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, 341 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-mediatek.c b/drivers/clocksource/timer-mediatek.c
new file mode 100644
index 000000000..7bcb4a3f2
--- /dev/null
+++ b/drivers/clocksource/timer-mediatek.c
@@ -0,0 +1,341 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Mediatek SoCs General-Purpose Timer handling.
+ *
+ * Copyright (C) 2014 Matthias Brugger
+ *
+ * Matthias Brugger <matthias.bgg@gmail.com>
+ */
+
+#define pr_fmt(fmt)	KBUILD_MODNAME ": " fmt
+
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/interrupt.h>
+#include <linux/irqreturn.h>
+#include <linux/sched_clock.h>
+#include <linux/slab.h>
+#include "timer-of.h"
+
+#define TIMER_CLK_EVT           (1)
+#define TIMER_CLK_SRC           (2)
+
+#define TIMER_SYNC_TICKS        (3)
+
+/* gpt */
+#define GPT_IRQ_EN_REG          0x00
+#define GPT_IRQ_ENABLE(val)     BIT((val) - 1)
+#define GPT_IRQ_ACK_REG	        0x08
+#define GPT_IRQ_ACK(val)        BIT((val) - 1)
+
+#define GPT_CTRL_REG(val)       (0x10 * (val))
+#define GPT_CTRL_OP(val)        (((val) & 0x3) << 4)
+#define GPT_CTRL_OP_ONESHOT     (0)
+#define GPT_CTRL_OP_REPEAT      (1)
+#define GPT_CTRL_OP_FREERUN     (3)
+#define GPT_CTRL_CLEAR          (2)
+#define GPT_CTRL_ENABLE         (1)
+#define GPT_CTRL_DISABLE        (0)
+
+#define GPT_CLK_REG(val)        (0x04 + (0x10 * (val)))
+#define GPT_CLK_SRC(val)        (((val) & 0x1) << 4)
+#define GPT_CLK_SRC_SYS13M      (0)
+#define GPT_CLK_SRC_RTC32K      (1)
+#define GPT_CLK_DIV1            (0x0)
+#define GPT_CLK_DIV2            (0x1)
+
+#define GPT_CNT_REG(val)        (0x08 + (0x10 * (val)))
+#define GPT_CMP_REG(val)        (0x0C + (0x10 * (val)))
+
+/* system timer */
+#define SYST_BASE               (0x40)
+
+#define SYST_CON                (SYST_BASE + 0x0)
+#define SYST_VAL                (SYST_BASE + 0x4)
+
+#define SYST_CON_REG(to)        (timer_of_base(to) + SYST_CON)
+#define SYST_VAL_REG(to)        (timer_of_base(to) + SYST_VAL)
+
+/*
+ * SYST_CON_EN: Clock enable. Shall be set to
+ *   - Start timer countdown.
+ *   - Allow timeout ticks being updated.
+ *   - Allow changing interrupt status,like clear irq pending.
+ *
+ * SYST_CON_IRQ_EN: Set to enable interrupt.
+ *
+ * SYST_CON_IRQ_CLR: Set to clear interrupt.
+ */
+#define SYST_CON_EN              BIT(0)
+#define SYST_CON_IRQ_EN          BIT(1)
+#define SYST_CON_IRQ_CLR         BIT(4)
+
+static void __iomem *gpt_sched_reg __read_mostly;
+
+static void mtk_syst_ack_irq(struct timer_of *to)
+{
+	/* Clear and disable interrupt */
+	writel(SYST_CON_EN, SYST_CON_REG(to));
+	writel(SYST_CON_IRQ_CLR | SYST_CON_EN, SYST_CON_REG(to));
+}
+
+static irqreturn_t mtk_syst_handler(int irq, void *dev_id)
+{
+	struct clock_event_device *clkevt = dev_id;
+	struct timer_of *to = to_timer_of(clkevt);
+
+	mtk_syst_ack_irq(to);
+	clkevt->event_handler(clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static int mtk_syst_clkevt_next_event(unsigned long ticks,
+				      struct clock_event_device *clkevt)
+{
+	struct timer_of *to = to_timer_of(clkevt);
+
+	/* Enable clock to allow timeout tick update later */
+	writel(SYST_CON_EN, SYST_CON_REG(to));
+
+	/*
+	 * Write new timeout ticks. Timer shall start countdown
+	 * after timeout ticks are updated.
