Re: Anyone fancy porting libffi to VAX?

[Dave McGuire <mcguire%neurotica.com@localhost>]

On 09/23/2013 05:08 PM, Jan-Benedict Glaw wrote:
> [libffi missing VAX support]
>>> Various software packages including glib2 default to depending
>>> on libffi.  Obviously the dependency can be disabled, omitting
>>> that functionality, but in case someone fancied a bit of VAX
>>> hacking I thought I'd mention it on this list :)
>> 
>> I think this is a great idea, but I don't think I can work on it.
>> I have a few balls in the air at the moment.
> 
> Did you, by any chance, have had time to work on it?

  Nope. :-(  The bad part of moving up here to the Pittsburgh area has
also been the BEST part.  I have more work than I've had in fifteen years!

> I'm currently trying to set-up an automated toolchain builder with
> a current version of NetBSD. It has a dependency on libffi (eg. 
> git->glib->libffi at least), so I've just started building some
> more unrelated dependencies and will have a look at libffi.
> 
> After all, VAX calling conventions are quite simple. Just push all
> 8, 16 and 32bit values onto the stack, the same for void pointer 
> and 64bit integers. (These seem to be mostly movq'ed, though),
> then calls the respective function address, along with the number
> of longwords (!) just pushed onto the stack (to unwind the stack 
> automatically on ret.)
> 
> So in comparison to a lot of other architectures/platforms/calling 
> conventions, where parameter distribution may be quite complex
> (eg. some in registers, others on stack, complex patterns of
> registers saved/restored during function call etc), VAX really is
> quite simple. The only exception is call-by-value with structs.
> Here, new stack space is allocated, copy the original struct
> (rounded up to full longwords), and calls with an appropriate
> number of longwords to be popped off the stack at return.

  It doesn't sound like it'll be a very tough problem to solve, at
first blush.

                  -Dave

-- 
Dave McGuire, AK4HZ
New Kensington, PA