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Re: [PATCH, rs6000] ELFv2 ABI 1/8: Add options and infrastructure


On Tue, Nov 12, 2013 at 10:33:46PM +0000, Joseph S. Myers wrote:
> On Tue, 12 Nov 2013, Ulrich Weigand wrote:
> > Well, we had been thinking about this, but right now it seems we're not
> > going to be able to make that change throughout the ecosystem quickly
> > enough, so for now, it'll probably have to remain the IBM long double.
> 
> What's the difficulty?  GCC is supposed to support IEEE binary128 long 
> double already for Power, and IEEE binary128 works much better than IBM 
> long double in glibc.  The time a new ABI is being introduced is the time 
> to get things right rather than suggesting yet another ABI change in 
> future.

The major difficulty is that we don't want to use the existing
powerpc32 parameter passing and return scheme for ieee128 (ie. pass
pointers to memory).  The thought was to pass ieee128 in vsx
registers.  This means work in gcc, in glibc, in gdb, and likely other
places, and as Uli has already said, we have time and resource
constraints.

-- 
Alan Modra
Australia Development Lab, IBM


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