	timer->freq = clk_get_rate(timer_clk);
+
+	irq = irq_of_parse_and_map(np, 0);
+	if (!irq) {
+		ret = -EINVAL;
+		pr_err("Failed to map interrupts for '%s'\n", TIMER_NAME);
+		goto out_irq;
+	}
+	timer->irq = irq;
+
+	rk_timer_interrupt_clear(timer);
+	rk_timer_disable(timer);
+	return 0;
+
+out_irq:
+	clk_disable_unprepare(timer_clk);
+out_timer_clk:
+	clk_disable_unprepare(pclk);
+out_unmap:
+	iounmap(timer->base);
+
+	return ret;
+}
+
+static void __init rk_timer_cleanup(struct rk_timer *timer)
+{
+	clk_disable_unprepare(timer->clk);
+	clk_disable_unprepare(timer->pclk);
+	iounmap(timer->base);
+}
+
+static int __init rk_clkevt_init(struct device_node *np)
+{
+	struct clock_event_device *ce;
+	int ret = -EINVAL;
+
+	rk_clkevt = kzalloc_obj(struct rk_clkevt);
+	if (!rk_clkevt) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = rk_timer_probe(&rk_clkevt->timer, np);
+	if (ret)
+		goto out_probe;
+
+	ce = &rk_clkevt->ce;
+	ce->name = TIMER_NAME;
+	ce->features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT |
+		       CLOCK_EVT_FEAT_DYNIRQ;
+	ce->set_next_event = rk_timer_set_next_event;
+	ce->set_state_shutdown = rk_timer_shutdown;
+	ce->set_state_periodic = rk_timer_set_periodic;
+	ce->irq = rk_clkevt->timer.irq;
+	ce->cpumask = cpu_possible_mask;
+	ce->rating = 250;
+
+	ret = request_irq(rk_clkevt->timer.irq, rk_timer_interrupt, IRQF_TIMER,
+			  TIMER_NAME, ce);
+	if (ret) {
+		pr_err("Failed to initialize '%s': %d\n",
+			TIMER_NAME, ret);
+		goto out_irq;
+	}
+
+	clockevents_config_and_register(&rk_clkevt->ce,
+					rk_clkevt->timer.freq, 1, UINT_MAX);
+	return 0;
+
+out_irq:
+	rk_timer_cleanup(&rk_clkevt->timer);
+out_probe:
+	kfree(rk_clkevt);
+out:
+	/* Leave rk_clkevt not NULL to prevent future init */
+	rk_clkevt = ERR_PTR(ret);
+	return ret;
+}
+
+static int __init rk_clksrc_init(struct device_node *np)
+{
+	int ret = -EINVAL;
+
+	rk_clksrc = kzalloc_obj(struct rk_timer);
+	if (!rk_clksrc) {
+		ret = -ENOMEM;
+		goto out;
+	}
+
+	ret = rk_timer_probe(rk_clksrc, np);
+	if (ret)
+		goto out_probe;
+
+	rk_timer_update_counter(UINT_MAX, rk_clksrc);
+	rk_timer_enable(rk_clksrc, 0);
+
+	ret = clocksource_mmio_init(rk_clksrc->base + TIMER_CURRENT_VALUE0,
+		TIMER_NAME, rk_clksrc->freq, 250, 32,
+		clocksource_mmio_readl_down);
+	if (ret) {
+		pr_err("Failed to register clocksource\n");
+		goto out_clocksource;
+	}
+
+	sched_clock_register(rk_timer_sched_read, 32, rk_clksrc->freq);
+	return 0;
+
+out_clocksource:
+	rk_timer_cleanup(rk_clksrc);
+out_probe:
+	kfree(rk_clksrc);
+out:
+	/* Leave rk_clksrc not NULL to prevent future init */
+	rk_clksrc = ERR_PTR(ret);
+	return ret;
+}
+
+static int __init rk_timer_init(struct device_node *np)
+{
+	if (!rk_clkevt)
+		return rk_clkevt_init(np);
+
+	if (!rk_clksrc)
+		return rk_clksrc_init(np);
+
+	pr_err("Too many timer definitions for '%s'\n", TIMER_NAME);
+	return -EINVAL;
+}
+
+TIMER_OF_DECLARE(rk3288_timer, "rockchip,rk3288-timer", rk_timer_init);
+TIMER_OF_DECLARE(rk3399_timer, "rockchip,rk3399-timer", rk_timer_init);