Subject: Re: Linux powerpc new system call instruction and ABI

From: Segher Boessenkool <[email-masked]>
Date: Wed, 19 May 2021 10:22:05 -0500

On Wed, May 19, 2021 at 03:06:49PM +0000, Joakim Tjernlund wrote:
> On Wed, 2021-05-19 at 09:38 -0500, Segher Boessenkool wrote:
> > On Wed, May 19, 2021 at 06:42:40PM +1000, Nicholas Piggin wrote:
> > > Excerpts from Joakim Tjernlund's message of May 19, 2021 6:08 pm:
> > > > I always figured the ppc way was superior. It begs the question if not the other archs should
> > > > change instead?
> > > 
> > > It is superior in some ways, not enough to be worth being different.
> > 
> > The PowerPC syscall ABI *requires* using cr0.3 for indicating errors,
> > you will have to do that whether you conflate the concepts of return
> > code and error indicator or not!
> > 
> > > Other archs are unlikely to change because it would be painful for
> > > not much benefit.
> > 
> > Other archs cannot easily change for much the same reason :-)
> 
> Really? I figured you could just add extra error indication in kernel syscall I/F.
> Eventually user space could migrate to the new indication.

You seem to assume all user space uses glibc, or *any* libc even?  This
is false.  Some programs do system calls directly.  Do not break the
kernel ABI :-)

Segher