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, 319 insertions, 0 deletions

diff --git a/drivers/powercap/dtpm_cpu.c b/drivers/powercap/dtpm_cpu.c
new file mode 100644
index 000000000..21355db64
--- /dev/null
+++ b/drivers/powercap/dtpm_cpu.c
@@ -0,0 +1,319 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright 2020 Linaro Limited
+ *
+ * Author: Daniel Lezcano <daniel.lezcano@linaro.org>
+ *
+ * The DTPM CPU is based on the energy model. It hooks the CPU in the
+ * DTPM tree which in turns update the power number by propagating the
+ * power number from the CPU energy model information to the parents.
+ *
+ * The association between the power and the performance state, allows
+ * to set the power of the CPU at the OPP granularity.
+ *
+ * The CPU hotplug is supported and the power numbers will be updated
+ * if a CPU is hot plugged / unplugged.
+ */
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/cpumask.h>
+#include <linux/cpufreq.h>
+#include <linux/cpuhotplug.h>
+#include <linux/dtpm.h>
+#include <linux/energy_model.h>
+#include <linux/of.h>
+#include <linux/pm_qos.h>
+#include <linux/slab.h>
+
+struct dtpm_cpu {
+	struct dtpm dtpm;
+	struct freq_qos_request qos_req;
+	int cpu;
+};
+
+static DEFINE_PER_CPU(struct dtpm_cpu *, dtpm_per_cpu);
+
+static struct dtpm_cpu *to_dtpm_cpu(struct dtpm *dtpm)
+{
+	return container_of(dtpm, struct dtpm_cpu, dtpm);
+}
+
+static u64 set_pd_power_limit(struct dtpm *dtpm, u64 power_limit)
+{
+	struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
+	struct em_perf_domain *pd = em_cpu_get(dtpm_cpu->cpu);
+	struct em_perf_state *table;
+	unsigned long freq;
+	u64 power;
+	int i, nr_cpus;
+
+	nr_cpus = cpumask_weight_and(cpu_online_mask, to_cpumask(pd->cpus));
+
+	rcu_read_lock();
+	table = em_perf_state_from_pd(pd);
+	for (i = 0; i < pd->nr_perf_states; i++) {
+
+		power = table[i].power * nr_cpus;
+
+		if (power > power_limit)
+			break;
+	}
+
+	freq = table[i - 1].frequency;
+	power_limit = table[i - 1].power * nr_cpus;
+	rcu_read_unlock();
+
+	freq_qos_update_request(&dtpm_cpu->qos_req, freq);
+
+	return power_limit;
+}
+
+static u64 scale_pd_power_uw(struct cpumask *pd_mask, u64 power)
+{
+	unsigned long max, sum_util = 0;
+	int cpu;
+
+	/*
+	 * The capacity is the same for all CPUs belonging to
+	 * the same perf domain.
+	 */
+	max = arch_scale_cpu_capacity(cpumask_first(pd_mask));
+
+	for_each_cpu_and(cpu, pd_mask, cpu_online_mask)
+		sum_util += sched_cpu_util(cpu);
+
+	return (power * ((sum_util << 10) / max)) >> 10;
+}
+
+static u64 get_pd_power_uw(struct dtpm *dtpm)
+{
+	struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
+	struct em_perf_state *table;
+	struct em_perf_domain *pd;
+	struct cpumask *pd_mask;
+	unsigned long freq;
+	u64 power = 0;
+	int i;
+
+	pd = em_cpu_get(dtpm_cpu->cpu);
+	if (!pd)
+		return 0;
+
+	pd_mask = em_span_cpus(pd);
+
+	freq = cpufreq_quick_get(dtpm_cpu->cpu);
+
+	rcu_read_lock();
+	table = em_perf_state_from_pd(pd);
+	for (i = 0; i < pd->nr_perf_states; i++) {
+
+		if (table[i].frequency < freq)
+			continue;
+
+		power = scale_pd_power_uw(pd_mask, table[i].power);
+		break;
+	}
+	rcu_read_unlock();
+
+	return power;
+}
+
+static int update_pd_power_uw(struct dtpm *dtpm)
+{
+	struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
+	struct em_perf_domain *em = em_cpu_get(dtpm_cpu->cpu);
+	struct em_perf_state *table;
+	int nr_cpus;
+
+	nr_cpus = cpumask_weight_and(cpu_online_mask, to_cpumask(em->cpus));
+
+	rcu_read_lock();
+	table = em_perf_state_from_pd(em);
+
+	dtpm->power_min = table[0].power;
+	dtpm->power_min *= nr_cpus;
+
+	dtpm->power_max = table[em->nr_perf_states - 1].power;
+	dtpm->power_max *= nr_cpus;
+
+	rcu_read_unlock();
+
+	return 0;
+}
+
+static void pd_release(struct dtpm *dtpm)
+{
+	struct dtpm_cpu *dtpm_cpu = to_dtpm_cpu(dtpm);
+	struct cpufreq_policy *policy;
+
+	if (freq_qos_request_active(&dtpm_cpu->qos_req))
+		freq_qos_remove_request(&dtpm_cpu->qos_req);
+
