[RFC PATCH v3 04/11] contrib/plugins: add plugin showcasing new dicontinuity related API

[Julian Ganz <neither@nut.email>]

We recently introduced new plugin API for registration of discontinuity
related callbacks. This change introduces a minimal plugin showcasing
the new API. It simply counts the occurances of interrupts, exceptions
and host calls per CPU and reports the counts when exitting.
---
 contrib/plugins/meson.build |  3 +-
 contrib/plugins/traps.c     | 96 +++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+), 1 deletion(-)
 create mode 100644 contrib/plugins/traps.c

diff --git a/contrib/plugins/meson.build b/contrib/plugins/meson.build
index 63a32c2b4f..9a3015e1c1 100644
--- a/contrib/plugins/meson.build
+++ b/contrib/plugins/meson.build
@@ -1,5 +1,6 @@
 contrib_plugins = ['bbv', 'cache', 'cflow', 'drcov', 'execlog', 'hotblocks',
-                   'hotpages', 'howvec', 'hwprofile', 'ips', 'stoptrigger']
+                   'hotpages', 'howvec', 'hwprofile', 'ips', 'stoptrigger',
+                   'traps']
 if host_os != 'windows'
   # lockstep uses socket.h
   contrib_plugins += 'lockstep'
diff --git a/contrib/plugins/traps.c b/contrib/plugins/traps.c
new file mode 100644
index 0000000000..ecd4beac5f
--- /dev/null
+++ b/contrib/plugins/traps.c
@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2024, Julian Ganz <neither@nut.email>
+ *
+ * Traps - count traps
+ *
+ * License: GNU GPL, version 2 or later.
+ *   See the COPYING file in the top-level directory.
+ */
+
+#include <stdio.h>
+
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+
+typedef struct {
+    uint64_t interrupts;
+    uint64_t exceptions;
+    uint64_t hostcalls;
+    bool active;
+} TrapCounters;
+
+static struct qemu_plugin_scoreboard *traps;
+static size_t max_vcpus;
+
+static void vcpu_init(qemu_plugin_id_t id, unsigned int vcpu_index)
+{
+    TrapCounters* rec = qemu_plugin_scoreboard_find(traps, vcpu_index);
+    rec->active = true;
+}
+
+static void vcpu_discon(qemu_plugin_id_t id, unsigned int vcpu_index,
+                        enum qemu_plugin_discon_type type, uint64_t from_pc,
+                        uint64_t to_pc)
+{
+    TrapCounters* rec = qemu_plugin_scoreboard_find(traps, vcpu_index);
+    switch (type) {
+    case QEMU_PLUGIN_DISCON_INTERRUPT:
+        rec->interrupts++;
+        break;
+    case QEMU_PLUGIN_DISCON_EXCEPTION:
+        rec->exceptions++;
+        break;
+    case QEMU_PLUGIN_DISCON_HOSTCALL:
+        rec->hostcalls++;
+        break;
+    default:
+        /* unreachable */
+        break;
+    }
+}
+
+static void plugin_exit(qemu_plugin_id_t id, void *p)
+{
+    g_autoptr(GString) report;
+    report = g_string_new("VCPU, interrupts, exceptions, hostcalls\n");
+    int vcpu;
+
+    for (vcpu = 0; vcpu < max_vcpus; vcpu++) {
+        TrapCounters *rec = qemu_plugin_scoreboard_find(traps, vcpu);
+        if (rec->active) {
+            g_string_append_printf(report,
+                                   "% 4d, % 10"PRId64", % 10"PRId64", % 10"
+                                   PRId64"\n",
+                                   vcpu,
+                                   rec->interrupts, rec->exceptions,
+                                   rec->hostcalls);
+        }
+    }
+
+    qemu_plugin_outs(report->str);
+    qemu_plugin_scoreboard_free(traps);
+}
+
+QEMU_PLUGIN_EXPORT
+int qemu_plugin_install(qemu_plugin_id_t id, const qemu_info_t *info,
+                        int argc, char **argv)
+{
+    if (!info->system_emulation) {
+        fputs("trap plugin can only be used in system emulation mode.\n",
+              stderr);
+        return -1;
+    }
+
+    max_vcpus = info->system.max_vcpus;
+    traps = qemu_plugin_scoreboard_new(sizeof(TrapCounters));
+    qemu_plugin_register_vcpu_init_cb(id, vcpu_init);
+    qemu_plugin_vcpu_for_each(id, vcpu_init);
+
+    qemu_plugin_register_vcpu_discon_cb(id, QEMU_PLUGIN_DISCON_TRAPS,
+                                        vcpu_discon);
+
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+
+    return 0;
+}
-- 
2.45.2