ppc64le and 32-bit LE userland compatibility

[Michal Suchánek]

On Tue, Jun 02, 2020 at 05:40:39PM +0200, Daniel Kolesa wrote:
> 
> 
> On Tue, Jun 2, 2020, at 17:27, Michal Suchánek wrote:
> > On Tue, Jun 02, 2020 at 05:13:25PM +0200, Daniel Kolesa wrote:
> > > On Tue, Jun 2, 2020, at 16:23, Michal Suchánek wrote:
> > > > On Tue, Jun 02, 2020 at 01:40:23PM +0000, Joseph Myers wrote:
> > > > > On Tue, 2 Jun 2020, Daniel Kolesa wrote:
> > > > > 
> > > > > > not be limited to being just userspace under ppc64le, but should be 
> > > > > > runnable on a native kernel as well, which should not be limited to any 
> > > > > > particular baseline other than just PowerPC.
> > > > > 
> > > > > This is a fairly unusual approach to bringing up a new ABI.  Since new 
> > > > > ABIs are more likely to be used on new systems rather than switching ABI 
> > > > > on an existing installation, and since it can take quite some time for all 
> > > > > the software support for a new ABI to become widely available in 
> > > > > distributions, people developing new ABIs are likely to think about what 
> > > > > new systems are going to be relevant in a few years' time when working out 
> > > > > the minimum hardware requirements for the new ABI.  (The POWER8 minimum 
> > > > > for powerpc64le fits in with that, for example.)
> > > > That means that you cannot run ppc64le on FSL embedded CPUs (which lack
> > > > the vector instructions in LE mode). Which may be fine with you but
> > > > other people may want to support these. Can't really say if that's good
> > > > idea or not but I don't foresee them going away in a few years, either.
> > > 
> > > well, ppc64le already cannot be run on those, as far as I know (I don't think it's possible to build ppc64le userland without VSX in any configuration)
> > 
> > What hardware are you targetting then? I did not notice anything
> > specific mentioned in the thread.
> > 
> > Naturally on POWER the first cpu that has LE support is POWER8 so you
> > can count on all other POWER8 features to be present. With other
> > architecture variants the situation is different.
> 
> This is not true; nearly every 32-bit PowerPC CPU has LE support (all the way back to 6xx), these would be the native-hardware targets for the port (would need kernel support implemented, but it's technically possible).
I find dealing with memory management issues on 32bit architectures a
pain. There is never enough address space.
> 
> As far as 64-bit CPUs go, POWER7 is the first one that could in practice run the current ppc64le configuration, but in glibc it's limited to POWER8 and in gcc the default for powerpc64le is also POWER8 (however, it is perfectly possible to configure gcc for POWER7 and use musl libc with it).
That's interesting. I guess I was tricked but the glibc limitation.

Thanks

Michal