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, 355 insertions, 0 deletions

diff --git a/drivers/clocksource/timer-fsl-ftm.c b/drivers/clocksource/timer-fsl-ftm.c
new file mode 100644
index 000000000..4eed6cb46
--- /dev/null
+++ b/drivers/clocksource/timer-fsl-ftm.c
@@ -0,0 +1,355 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Freescale FlexTimer Module (FTM) timer driver.
+ *
+ * Copyright 2014 Freescale Semiconductor, Inc.
+ */
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/clocksource.h>
+#include <linux/err.h>
+#include <linux/interrupt.h>
+#include <linux/io.h>
+#include <linux/of_address.h>
+#include <linux/of_irq.h>
+#include <linux/sched_clock.h>
+#include <linux/slab.h>
+#include <linux/fsl/ftm.h>
+
+#define FTM_SC_CLK(c)	((c) << FTM_SC_CLK_MASK_SHIFT)
+
+struct ftm_clock_device {
+	void __iomem *clksrc_base;
+	void __iomem *clkevt_base;
+	unsigned long periodic_cyc;
+	unsigned long ps;
+	bool big_endian;
+};
+
+static struct ftm_clock_device *priv;
+
+static inline u32 ftm_readl(void __iomem *addr)
+{
+	if (priv->big_endian)
+		return ioread32be(addr);
+	else
+		return ioread32(addr);
+}
+
+static inline void ftm_writel(u32 val, void __iomem *addr)
+{
+	if (priv->big_endian)
+		iowrite32be(val, addr);
+	else
+		iowrite32(val, addr);
+}
+
+static inline void ftm_counter_enable(void __iomem *base)
+{
+	u32 val;
+
+	/* select and enable counter clock source */
+	val = ftm_readl(base + FTM_SC);
+	val &= ~(FTM_SC_PS_MASK | FTM_SC_CLK_MASK);
+	val |= priv->ps | FTM_SC_CLK(1);
+	ftm_writel(val, base + FTM_SC);
+}
+
+static inline void ftm_counter_disable(void __iomem *base)
+{
+	u32 val;
+
+	/* disable counter clock source */
+	val = ftm_readl(base + FTM_SC);
+	val &= ~(FTM_SC_PS_MASK | FTM_SC_CLK_MASK);
+	ftm_writel(val, base + FTM_SC);
+}
+
+static inline void ftm_irq_acknowledge(void __iomem *base)
+{
+	u32 val;
+
+	val = ftm_readl(base + FTM_SC);
+	val &= ~FTM_SC_TOF;
+	ftm_writel(val, base + FTM_SC);
+}
+
+static inline void ftm_irq_enable(void __iomem *base)
+{
+	u32 val;
+
+	val = ftm_readl(base + FTM_SC);
+	val |= FTM_SC_TOIE;
+	ftm_writel(val, base + FTM_SC);
+}
+
+static inline void ftm_irq_disable(void __iomem *base)
+{
+	u32 val;
+
+	val = ftm_readl(base + FTM_SC);
+	val &= ~FTM_SC_TOIE;
+	ftm_writel(val, base + FTM_SC);
+}
+
+static inline void ftm_reset_counter(void __iomem *base)
+{
+	/*
+	 * The CNT register contains the FTM counter value.
+	 * Reset clears the CNT register. Writing any value to COUNT
+	 * updates the counter with its initial value, CNTIN.
+	 */
+	ftm_writel(0x00, base + FTM_CNT);
+}
+
+static u64 notrace ftm_read_sched_clock(void)
+{
+	return ftm_readl(priv->clksrc_base + FTM_CNT);
+}
+
+static int ftm_set_next_event(unsigned long delta,
+				struct clock_event_device *unused)
+{
+	/*
+	 * The CNNIN and MOD are all double buffer registers, writing
+	 * to the MOD register latches the value into a buffer. The MOD
+	 * register is updated with the value of its write buffer with
+	 * the following scenario:
+	 * a, the counter source clock is disabled.
