Re: [PATCH v7 5/6] powerpc/64: Make COMPAT user-selectable disabled on littleendian by default.

[Christophe Leroy]

On 09/02/2019 11:53 PM, Michael Ellerman wrote:
> Segher Boessenkool <segher@xxxxxxxxxxxxxxxxxxx> writes:
> > On Mon, Sep 02, 2019 at 12:03:12PM +1000, Michael Ellerman wrote:
> > > Michal Suchanek <msuchanek@xxxxxxx> writes:
> > > > On bigendian ppc64 it is common to have 32bit legacy binaries but much
> > > > less so on littleendian.
> > >
> > > I think the toolchain people will tell you that there is no 32-bit
> > > little endian ABI defined at all, if anything works it's by accident.
>                  ^
>                  v2
>
> > There of course is a lot of powerpcle-* support.  The ABI used for it
> > on linux is the SYSV ABI, just like on BE 32-bit.
>
> I was talking about ELFv2, which is 64-bit only. But that was based on
> me thinking we had a hard assumption in the kernel that ppc64le kernels
> always expect ELFv2 userland. Looking at the code though I was wrong
> about that, it looks like we will run little endian ELFv1 binaries,
> though I don't think anyone is testing it.
>
> > There also is specific powerpcle-linux support in GCC, and in binutils,
> > too.  Also, config.guess/config.sub supports it.  Half a year ago this
> > all built fine (no, I don't test it often either).
> >
> > I don't think glibc supports it though, so I wonder if anyone builds an
> > actual system with it?  Maybe busybox or the like?
> >
> > > So I think we should not make this selectable, unless someone puts their
> > > hand up to say they want it and are willing to test it and keep it
> > > working.
> >
> > What about actual 32-bit LE systems?  Does anyone still use those?
>
> Not that I've ever heard of.

We dropped support from 32-bit LE at least with a1f3ae3fe8a1 
("powerpc/32: Use stmw/lmw for registers save/restore in asm").

Discussion about it can be found at 
https://patchwork.ozlabs.org/patch/899465/

Christophe