plugins/core: allow reading of registers during discon events

We have protections that prevent callbacks that didn't declare
themselves as wanting to access registers. However for discontinuities
the system state is fully rectified so they should always be able to
read the register values.

a1688bc86c (plugins: add hooks for new discontinuity related callbacks)

Reviewed-by: Pierrick Bouvier <pierrick.bouvier@linaro.org>
Cc: Julian Ganz <neither@nut.email>
Reviewed-by: Julian Ganz <neither@nut.email>
Message-ID: <20251204194902.1340008-12-alex.bennee@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

plugins/core.c

@@ -119,6 +119,7 @@ static void plugin_vcpu_cb__discon(CPUState *cpu,
     struct qemu_plugin_cb *cb, *next;
     uint64_t to = cpu->cc->get_pc(cpu);
 
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_RW_REGS);
     if (cpu->cpu_index < plugin.num_vcpus) {
         /* iterate safely; plugins might uninstall themselves at any time */
         QLIST_FOREACH_SAFE_RCU(cb, &plugin.cb_lists[ev], entry, next) {
@@ -127,6 +128,7 @@ static void plugin_vcpu_cb__discon(CPUState *cpu,
             func(cb->ctx->id, cpu->cpu_index, type, from, to);
         }
     }
+    qemu_plugin_set_cb_flags(cpu, QEMU_PLUGIN_CB_NO_REGS);
 }
 
 /*