vl.c: Exit QEMU early if no machine is found

We check whether the variable machine is NULL or not before accessing
it. If machine is NULL, exit QEMU with an error, this can avoids a
segfault error.

Markus Armbruster <armbru@redhat.com> adds that the segfault can be
reproduced as follows:

  $ qemu-system-xtensa -cpu help

Signed-off-by: Dunrong Huang <riegamaths@gmail.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>

1 files changed, 5 insertions, 5 deletions

diff --git a/vl.c b/vl.c
index a4a520fb7e..4871428864 100644
--- a/vl.c
+++ b/vl.c
@@ -3204,6 +3204,11 @@ int main(int argc, char **argv, char **envp)
     }
     loc_set_none();
 
+    if (machine == NULL) {
+        fprintf(stderr, "No machine found.\n");
+        exit(1);
+    }
+
     if (machine->hw_version) {
         qemu_set_version(machine->hw_version);
     }
@@ -3246,11 +3251,6 @@ int main(int argc, char **argv, char **envp)
         data_dir = CONFIG_QEMU_DATADIR;
     }
 
-    if (machine == NULL) {
-        fprintf(stderr, "No machine found.\n");
-        exit(1);
-    }
-
     /*
      * Default to max_cpus = smp_cpus, in case the user doesn't
      * specify a max_cpus value.