Attached a simple patch that works. Though my knowledge of how this works is very limited so it might break something...
marc
--- /usr/bin/build-simple-cdd 2018-04-23 05:36:26.000000000 +0200 +++ ./build-simple-cdd 2019-05-27 18:47:26.177595431 +0200 @@ -532,8 +532,9 @@ if self.env.get("use_serial_console"): qemu_opts.append("-nographic") - # if [ -n "$mem" ]; then - # qemu_opts="$qemu_opts -m $mem" + if self.env.get("mem"): + qemu_opts.append("-m") + qemu_opts.append(self.env.get('mem')) # Hard disk image hd_img = os.path.join(self.env.get("simple_cdd_dir"), "qemu-test.hd.img")