Re: Questions about trampolines

[Joern RENNECKE <joern dot rennecke at st dot com>]

Clifford Wolf wrote:

> Hi,
>
> On Wed, Mar 16, 2005 at 01:50:32PM +0000, Joern RENNECKE wrote:
>  
>
> > These can be provided in a separate module of the static libgcc, together
> > with allocation and deallocation of individual trampolines from the pool
> > (the latter has to be called from the epilogue of functions that use
> > initialize (and thus allocate) trampolines).
> >    
>
> I also thought about that already.
> It's a good idea, but not good enough.  :-(
>
> what's about longjmp(), gotos from nested functions to their surrounding
> functions (with a complex calltree inbetween) and (c++) exceptions?
>
> always preserving frame pointers, unrolling the stack frame by frame and
> executing this epilogues might be possible - but I don't think that we
> really want to go this way..

In a single-threaded environment, you treat the trampoline pool as a 
stack, and
when you allocate a new one, check first if there are any trampolines 
left at the
top that have a static chain pointer that points into deallocated data 
stack.

In (possibly) multithreaded environments, you could treat the 
trampolines as objects
with a destructor.  Exception handling already knows how to call 
destructors while
unwinding the stack.