ppc64le and 32-bit LE userland compatibility

[Daniel Kolesa]

On Tue, Jun 2, 2020, at 01:55, Joseph Myers wrote:
> On Mon, 1 Jun 2020, Joseph Myers wrote:
> 
> > The minimum supported architecture for powerpc64le (POWER8) has VSX.  My 
> > understanding was that the suggestion was for 32-bit userspace to run 
> > under powerpc64le kernels running on POWER8 or later, meaning that such a 
> > 32-bit LE port, and any ABI designed for such a port, can assume VSX is 
> > available.  Or does VSX not work, at the hardware level, for 32-bit 
> > POWER8?  (In which case you could pick another ABI for binary128 argument 
> > passing and return.)
> 
> In fact, my understanding is that the ABI for passing binary128 values in 
> vector registers is perfectly implementable for processors with just VMX 
> (AltiVec) and not VSX.  So if you do want to support binary128 for a new 
> ABI for either 32-bit LE or 32-bit or 64-bit BE, you don't need to require 
> VSX for that ABI, you just need to change any GCC requirement for VSX for 
> binary128 to allow it with VMX when building for your new ABI.

Which still doesn't help us even if true, since we plan to support hardware that doesn't have any kind of vector functionality in the first place (PowerPC G3/G4, and for the ELFv2 64-bit BE port, the minimum for binary packages is 970/G5 which does have AltiVec, but it is also supported to build your userland from source without this, for e.g. POWER5 machines, or e5500 SoCs)

> 
> -- 
> Joseph S. Myers
> joseph at codesourcery.com
>