[PATCH] plugins: new syscalls plugin

[Matthias Weckbecker <matthias@weckbecker.name>]

This commit adds a new syscalls plugin that displays the syscalls
as they are executed and returned. This plugin outputs the number
of the syscall as well as the syscall return value.

Works in *-user only.

Essentially, this commit restores:

  https://lists.gnu.org/archive/html/qemu-devel/2018-06/msg00846.html

by using the new QEMU plugin API.

Signed-off-by: Matthias Weckbecker <matthias@weckbecker.name>
---
 tests/plugin/Makefile  |  1 +
 tests/plugin/syscall.c | 49 ++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+)
 create mode 100644 tests/plugin/syscall.c

diff --git a/tests/plugin/Makefile b/tests/plugin/Makefile
index e9348fde4a..fc176909e9 100644
--- a/tests/plugin/Makefile
+++ b/tests/plugin/Makefile
@@ -21,6 +21,7 @@ NAMES += hotblocks
 NAMES += howvec
 NAMES += hotpages
 NAMES += lockstep
+NAMES += syscall
 
 SONAMES := $(addsuffix .so,$(addprefix lib,$(NAMES)))
 
diff --git a/tests/plugin/syscall.c b/tests/plugin/syscall.c
new file mode 100644
index 0000000000..53ee2ab6c4
--- /dev/null
+++ b/tests/plugin/syscall.c
@@ -0,0 +1,49 @@
+/*
+ * Copyright (C) 2020, Matthias Weckbecker <matthias@weckbecker.name>
+ *
+ * License: GNU GPL, version 2 or later.
+ *   See the COPYING file in the top-level directory.
+ */
+#include <inttypes.h>
+#include <assert.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <stdio.h>
+#include <glib.h>
+
+#include <qemu-plugin.h>
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_version = QEMU_PLUGIN_VERSION;
+
+static void vcpu_syscall(qemu_plugin_id_t id, unsigned int vcpu_index,
+                         int64_t num, uint64_t a1, uint64_t a2,
+                         uint64_t a3, uint64_t a4, uint64_t a5,
+                         uint64_t a6, uint64_t a7, uint64_t a8)
+{
+    g_autofree gchar *out = g_strdup_printf("syscall #%" PRIi64 "\n", num);
+    qemu_plugin_outs(out);
+}
+
+static void vcpu_syscall_ret(qemu_plugin_id_t id, unsigned int vcpu_idx,
+                             int64_t num, int64_t ret)
+{
+    g_autofree gchar *out;
+    out = g_strdup_printf("syscall #%" PRIi64 " returned -> %" PRIi64 "\n",
+            num, ret);
+    qemu_plugin_outs(out);
+}
+
+/* ************************************************************************* */
+
+static void plugin_exit(qemu_plugin_id_t id, void *p) {}
+
+QEMU_PLUGIN_EXPORT int qemu_plugin_install(qemu_plugin_id_t id,
+                                           const qemu_info_t *info,
+                                           int argc, char **argv)
+{
+    qemu_plugin_register_vcpu_syscall_cb(id, vcpu_syscall);
+    qemu_plugin_register_vcpu_syscall_ret_cb(id, vcpu_syscall_ret);
+    qemu_plugin_register_atexit_cb(id, plugin_exit, NULL);
+    return 0;
+}
-- 
2.23.0