cpu: Fix crash with empty -cpu option

Fix the following crash:

  $ qemu-system-x86_64 -cpu ''
  qemu-system-x86_64: qom/cpu.c:291: cpu_class_by_name: \
      Assertion `cpu_model && cc->class_by_name' failed.

Regression test script included.

Fixes: 99193d8f2ef5 ("cpu: drop unnecessary NULL check and cpu_common_class_by_name()")
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Message-Id: <20190418034501.5038-1-ehabkost@redhat.com>
Reviewed-by: Stefano Garzarella <sgarzare@redhat.com>
Tested-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/tests/acceptance/empty_cpu_model.py b/tests/acceptance/empty_cpu_model.py
new file mode 100644
index 0000000000..3f4f663582
--- /dev/null
+++ b/tests/acceptance/empty_cpu_model.py
@@ -0,0 +1,19 @@
+# Check for crash when using empty -cpu option
+#
+# Copyright (c) 2019 Red Hat, Inc.
+#
+# Author:
+#  Eduardo Habkost <ehabkost@redhat.com>
+#
+# This work is licensed under the terms of the GNU GPL, version 2 or
+# later.  See the COPYING file in the top-level directory.
+import subprocess
+from avocado_qemu import Test
+
+class EmptyCPUModel(Test):
+    def test(self):
+        cmd = [self.qemu_bin, '-S', '-display', 'none', '-machine', 'none', '-cpu', '']
+        r = subprocess.run(cmd, stderr=subprocess.PIPE, stdout=subprocess.PIPE)
+        self.assertEquals(r.returncode, 1, "QEMU exit code should be 1")
+        self.assertEquals(r.stdout, b'', "QEMU stdout should be empty")
+        self.assertNotEquals(r.stderr, b'', "QEMU stderr shouldn't be empty")