Re: java exception

[Yang Chang <yang at cs dot york dot ac dot uk>]

Thank you very much! But since gen_reg_rtx doesn't generate rtx for a 
specific register, how can the unwind functions know which register to 
store the reference to _Unwind_RaiseException?

cheers
yang

At 15:31 24/06/2005 -0400, you wrote:
> Yang Chang wrote:
>
> > I am trying to understand the GCJ implementation of Java exception 
> > mechanism. Currently, I am aware of that the GCJ compiler uses the return 
> > value of a "gen_reg_rtx(ptr_mode);"  (in function 
> > "get_exception_pointer") to represent something which holds a reference 
> > to an _Unwind_Exception struct and such a reference is passed to function 
> > _Unwind_RaiseException in libjava. However, I couldn't figure out how the 
> > two things map each other. I mean, how the _Unwind_RaiseException or some 
> > other lower level functions assign the aforementioned reference to what 
> > that rtx represents? and what that rtx really represents?
>
>
> The code you are looking at is used when generating an exception 
> _handler_. When the unwind mechanism gives control to the handler, the 
> exception object that was thrown needs to be passed to it somehow. 
> get_exception_pointer yields an RTL expression (in this case a REG, ie a 
> register) where a pointer to the _Unwind_Exception will be found. The 
> _Unwind_Exception will be put in that register by the unwinder before it 
> jumps into the handler. You'll want to look in gcc/unwind* and 
> libjava/exception.cc for the code for the unwinder itself.
>
> Bryce