Re: Fun with trampolines

[alby.gamper@gmail.com]

On Saturday, March 17, 2018 at 5:05:14 AM UTC+11, Simon Wright wrote:
> alby.gamper@gmail.com writes:
> 
> > On Thursday, March 15, 2018 at 5:03:28 AM UTC+11, Simon Wright wrote:
> >> Some of you might be entertained by my recent encounter with trampolines
> >> for Tcl/Tk callbacks. Always tiresome when you visit demo code after a
> >> few years and it doesn't work any more.
> >> 
> >> There's at least a chance that the trampoline (which exists on the
> >> stack) might have been trampled on, though I didn't think so when I
> >> checked it. The question has to be, _which_ stack is it on? I suppose it
> >> has to be that of the code that's executing when 'Access is taken.
> >> 
> >> https://forward-in-code.blogspot.co.uk/2018/03/tcltk-vs-trampolines.html
> >
> > Dear Simon
> >
> > I seem to recall that GCC/GNAT recently (ie 7.1 or 7.2) removed support for
> > trampolines ? Could this have an effect on your legacy code ?
> >
> > Alex
> 
> Hi Alex,
> 
> I assume you mean FSF GCC 7.1.0, 7.2.0 rather than the
> similarly-numbered GNAT Pro releases?

Yes, I meant GCC 7.1

> 
> I don't think it's so much that they've removed support for trampolines
> as that they've worked out how to avoid using them! (FSF GCC 8.0.1 still
> generates them when it finds it necessary, i.e. some combination of
> nested & Convention => not-Ada).

Exactly

> 
> Thinking about it, since the trampoline is on the stack it's very
> dangerous to pass it to an external library for that library to call it
> much later! My only excuse is that it used to work ...