Re: How do typical Ada calling conventions work ?

[Hadrien Grasland <hadrien.grasland@gmail.com>]

Le vendredi 21 août 2015 14:47:05 UTC+2, Niklas Holsti a écrit :
> On 15-08-21 13:41 , Markus Schöpflin wrote:
> > Am 21.08.2015 um 10:37 schrieb Hadrien Grasland:
> >
> >> Does someone know how typical Ada implementations manage to cope with
> >> this, and if it varies a lot from one implementation to another ?
> >
> > GNAT allocates such objects on the secondary stack. Quote from the user
> > guide:
> >
> > ---%<---
> > `-Dnn[k|m]'
> > This switch can be used to change the default secondary stack size value
> > to a specified size nn, which is expressed in bytes by default, or in
> > kilobytes when suffixed with k or in megabytes when suffixed with m.
> >
> > The secondary stack is used to deal with functions that return a
> > variable sized result, for example a function returning an unconstrained
> > String. There are two ways in which this secondary stack is allocated.
> >
> > For most targets, the secondary stack is growing on demand and is
> > allocated as a chain of blocks in the heap. The -D option is not very
> > relevant. It only give some control over the size of the allocated
> > blocks (whose size is the minimum of the default secondary stack size
> > value, and the actual size needed for the current allocation request).
> >
> > For certain targets, notably VxWorks 653, the secondary stack is
> > allocated by carving off a fixed ratio chunk of the primary task stack.
> > The -D option is used to define the size of the environment task's
> > secondary stack.
> > --->%---
> 
> I stumbled across an interesting, old discussion about GNAT's approach 
> (it seems a secondary stack was not the initial choice) with references 
> to some other compilers:
> 
> http://computer-programming-forum.com/44-ada/2227f74c82f45451.htm
> 
> 
> -- 
> Niklas Holsti
> Tidorum Ltd
> niklas holsti tidorum fi
>        .      @       .

Thanks for your answers ! These are some pretty nice ways to do it instead indeed.

I'm glad the secondary stack approach won in the end for GNAT, it sounds more efficient, clean and scalable than what they were attempting in the beginning.

Hadrien