plugins: Ensure vCPU index is assigned in init/exit hooks

Since vCPUs are hashed by their index, this index can't
be uninitialized (UNASSIGNED_CPU_INDEX).

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Message-Id: <20240606124010.2460-2-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20240705084047.857176-28-alex.bennee@linaro.org>

plugins/core.c

@@ -245,6 +245,7 @@ void qemu_plugin_vcpu_init_hook(CPUState *cpu)
 {
     bool success;
 
+    assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
     qemu_rec_mutex_lock(&plugin.lock);
     plugin.num_vcpus = MAX(plugin.num_vcpus, cpu->cpu_index + 1);
     plugin_cpu_update__locked(&cpu->cpu_index, NULL, NULL);
@@ -263,6 +264,7 @@ void qemu_plugin_vcpu_exit_hook(CPUState *cpu)
 
     plugin_vcpu_cb__simple(cpu, QEMU_PLUGIN_EV_VCPU_EXIT);
 
+    assert(cpu->cpu_index != UNASSIGNED_CPU_INDEX);
     qemu_rec_mutex_lock(&plugin.lock);
     success = g_hash_table_remove(plugin.cpu_ht, &cpu->cpu_index);
     g_assert(success);