Date:	Fri, 23 Sep 94 18:37:19 -0600
From:	"Clifford T. Matthews" <iclone!faust!ctm AT sloth DOT swcp DOT com>
To:	djgpp AT sun DOT soe DOT clarkson DOT edu
Subject:	pascal calling conventions

Hi Folks,

Over here we've had to deal with pascal calling conventions for the few
years that we've had Macintosh emulator running in house.  Our first solution
was indeed to modify the compiler to support a pascal keyword.  Since
Michael Bushnell was working for us, and he's a monster programmer, he did
the work in two weeks and his solution worked exceedingly well.

However, since the FSF wasn't interested in incorporating our changes, we
didn't update our gcc as often as we'd like, because it always seemed to
make more sense to wait for a new release or two before we'd roll in our
mods, shake out any existing bugs and get on with our work.  Eventually we
decided to scrap the mods in favor of something more maintainable.

What we went was a couple of routines: PascalToCCall and CToPascalCall,
which take an additional argument that specifies what arguments are passed
in and the size of the return value, if any.  We then have some routines
that automatically figure out the magic numbers for all the routines that
we need to be able to access both as pascal and as C routines and because
we have to have pascal routine addresses, we also have some code that
generates some PascalToCCalls with the correct flags pushed on, so we can
then hand the addresses of these new glue routines to functions that expect
pascal function pointers.

Now we can use whatever the latest bug-free version of GCC is that we can
get our hands on, and we're in total control of the calling conventions,
which is important, because in addition to the pascal/C calling conventions
mentioned above, we also have a synthetic CPU to deal with so we also have
to interface between native routines and emulated 68k routines.

I'm not trying to tell others how to deal with similar issues, only telling
you what we used to do and what we currently do.  I doubt that the routines
we've come up with are directly useful to anyone but ourselves, but if 
anyone wants to look at them to get an idea of what we are doing, feel free
to send me e-mail and I'll try to excise enough of what we do for it to
make sense (although there's no documentation and we're also pretty busy
over here).

	--Cliff
	ctm AT ardi DOT com

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