Re: [Libffcall] Return small structs in registers for powerpc on openbsd

[Josh Elsasser]

On Thu, Oct 17, 2019 at 11:29:05PM +0200, Bruno Haible wrote:
> Hi Josh,
> 
> Thank you for the patch.
> It will take me a while to make sure your patch is good, and include it.

Of course, thanks for taking the time to look.

> Maybe you can help me with some infos:
>   - Which OpenBSD version and which qemu-system-ppc or qemu-system-ppc64
>     options do you recommend for running it in a VM?

I've never tried that before, I'll poke around and see if I can find a
working configuration.

>   - If gcc 4.1.2 needs patches, to make it compile, maybe a different
>     version is simpler to use. How about using gcc 4.2.4 instead?

I'll give 4.2.4 a try.

>   - Do you have a formal documentation of the "secure plt ABI"?

This is the reference I was reading:

https://www.polyomino.org.uk/publications/2011/Power-Arch-32-bit-ABI-supp-1.0-Unified.pdf

I also found this helpful:

http://www.sourceware.org/ml/binutils/2005-05/txt00011.txt

> > Replace the unused powerpc small-struct-copying code with hppa's,
> > which copies structs of all sizes.
> 
> Oh really? I thought that the hppa code for small structs was so braindead
> that it would remain the only OS that needs this code. The code for
> m68k, s390, sparc is simpler.

The existing code doesn't handle 3, 5, 6, or 7 byte structs. It looks
like riscv uses the hppa code too. I wonder if the compiler pads
structs to a full word on those other platforms?

> Bruno