The Designing And Implementing Of A Scripting Engine Based On Virtual Machine

With the development of script's technology, script has not only been applied in the edit of homepage. Many different functions of software can be combined together by making use of good interface of the script, and it comes to a powerful software product. In addition, because the script has the ability of transplanting other application program function, users can choose freely the function that they need to meet their demands. Currently, a lot of software systems support the script. But their support is not open. If you want to add one function to a script, you have to change a lot of codes of software .It make development so difficult and will bring influence on the security and stability of the software. In addition, slow execution of the script language will be bad to the performance of the software system. A virtual machine (VM) is independent of platforms, with characters of high performance, and security. Software that has been compiled by a compiler can be run on VM, and always plays high-performance on different platforms. So, a design and implementation of script engine based on VM has realized a real second-development. The script engine that based on VM comprises a 32-bit stack VM and a compiler which can dispose EPL language. When software compiled through EPL-compiler, the assembly codes come into being .And they can be executed on VM. VM is an unreal and abstract computer. It has a set of instructions and different storages. VM not only executes instructions but also operates on data, memory, and registers. It offers compiler a common interface on all platforms. If codes made by a compiler can be identified by VM, they can be carried out on VM. VM reloads instructions from bytecode files in the secondary memory and executes them. The principle of VM is: When VM gets into started on the command-line, it creates a error-log. Then, VM will dispose parameters of command-line and set up a executive environment and initialize according to the parameters of command-line. When executive environment built, VM begin to verify the bytecodes. When all the bytecodes are verified, VM will turn to the stage of execution. At the same time, VM is equipped with a debugger. A debugger can catch and analyze the leak of program. VM's debugger is designed to a bottom -tool ,and can observe and analyze the basic operation of VM.