Re: Adding more ppc64 buildds from the POWER cloud
On Tue, Apr 05, 2016 at 08:32:28AM -0400, Lennart Sorensen wrote:
> On Tue, Apr 05, 2016 at 10:51:37AM +0200, Gabriel Paubert wrote:
> > What is really missing in ppc-land is a variant which uses 32 bit
> > addresses but otherwise knows that general purposes registers are
> > 64 bit wide and can be used as such, i.e., an alternative 32 bit ABI
> > which can only run on 64 bit processors and use 64 bit instructions
> > when beneficial while not needing over 4GB of address space.
> > (Truth be said, PPC code density is not great but much worse in
> > 64 bit mode than in 32 bit mode).
>
> Oh right the integer register width does change.
Yeah, I'm not even sure that the upper part of the GPR is properly
preserved across signal delivery for example.
Actuall a quick look at the code makes me think that they aren't, so
the upper 32 bit are not usable in practice.
>
> > I don't know for sure, but MIPS and/or Sparc may have something along
> > these lines.
>
> Well certainly mips has the old 32bit ABI, the 64 bit abi and the new
> 32 bit abi (64 bit instruction set and features running 32 bit mode).
> Very much like x86, x64 and x32,
x32 does not seem very popular. After all you are forced to use x64
addressing modes and coerce all addresses to below 4GB.
Anyway, I was more thinking along the line of the MIPS ABIs.
Gabriel
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