+	 */
+	ftm_counter_disable(priv->clkevt_base);
+
+	/* Force the value of CNTIN to be loaded into the FTM counter */
+	ftm_reset_counter(priv->clkevt_base);
+
+	/*
+	 * The counter increments until the value of MOD is reached,
+	 * at which point the counter is reloaded with the value of CNTIN.
+	 * The TOF (the overflow flag) bit is set when the FTM counter
+	 * changes from MOD to CNTIN. So we should using the delta - 1.
+	 */
+	ftm_writel(delta - 1, priv->clkevt_base + FTM_MOD);
+
+	ftm_counter_enable(priv->clkevt_base);
+
+	ftm_irq_enable(priv->clkevt_base);
+
+	return 0;
+}
+
+static int ftm_set_oneshot(struct clock_event_device *evt)
+{
+	ftm_counter_disable(priv->clkevt_base);
+	return 0;
+}
+
+static int ftm_set_periodic(struct clock_event_device *evt)
+{
+	ftm_set_next_event(priv->periodic_cyc, evt);
+	return 0;
+}
+
+static irqreturn_t ftm_evt_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *evt = dev_id;
+
+	ftm_irq_acknowledge(priv->clkevt_base);
+
+	if (likely(clockevent_state_oneshot(evt))) {
+		ftm_irq_disable(priv->clkevt_base);
+		ftm_counter_disable(priv->clkevt_base);
+	}
+
+	evt->event_handler(evt);
+
+	return IRQ_HANDLED;
+}
+
+static struct clock_event_device ftm_clockevent = {
+	.name			= "Freescale ftm timer",
+	.features		= CLOCK_EVT_FEAT_PERIODIC |
+				  CLOCK_EVT_FEAT_ONESHOT,
+	.set_state_periodic	= ftm_set_periodic,
+	.set_state_oneshot	= ftm_set_oneshot,
+	.set_next_event		= ftm_set_next_event,
+	.rating			= 300,
+};
+
+static int __init ftm_clockevent_init(unsigned long freq, int irq)
+{
+	int err;
+
+	ftm_writel(0x00, priv->clkevt_base + FTM_CNTIN);
+	ftm_writel(~0u, priv->clkevt_base + FTM_MOD);
+
+	ftm_reset_counter(priv->clkevt_base);
+
+	err = request_irq(irq, ftm_evt_interrupt, IRQF_TIMER | IRQF_IRQPOLL,
+			  "Freescale ftm timer", &ftm_clockevent);
+	if (err) {
+		pr_err("ftm: setup irq failed: %d\n", err);
+		return err;
+	}
+
+	ftm_clockevent.cpumask = cpumask_of(0);
+	ftm_clockevent.irq = irq;
+
+	clockevents_config_and_register(&ftm_clockevent,
+					freq / (1 << priv->ps),
+					1, 0xffff);
+
+	ftm_counter_enable(priv->clkevt_base);
+
+	return 0;
+}
+
+static int __init ftm_clocksource_init(unsigned long freq)
+{
+	int err;
+
+	ftm_writel(0x00, priv->clksrc_base + FTM_CNTIN);
+	ftm_writel(~0u, priv->clksrc_base + FTM_MOD);
+
+	ftm_reset_counter(priv->clksrc_base);
+
+	sched_clock_register(ftm_read_sched_clock, 16, freq / (1 << priv->ps));
+	err = clocksource_mmio_init(priv->clksrc_base + FTM_CNT, "fsl-ftm",
+				    freq / (1 << priv->ps), 300, 16,
+				    clocksource_mmio_readl_up);
+	if (err) {
+		pr_err("ftm: init clock source mmio failed: %d\n", err);
+		return err;
+	}
+
+	ftm_counter_enable(priv->clksrc_base);
+
+	return 0;
