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, 306 insertions, 0 deletions

diff --git a/drivers/clocksource/mips-gic-timer.c b/drivers/clocksource/mips-gic-timer.c
new file mode 100644
index 000000000..a1669266c
--- /dev/null
+++ b/drivers/clocksource/mips-gic-timer.c
@@ -0,0 +1,306 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (C) 2012 MIPS Technologies, Inc.  All rights reserved.
+
+#define pr_fmt(fmt) "mips-gic-timer: " fmt
+
+#include <linux/clk.h>
+#include <linux/clockchips.h>
+#include <linux/cpu.h>
+#include <linux/init.h>
+#include <linux/interrupt.h>
+#include <linux/notifier.h>
+#include <linux/of_irq.h>
+#include <linux/percpu.h>
+#include <linux/sched_clock.h>
+#include <linux/smp.h>
+#include <linux/time.h>
+#include <asm/mips-cps.h>
+
+static DEFINE_PER_CPU(struct clock_event_device, gic_clockevent_device);
+static int gic_timer_irq;
+static unsigned int gic_frequency;
+static unsigned int gic_count_width;
+static bool __read_mostly gic_clock_unstable;
+
+static void gic_clocksource_unstable(char *reason);
+
+static u64 notrace gic_read_count_2x32(void)
+{
+	unsigned int hi, hi2, lo;
+
+	do {
+		hi = read_gic_counter_32h();
+		lo = read_gic_counter_32l();
+		hi2 = read_gic_counter_32h();
+	} while (hi2 != hi);
+
+	return (((u64) hi) << 32) + lo;
+}
+
+static u64 notrace gic_read_count_64(void)
+{
+	return read_gic_counter();
+}
+
+static u64 notrace gic_read_count(void)
+{
+	if (mips_cm_is64)
+		return gic_read_count_64();
+
+	return gic_read_count_2x32();
+}
+
+static int gic_next_event(unsigned long delta, struct clock_event_device *evt)
+{
+	int cpu = cpumask_first(evt->cpumask);
+	u64 cnt;
+	int res;
+
+	cnt = gic_read_count();
+	cnt += (u64)delta;
+	if (cpu == raw_smp_processor_id()) {
+		write_gic_vl_compare(cnt);
+	} else {
+		write_gic_vl_other(mips_cm_vp_id(cpu));
+		write_gic_vo_compare(cnt);
+	}
+	res = ((int)(gic_read_count() - cnt) >= 0) ? -ETIME : 0;
+	return res;
+}
+
+static irqreturn_t gic_compare_interrupt(int irq, void *dev_id)
+{
+	struct clock_event_device *cd = dev_id;
+
+	write_gic_vl_compare(read_gic_vl_compare());
+	cd->event_handler(cd);
+	return IRQ_HANDLED;
+}
+
+static void gic_clockevent_cpu_init(unsigned int cpu,
+				    struct clock_event_device *cd)
+{
+	cd->name		= "MIPS GIC";
+	cd->features		= CLOCK_EVT_FEAT_ONESHOT |
+				  CLOCK_EVT_FEAT_C3STOP;
+
+	cd->rating		= 350;
+	cd->irq			= gic_timer_irq;
+	cd->cpumask		= cpumask_of(cpu);
+	cd->set_next_event	= gic_next_event;
+
+	clockevents_config_and_register(cd, gic_frequency, 0x300, 0x7fffffff);
+
+	enable_percpu_irq(gic_timer_irq, IRQ_TYPE_NONE);
+}
+
+static void gic_clockevent_cpu_exit(struct clock_event_device *cd)
+{
+	disable_percpu_irq(gic_timer_irq);
+}
+
+static void gic_update_frequency(void *data)
+{
+	unsigned long rate = (unsigned long)data;
+
+	clockevents_update_freq(this_cpu_ptr(&gic_clockevent_device), rate);
+}
+
+static int gic_starting_cpu(unsigned int cpu)
+{
+	/* Ensure the GIC counter is running */
+	clear_gic_config(GIC_CONFIG_COUNTSTOP);
+
+	gic_clockevent_cpu_init(cpu, this_cpu_ptr(&gic_clockevent_device));
+	return 0;
+}
+
+static int gic_clk_notifier(struct notifier_block *nb, unsigned long action,
+			    void *data)
+{
+	struct clk_notifier_data *cnd = data;
+
+	if (action == POST_RATE_CHANGE) {
+		gic_clocksource_unstable("ref clock rate change");
+		on_each_cpu(gic_update_frequency, (void *)cnd->new_rate, 1);
+	}
+
+	return NOTIFY_OK;
+}
+
+static int gic_dying_cpu(unsigned int cpu)
+{
+	gic_clockevent_cpu_exit(this_cpu_ptr(&gic_clockevent_device));
+	return 0;
+}
+
+static struct notifier_block gic_clk_nb = {
+	.notifier_call = gic_clk_notifier,
+};
+
+static int gic_clockevent_init(void)
+{
+	int ret;
+
+	if (!gic_frequency)
+		return -ENXIO;
+
+	ret = request_percpu_irq(gic_timer_irq, gic_compare_interrupt,
+				 "timer", &gic_clockevent_device);
+	if (ret < 0) {
+		pr_err("IRQ %d setup failed (%d)\n", gic_timer_irq, ret);
