[PATCH] change GLIBC PPC64/ELF2 ABI default to 2.17

[Joseph S. Myers]

On Wed, 29 Jan 2014, Adam Conrad wrote:

> > Not withstanding a double-double to IEEE binary128 transition which
> > the entire community would like to see happen as double-double is
> > very difficult to support and maintain.
> 
> This double-double transition rumour is something it would be nice to
> nail down as well, especially if it's something we can sort earlier
> than later, but it's also not as world-ending an ABI break as changing
> the baseline symbol version.

My position on that is that it should be considered a new ABI, with symbol 
versions set accordingly to the next glibc release after support is added; 
that supporting multiple long double variants, neither equivalent to 
double, in a single glibc build would be significantly worse than the 
existing compatibility support for configurations where long double 
changed from being equivalent to double.  (I don't rule out a merge of 
libquadmath support into glibc - which would mean two different 
floating-point formats with 16-byte size on x86_64 - given sufficient 
interest in TS 18661-3 support.  But that would involve different function 
names, e.g. cosl and cosf128, which is much less problematic than allowing 
for the same name possibly meaning two different functions.)

(A patch could of course demonstrate that support for two long double 
variants isn't as bad as I expect, but my starting assumption is as 
above.)

The existing work on binary128 on ppc64 is on 
svn://gcc.gnu.org/svn/gcc/branches/ibm/gcc-4_9-ieee/.

-- 
Joseph S. Myers
joseph@codesourcery.com