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, 176 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-owl.c b/drivers/clocksource/timer-owl.c
new file mode 100644
index 000000000..ac97420bf
--- /dev/null
+++ b/drivers/clocksource/timer-owl.c
@@ -0,0 +1,176 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Actions Semi Owl timer
+ *
+ * Copyright 2012 Actions Semi Inc.
+ * Author: Actions Semi, Inc.
+ *
+ * Copyright (c) 2017 SUSE Linux GmbH
+ * Author: Andreas Färber
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/interrupt.h>
+#include <linux/irq.h>
+#include <linux/irqreturn.h>
+#include <linux/sched_clock.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+
+#define OWL_Tx_CTL		0x0
+#define OWL_Tx_CMP		0x4
+#define OWL_Tx_VAL		0x8
+
+#define OWL_Tx_CTL_PD		BIT(0)
+#define OWL_Tx_CTL_INTEN	BIT(1)
+#define OWL_Tx_CTL_EN		BIT(2)
+
+static void __iomem *owl_timer_base;
+static void __iomem *owl_clksrc_base;
+static void __iomem *owl_clkevt_base;
+
+static inline void owl_timer_reset(void __iomem *base)
+{
+	writel(0, base + OWL_Tx_CTL);
+	writel(0, base + OWL_Tx_VAL);
+	writel(0, base + OWL_Tx_CMP);
+}
+
+static inline void owl_timer_set_enabled(void __iomem *base, bool enabled)
+{
+	u32 ctl = readl(base + OWL_Tx_CTL);
+
+	/* PD bit is cleared when set */
+	ctl &= ~OWL_Tx_CTL_PD;
+
+	if (enabled)
+		ctl |= OWL_Tx_CTL_EN;
+	else
+		ctl &= ~OWL_Tx_CTL_EN;
+
+	writel(ctl, base + OWL_Tx_CTL);
+}
+
+static u64 notrace owl_timer_sched_read(void)
+{
+	return (u64)readl(owl_clksrc_base + OWL_Tx_VAL);
+}
+
+static int owl_timer_set_state_shutdown(struct clock_event_device *evt)
+{
+	owl_timer_set_enabled(owl_clkevt_base, false);
+
+	return 0;
+}
+
+static int owl_timer_set_state_oneshot(struct clock_event_device *evt)
+{
+	owl_timer_reset(owl_clkevt_base);
+
+	return 0;
+}
+
+static int owl_timer_tick_resume(struct clock_event_device *evt)
+{
+	return 0;
+}
+
+static int owl_timer_set_next_event(unsigned long evt,
+				    struct clock_event_device *ev)
+{
+	void __iomem *base = owl_clkevt_base;
+
+	owl_timer_set_enabled(base, false);
+	writel(OWL_Tx_CTL_INTEN, base + OWL_Tx_CTL);
+	writel(0, base + OWL_Tx_VAL);
+	writel(evt, base + OWL_Tx_CMP);
+	owl_timer_set_enabled(base, true);
+
+	return 0;
+}
+
+static struct clock_event_device owl_clockevent = {
+	.name			= "owl_tick",
+	.rating			= 200,
+	.features		= CLOCK_EVT_FEAT_ONESHOT |
+				  CLOCK_EVT_FEAT_DYNIRQ,
+	.set_state_shutdown	= owl_timer_set_state_shutdown,
+	.set_state_oneshot	= owl_timer_set_state_oneshot,
+	.tick_resume		= owl_timer_tick_resume,
+	.set_next_event		= owl_timer_set_next_event,
+};
+
+static irqreturn_t owl_timer1_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = (struct clock_event_device *)dev_id;
+
+	writel(OWL_Tx_CTL_PD, owl_clkevt_base + OWL_Tx_CTL);
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static int __init owl_timer_init(struct device_node *node)
+{
+	struct clk *clk;
+	unsigned long rate;
+	int timer1_irq, ret;
+
+	owl_timer_base = of_io_request_and_map(node, 0, "owl-timer");
+	if (IS_ERR(owl_timer_base)) {
+		pr_err("Can't map timer registers\n");
+		return PTR_ERR(owl_timer_base);
+	}
+
+	owl_clksrc_base = owl_timer_base + 0x08;
+	owl_clkevt_base = owl_timer_base + 0x14;
+
+	timer1_irq = of_irq_get_byname(node, "timer1");
+	if (timer1_irq <= 0) {
+		pr_err("Can't parse timer1 IRQ\n");
+		return -EINVAL;
+	}
+
+	clk = of_clk_get(node, 0);
+	if (IS_ERR(clk)) {
+		ret = PTR_ERR(clk);
+		pr_err("Failed to get clock for clocksource (%d)\n", ret);
+		return ret;
+	}
+
+	rate = clk_get_rate(clk);
+
+	owl_timer_reset(owl_clksrc_base);
+	owl_timer_set_enabled(owl_clksrc_base, true);
+
+	sched_clock_register(owl_timer_sched_read, 32, rate);
+	ret = clocksource_mmio_init(owl_clksrc_base + OWL_Tx_VAL, node->name,
+				    rate, 200, 32, clocksource_mmio_readl_up);
+	if (ret) {
+		pr_err("Failed to register clocksource (%d)\n", ret);
+		return ret;
+	}
+
+	owl_timer_reset(owl_clkevt_base);
+
+	ret = request_irq(timer1_irq, owl_timer1_interrupt, IRQF_TIMER,
+			  "owl-timer", &owl_clockevent);
+	if (ret) {
+		pr_err("failed to request irq %d\n", timer1_irq);
+		return ret;
+	}
+
+	owl_clockevent.cpumask = cpumask_of(0);
+	owl_clockevent.irq = timer1_irq;
+
+	clockevents_config_and_register(&owl_clockevent, rate,
+					0xf, 0xffffffff);
+
+	return 0;
+}
+TIMER_OF_DECLARE(owl_s500, "actions,s500-timer", owl_timer_init);
+TIMER_OF_DECLARE(owl_s700, "actions,s700-timer", owl_timer_init);
+TIMER_OF_DECLARE(owl_s900, "actions,s900-timer", owl_timer_init);