+	policy = cpufreq_cpu_get(dtpm_cpu->cpu);
+	if (policy) {
+		for_each_cpu(dtpm_cpu->cpu, policy->related_cpus)
+			per_cpu(dtpm_per_cpu, dtpm_cpu->cpu) = NULL;
+
+		cpufreq_cpu_put(policy);
+	}
+
+	kfree(dtpm_cpu);
+}
+
+static struct dtpm_ops dtpm_ops = {
+	.set_power_uw	 = set_pd_power_limit,
+	.get_power_uw	 = get_pd_power_uw,
+	.update_power_uw = update_pd_power_uw,
+	.release	 = pd_release,
+};
+
+static int cpuhp_dtpm_cpu_offline(unsigned int cpu)
+{
+	struct dtpm_cpu *dtpm_cpu;
+
+	dtpm_cpu = per_cpu(dtpm_per_cpu, cpu);
+	if (dtpm_cpu)
+		dtpm_update_power(&dtpm_cpu->dtpm);
+
+	return 0;
+}
+
+static int cpuhp_dtpm_cpu_online(unsigned int cpu)
+{
+	struct dtpm_cpu *dtpm_cpu;
+
+	dtpm_cpu = per_cpu(dtpm_per_cpu, cpu);
+	if (dtpm_cpu)
+		return dtpm_update_power(&dtpm_cpu->dtpm);
+
+	return 0;
+}
+
+static int __dtpm_cpu_setup(int cpu, struct dtpm *parent)
+{
+	struct dtpm_cpu *dtpm_cpu;
+	struct cpufreq_policy *policy;
+	struct em_perf_state *table;
+	struct em_perf_domain *pd;
+	char name[CPUFREQ_NAME_LEN];
+	int ret = -ENOMEM;
+
+	dtpm_cpu = per_cpu(dtpm_per_cpu, cpu);
+	if (dtpm_cpu)
+		return 0;
+
+	policy = cpufreq_cpu_get(cpu);
+	if (!policy)
+		return 0;
+
+	pd = em_cpu_get(cpu);
+	if (!pd || em_is_artificial(pd)) {
+		ret = -EINVAL;
+		goto release_policy;
+	}
+
+	dtpm_cpu = kzalloc_obj(*dtpm_cpu);
+	if (!dtpm_cpu) {
+		ret = -ENOMEM;
+		goto release_policy;
+	}
+
+	dtpm_init(&dtpm_cpu->dtpm, &dtpm_ops);
+	dtpm_cpu->cpu = cpu;
+
+	for_each_cpu(cpu, policy->related_cpus)
+		per_cpu(dtpm_per_cpu, cpu) = dtpm_cpu;
+
+	snprintf(name, sizeof(name), "cpu%d-cpufreq", dtpm_cpu->cpu);
+
+	ret = dtpm_register(name, &dtpm_cpu->dtpm, parent);
+	if (ret)
+		goto out_kfree_dtpm_cpu;
+
+	rcu_read_lock();
+	table = em_perf_state_from_pd(pd);
+	ret = freq_qos_add_request(&policy->constraints,
+				   &dtpm_cpu->qos_req, FREQ_QOS_MAX,
+				   table[pd->nr_perf_states - 1].frequency);
+	rcu_read_unlock();
+	if (ret < 0)
+		goto out_dtpm_unregister;
+
+	cpufreq_cpu_put(policy);
+	return 0;
+
+out_dtpm_unregister:
+	dtpm_unregister(&dtpm_cpu->dtpm);
+	dtpm_cpu = NULL;
+
+out_kfree_dtpm_cpu:
+	for_each_cpu(cpu, policy->related_cpus)
+		per_cpu(dtpm_per_cpu, cpu) = NULL;
+	kfree(dtpm_cpu);
+
+release_policy:
+	cpufreq_cpu_put(policy);
+	return ret;
+}
+
+static int dtpm_cpu_setup(struct dtpm *dtpm, struct device_node *np)
+{
+	int cpu;
+
+	cpu = of_cpu_node_to_id(np);
+	if (cpu < 0)
+		return 0;
+
+	return __dtpm_cpu_setup(cpu, dtpm);
+}
+
+static int dtpm_cpu_init(void)
+{
+	int ret;
+
+	/*
+	 * The callbacks at CPU hotplug time are calling
+	 * dtpm_update_power() which in turns calls update_pd_power().
+	 *
+	 * The function update_pd_power() uses the online mask to
+	 * figure out the power consumption limits.
+	 *
+	 * At CPUHP_AP_ONLINE_DYN, the CPU is present in the CPU
+	 * online mask when the cpuhp_dtpm_cpu_online function is
+	 * called, but the CPU is still in the online mask for the
+	 * tear down callback. So the power can not be updated when
+	 * the CPU is unplugged.
+	 *
+	 * At CPUHP_AP_DTPM_CPU_DEAD, the situation is the opposite as
+	 * above. The CPU online mask is not up to date when the CPU
+	 * is plugged in.
+	 *
+	 * For this reason, we need to call the online and offline
+	 * callbacks at different moments when the CPU online mask is
+	 * consistent with the power numbers we want to update.
+	 */
+	ret = cpuhp_setup_state(CPUHP_AP_DTPM_CPU_DEAD, "dtpm_cpu:offline",
+				NULL, cpuhp_dtpm_cpu_offline);
+	if (ret < 0)
+		return ret;
+
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "dtpm_cpu:online",
+				cpuhp_dtpm_cpu_online, NULL);
+	if (ret < 0)
+		return ret;
+
+	return 0;
+}
+
+static void dtpm_cpu_exit(void)
+{
+	cpuhp_remove_state_nocalls(CPUHP_AP_ONLINE_DYN);
+	cpuhp_remove_state_nocalls(CPUHP_AP_DTPM_CPU_DEAD);
+}
+
+struct dtpm_subsys_ops dtpm_cpu_ops = {
+	.name = KBUILD_MODNAME,
+	.init = dtpm_cpu_init,
+	.exit = dtpm_cpu_exit,
+	.setup = dtpm_cpu_setup,
+};