+}
+
+static int __init __ftm_clk_init(struct device_node *np, char *cnt_name,
+				 char *ftm_name)
+{
+	struct clk *clk;
+	int err;
+
+	clk = of_clk_get_by_name(np, cnt_name);
+	if (IS_ERR(clk)) {
+		pr_err("ftm: Cannot get \"%s\": %ld\n", cnt_name, PTR_ERR(clk));
+		return PTR_ERR(clk);
+	}
+	err = clk_prepare_enable(clk);
+	if (err) {
+		pr_err("ftm: clock failed to prepare+enable \"%s\": %d\n",
+			cnt_name, err);
+		return err;
+	}
+
+	clk = of_clk_get_by_name(np, ftm_name);
+	if (IS_ERR(clk)) {
+		pr_err("ftm: Cannot get \"%s\": %ld\n", ftm_name, PTR_ERR(clk));
+		return PTR_ERR(clk);
+	}
+	err = clk_prepare_enable(clk);
+	if (err)
+		pr_err("ftm: clock failed to prepare+enable \"%s\": %d\n",
+			ftm_name, err);
+
+	return clk_get_rate(clk);
+}
+
+static unsigned long __init ftm_clk_init(struct device_node *np)
+{
+	long freq;
+
+	freq = __ftm_clk_init(np, "ftm-evt-counter-en", "ftm-evt");
+	if (freq <= 0)
+		return 0;
+
+	freq = __ftm_clk_init(np, "ftm-src-counter-en", "ftm-src");
+	if (freq <= 0)
+		return 0;
+
+	return freq;
+}
+
+static int __init ftm_calc_closest_round_cyc(unsigned long freq)
+{
+	priv->ps = 0;
+
+	/* The counter register is only using the lower 16 bits, and
+	 * if the 'freq' value is to big here, then the periodic_cyc
+	 * may exceed 0xFFFF.
+	 */
+	do {
+		priv->periodic_cyc = DIV_ROUND_CLOSEST(freq,
+						HZ * (1 << priv->ps++));
+	} while (priv->periodic_cyc > 0xFFFF);
+
+	if (priv->ps > FTM_PS_MAX) {
+		pr_err("ftm: the prescaler is %lu > %d\n",
+				priv->ps, FTM_PS_MAX);
+		return -EINVAL;
+	}
+
+	return 0;
+}
+
+static int __init ftm_timer_init(struct device_node *np)
+{
+	unsigned long freq;
+	int ret, irq;
+
+	priv = kzalloc_obj(*priv);
+	if (!priv)
+		return -ENOMEM;
+
+	ret = -ENXIO;
+	priv->clkevt_base = of_iomap(np, 0);
+	if (!priv->clkevt_base) {
+		pr_err("ftm: unable to map event timer registers\n");
+		goto err_clkevt;
+	}
+
+	priv->clksrc_base = of_iomap(np, 1);
+	if (!priv->clksrc_base) {
+		pr_err("ftm: unable to map source timer registers\n");
+		goto err_clksrc;
+	}
+
+	ret = -EINVAL;
+	irq = irq_of_parse_and_map(np, 0);
+	if (irq <= 0) {
+		pr_err("ftm: unable to get IRQ from DT, %d\n", irq);
+		goto err;
+	}
+
+	priv->big_endian = of_property_read_bool(np, "big-endian");
+
+	freq = ftm_clk_init(np);
+	if (!freq)
+		goto err;
+
+	ret = ftm_calc_closest_round_cyc(freq);
+	if (ret)
+		goto err;
+
+	ret = ftm_clocksource_init(freq);
+	if (ret)
+		goto err;
+
+	ret = ftm_clockevent_init(freq, irq);
+	if (ret)
+		goto err;
+
+	return 0;
+
+err:
+	iounmap(priv->clksrc_base);
+err_clksrc:
+	iounmap(priv->clkevt_base);
+err_clkevt:
+	kfree(priv);
+	return ret;
+}
+TIMER_OF_DECLARE(flextimer, "fsl,ftm-timer", ftm_timer_init);