Re: Implementing Exception Handling in a VM

Barry Kelly wrote:
> I'm presuming your VM is of the very simple, "while not Terminated do /
> case op of / opAdd: ... end" etc.


Correct.


> That depends on whether or not you've implemented procedure calls in
> your VM as Delphi procedure calls or as an explicit call stack.


I have an explicit call stack.


> To get an interpreter working using Delphi itself for exceptions, it
> would probably be easiest to recurse into the interpreter for the
> 'try..finally' and 'try..except' protected parts of your language.


This sounds interesting. I hadn't even thought of doing it this way.


> Doing it manually in the interpreter loop: the way you do it depends on
> what you want, but it basically involves walking up the call stack. [...]


Given the way the VM is currently written this may be the way to go.


> This means that your call stack needs to have a stack of exception
> information (i.e. handlers) associated with it somehow. You could put
> the exception info inside the call stack, in whatever structure you use
> for activation records (i.e. stack frames). Your 'try' statements need
> to compile into an instruction(s) which push handler info onto this
> stack, and you need to pop off that info for both the normal,
> no-exception route and the unwinding code.


Great--I understand what you're saying. The proof will be me coding it :-)


Thanks for taking the time to answer so fully, I really appreciate it.
I've managed to find plenty of literature on lexers, parsers, codegen,
and VMs, but very little on exception handling. Thanks again.


Cheers,
Mark.

Return to the comp.compilers page.
Search the comp.compilers archives again.