+	 */
+	writel(ticks, SYST_VAL_REG(to));
+
+	/* Enable interrupt */
+	writel(SYST_CON_EN | SYST_CON_IRQ_EN, SYST_CON_REG(to));
+
+	return 0;
+}
+
+static int mtk_syst_clkevt_shutdown(struct clock_event_device *clkevt)
+{
+	/* Clear any irq */
+	mtk_syst_ack_irq(to_timer_of(clkevt));
+
+	/* Disable timer */
+	writel(0, SYST_CON_REG(to_timer_of(clkevt)));
+
+	return 0;
+}
+
+static int mtk_syst_clkevt_resume(struct clock_event_device *clkevt)
+{
+	return mtk_syst_clkevt_shutdown(clkevt);
+}
+
+static int mtk_syst_clkevt_oneshot(struct clock_event_device *clkevt)
+{
+	return 0;
+}
+
+static u64 notrace mtk_gpt_read_sched_clock(void)
+{
+	return readl_relaxed(gpt_sched_reg);
+}
+
+static void mtk_gpt_clkevt_time_stop(struct timer_of *to, u8 timer)
+{
+	u32 val;
+
+	val = readl(timer_of_base(to) + GPT_CTRL_REG(timer));
+	writel(val & ~GPT_CTRL_ENABLE, timer_of_base(to) +
+	       GPT_CTRL_REG(timer));
+}
+
+static void mtk_gpt_clkevt_time_setup(struct timer_of *to,
+				      unsigned long delay, u8 timer)
+{
+	writel(delay, timer_of_base(to) + GPT_CMP_REG(timer));
+}
+
+static void mtk_gpt_clkevt_time_start(struct timer_of *to,
+				      bool periodic, u8 timer)
+{
+	u32 val;
+
+	/* Acknowledge interrupt */
+	writel(GPT_IRQ_ACK(timer), timer_of_base(to) + GPT_IRQ_ACK_REG);
+
+	val = readl(timer_of_base(to) + GPT_CTRL_REG(timer));
+
+	/* Clear 2 bit timer operation mode field */
+	val &= ~GPT_CTRL_OP(0x3);
+
+	if (periodic)
+		val |= GPT_CTRL_OP(GPT_CTRL_OP_REPEAT);
+	else
+		val |= GPT_CTRL_OP(GPT_CTRL_OP_ONESHOT);
+
+	writel(val | GPT_CTRL_ENABLE | GPT_CTRL_CLEAR,
+	       timer_of_base(to) + GPT_CTRL_REG(timer));
+}
+
+static int mtk_gpt_clkevt_shutdown(struct clock_event_device *clk)
+{
+	mtk_gpt_clkevt_time_stop(to_timer_of(clk), TIMER_CLK_EVT);
+
+	return 0;
+}
+
+static int mtk_gpt_clkevt_set_periodic(struct clock_event_device *clk)
+{
+	struct timer_of *to = to_timer_of(clk);
+
+	mtk_gpt_clkevt_time_stop(to, TIMER_CLK_EVT);
+	mtk_gpt_clkevt_time_setup(to, to->of_clk.period, TIMER_CLK_EVT);
+	mtk_gpt_clkevt_time_start(to, true, TIMER_CLK_EVT);
+
+	return 0;
+}
+
+static int mtk_gpt_clkevt_next_event(unsigned long event,
+				     struct clock_event_device *clk)
+{
+	struct timer_of *to = to_timer_of(clk);
+
+	mtk_gpt_clkevt_time_stop(to, TIMER_CLK_EVT);
+	mtk_gpt_clkevt_time_setup(to, event, TIMER_CLK_EVT);
+	mtk_gpt_clkevt_time_start(to, false, TIMER_CLK_EVT);
+
+	return 0;
+}
+
+static irqreturn_t mtk_gpt_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *clkevt = (struct clock_event_device *)dev_id;
+	struct timer_of *to = to_timer_of(clkevt);
+
+	/* Acknowledge timer0 irq */
+	writel(GPT_IRQ_ACK(TIMER_CLK_EVT), timer_of_base(to) + GPT_IRQ_ACK_REG);
+	clkevt->event_handler(clkevt);
+
+	return IRQ_HANDLED;
+}
+
+static void
+__init mtk_gpt_setup(struct timer_of *to, u8 timer, u8 option)
+{
+	writel(GPT_CTRL_CLEAR | GPT_CTRL_DISABLE,
+	       timer_of_base(to) + GPT_CTRL_REG(timer));
+
+	writel(GPT_CLK_SRC(GPT_CLK_SRC_SYS13M) | GPT_CLK_DIV1,
+	       timer_of_base(to) + GPT_CLK_REG(timer));
+
+	writel(0x0, timer_of_base(to) + GPT_CMP_REG(timer));
+
+	writel(GPT_CTRL_OP(option) | GPT_CTRL_ENABLE,
+	       timer_of_base(to) + GPT_CTRL_REG(timer));
+}
+
+static void mtk_gpt_enable_irq(struct timer_of *to, u8 timer)
+{
+	u32 val;
+
+	/* Disable all interrupts */
+	writel(0x0, timer_of_base(to) + GPT_IRQ_EN_REG);
+
+	/* Acknowledge all spurious pending interrupts */
+	writel(0x3f, timer_of_base(to) + GPT_IRQ_ACK_REG);
+
+	val = readl(timer_of_base(to) + GPT_IRQ_EN_REG);
+	writel(val | GPT_IRQ_ENABLE(timer),
+	       timer_of_base(to) + GPT_IRQ_EN_REG);
+}
+
+static void mtk_gpt_resume(struct clock_event_device *clk)
+{
+	struct timer_of *to = to_timer_of(clk);
+
+	mtk_gpt_enable_irq(to, TIMER_CLK_EVT);
+}
+
+static void mtk_gpt_suspend(struct clock_event_device *clk)
+{
+	struct timer_of *to = to_timer_of(clk);
+
+	/* Disable all interrupts */
+	writel(0x0, timer_of_base(to) + GPT_IRQ_EN_REG);
+
+	/*
+	 * This is called with interrupts disabled,
+	 * so we need to ack any interrupt that is pending
+	 * or for example ATF will prevent a suspend from completing.