+		return ret;
+	}
+
+	cpuhp_setup_state(CPUHP_AP_MIPS_GIC_TIMER_STARTING,
+			  "clockevents/mips/gic/timer:starting",
+			  gic_starting_cpu, gic_dying_cpu);
+	return 0;
+}
+
+static u64 gic_hpt_read(struct clocksource *cs)
+{
+	return gic_read_count();
+}
+
+static u64 gic_hpt_read_multicluster(struct clocksource *cs)
+{
+	unsigned int hi, hi2, lo;
+	u64 count;
+
+	mips_cm_lock_other(0, 0, 0, CM_GCR_Cx_OTHER_BLOCK_GLOBAL);
+
+	if (mips_cm_is64) {
+		count = read_gic_redir_counter();
+		goto out;
+	}
+
+	hi = read_gic_redir_counter_32h();
+	while (true) {
+		lo = read_gic_redir_counter_32l();
+
+		/* If hi didn't change then lo didn't wrap & we're done */
+		hi2 = read_gic_redir_counter_32h();
+		if (hi2 == hi)
+			break;
+
+		/* Otherwise, repeat with the latest hi value */
+		hi = hi2;
+	}
+
+	count = (((u64)hi) << 32) + lo;
+out:
+	mips_cm_unlock_other();
+	return count;
+}
+
+static struct clocksource gic_clocksource = {
+	.name			= "GIC",
+	.read			= gic_hpt_read,
+	.flags			= CLOCK_SOURCE_IS_CONTINUOUS,
+#ifdef CONFIG_GENERIC_GETTIMEOFDAY
+	.vdso_clock_mode	= VDSO_CLOCKMODE_GIC,
+#endif
+};
+
+static void gic_clocksource_unstable(char *reason)
+{
+	if (gic_clock_unstable)
+		return;
+
+	gic_clock_unstable = true;
+
+	pr_info("GIC timer is unstable due to %s\n", reason);
+
+	clocksource_mark_unstable(&gic_clocksource);
+}
+
+static int __init __gic_clocksource_init(void)
+{
+	int ret;
+
+	/* Set clocksource mask. */
+	gic_count_width = read_gic_config() & GIC_CONFIG_COUNTBITS;
+	gic_count_width >>= __ffs(GIC_CONFIG_COUNTBITS);
+	gic_count_width *= 4;
+	gic_count_width += 32;
+	gic_clocksource.mask = CLOCKSOURCE_MASK(gic_count_width);
+
+	/* Calculate a somewhat reasonable rating value. */
+	if (mips_cm_revision() >= CM_REV_CM3 || !IS_ENABLED(CONFIG_CPU_FREQ))
+		gic_clocksource.rating = 300; /* Good when frequecy is stable */
+	else
+		gic_clocksource.rating = 200;
+	gic_clocksource.rating += clamp(gic_frequency / 10000000, 0, 99);
+
+	if (mips_cps_multicluster_cpus()) {
+		gic_clocksource.read = &gic_hpt_read_multicluster;
+		gic_clocksource.vdso_clock_mode = VDSO_CLOCKMODE_NONE;
+	}
+
+	ret = clocksource_register_hz(&gic_clocksource, gic_frequency);
+	if (ret < 0)
+		pr_warn("Unable to register clocksource\n");
+
+	return ret;
+}
+
+static int __init gic_clocksource_of_init(struct device_node *node)
+{
+	struct clk *clk;
+	int ret;
+
+	if (!mips_gic_present() || !node->parent ||
+	    !of_device_is_compatible(node->parent, "mti,gic")) {
+		pr_warn("No DT definition\n");
+		return -ENXIO;
+	}
+
+	clk = of_clk_get(node, 0);
+	if (!IS_ERR(clk)) {
+		ret = clk_prepare_enable(clk);
+		if (ret < 0) {
+			pr_err("Failed to enable clock\n");
+			clk_put(clk);
+			return ret;
+		}
+
+		gic_frequency = clk_get_rate(clk);
+	} else if (of_property_read_u32(node, "clock-frequency",
+					&gic_frequency)) {
+		pr_err("Frequency not specified\n");
+		return -EINVAL;
+	}
+	gic_timer_irq = irq_of_parse_and_map(node, 0);
+	if (!gic_timer_irq) {
+		pr_err("IRQ not specified\n");
+		return -EINVAL;
+	}
+
+	ret = __gic_clocksource_init();
+	if (ret)
+		return ret;
+
+	ret = gic_clockevent_init();
+	if (!ret && !IS_ERR(clk)) {
+		if (clk_notifier_register(clk, &gic_clk_nb) < 0)
+			pr_warn("Unable to register clock notifier\n");
+	}
+
+	/*
+	 * It's safe to use the MIPS GIC timer as a sched clock source only if
+	 * its ticks are stable, which is true on either the platforms with
+	 * stable CPU frequency or on the platforms with CM3 and CPU frequency
+	 * change performed by the CPC core clocks divider.
+	 */
+	if ((mips_cm_revision() >= CM_REV_CM3 || !IS_ENABLED(CONFIG_CPU_FREQ)) &&
+	     !mips_cps_multicluster_cpus()) {
+		sched_clock_register(mips_cm_is64 ?
+				     gic_read_count_64 : gic_read_count_2x32,
+				     gic_count_width, gic_frequency);
+	}
+
+	return 0;
+}
+TIMER_OF_DECLARE(mips_gic_timer, "mti,gic-timer",
+		       gic_clocksource_of_init);