+	 */
+	writel(0x3f, timer_of_base(to) + GPT_IRQ_ACK_REG);
+}
+
+static struct timer_of to = {
+	.flags = TIMER_OF_IRQ | TIMER_OF_BASE | TIMER_OF_CLOCK,
+
+	.clkevt = {
+		.name = "mtk-clkevt",
+		.rating = 300,
+		.cpumask = cpu_possible_mask,
+	},
+
+	.of_irq = {
+		.flags = IRQF_TIMER | IRQF_IRQPOLL,
+	},
+};
+
+static int __init mtk_syst_init(struct device_node *node)
+{
+	int ret;
+
+	to.clkevt.features = CLOCK_EVT_FEAT_DYNIRQ | CLOCK_EVT_FEAT_ONESHOT;
+	to.clkevt.set_state_shutdown = mtk_syst_clkevt_shutdown;
+	to.clkevt.set_state_oneshot = mtk_syst_clkevt_oneshot;
+	to.clkevt.tick_resume = mtk_syst_clkevt_resume;
+	to.clkevt.set_next_event = mtk_syst_clkevt_next_event;
+	to.of_irq.handler = mtk_syst_handler;
+
+	ret = timer_of_init(node, &to);
+	if (ret)
+		return ret;
+
+	clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
+					TIMER_SYNC_TICKS, 0xffffffff);
+
+	return 0;
+}
+
+static int __init mtk_gpt_init(struct device_node *node)
+{
+	int ret;
+
+	to.clkevt.features = CLOCK_EVT_FEAT_PERIODIC | CLOCK_EVT_FEAT_ONESHOT;
+	to.clkevt.set_state_shutdown = mtk_gpt_clkevt_shutdown;
+	to.clkevt.set_state_periodic = mtk_gpt_clkevt_set_periodic;
+	to.clkevt.set_state_oneshot = mtk_gpt_clkevt_shutdown;
+	to.clkevt.tick_resume = mtk_gpt_clkevt_shutdown;
+	to.clkevt.set_next_event = mtk_gpt_clkevt_next_event;
+	to.clkevt.suspend = mtk_gpt_suspend;
+	to.clkevt.resume = mtk_gpt_resume;
+	to.of_irq.handler = mtk_gpt_interrupt;
+
+	ret = timer_of_init(node, &to);
+	if (ret)
+		return ret;
+
+	/* Configure clock source */
+	mtk_gpt_setup(&to, TIMER_CLK_SRC, GPT_CTRL_OP_FREERUN);
+	clocksource_mmio_init(timer_of_base(&to) + GPT_CNT_REG(TIMER_CLK_SRC),
+			      node->name, timer_of_rate(&to), 300, 32,
+			      clocksource_mmio_readl_up);
+	gpt_sched_reg = timer_of_base(&to) + GPT_CNT_REG(TIMER_CLK_SRC);
+	sched_clock_register(mtk_gpt_read_sched_clock, 32, timer_of_rate(&to));
+
+	/* Configure clock event */
+	mtk_gpt_setup(&to, TIMER_CLK_EVT, GPT_CTRL_OP_REPEAT);
+	clockevents_config_and_register(&to.clkevt, timer_of_rate(&to),
+					TIMER_SYNC_TICKS, 0xffffffff);
+
+	mtk_gpt_enable_irq(&to, TIMER_CLK_EVT);
+
+	return 0;
+}
+TIMER_OF_DECLARE(mtk_mt6577, "mediatek,mt6577-timer", mtk_gpt_init);
+TIMER_OF_DECLARE(mtk_mt6765, "mediatek,mt6765-timer", mtk_syst_init);