On Fri, Jan 05, 2018 at 05:47:39PM +0000, Joseph Myers wrote: > On Fri, 5 Jan 2018, Jakub Jelinek wrote: > > > On Thu, Jan 04, 2018 at 06:05:55PM -0500, Michael Meissner wrote: > > > This patch is the beginning step to switching the PowerPC long double > > > support > > > from IBM extended double to IEEE 128-bit floating point on PowerPC > > > servers. It > > > will be necessary to have this patch or a similar patch to allow the > > > GLIBC team > > > to begin their modifications in GLIBC 2.28, so that by the time GCC 9 > > > comes > > > out, we can decide to switch the default. It is likely, the default will > > > only > > > be switched on the 64-bit little endian PowerPC systems, when a > > > distribution > > > goes through a major level, such that they can contemplate major changes. > > > > When you're mentioning multilibs, does that mean that we'll have two ABI > > incompatible libgcc.so.* libraries, two ABI incompatible libstdc++.so.* > > libraries etc.? Just one or 2 libc.so.*/libm.so.*? > > The existing GCC code tries to fix the libgcc function names so *tf* > always means IBM long double and *kf* always means IEEE long double. As > noted in my reply to this patch, I suspect it might fail to handle > __div?c3, __mul?c3 and __powi?c2 (at least) properly to avoid two > different libgcc ABIs there. > > I don't know the intent for libstdc++, libgfortran etc. - but it's been > stated the intent is a single set of glibc libraries. (Of course a > distribution probably has other libraries influenced by the long double > format in some way.)
It would have been much simpler if we didn't already have a 128-bit floating point type. But we had the existing long double support. In any case, even if you switch default long double format to IEEE, the kf/kc functions in libgcc will be called, even though the type is now TFmode/TCmode. It is unfortunate that the IBM extended double support did not define all of the interfaces to be __gcc_q<xxx>, but there were some tf/tc functions defined that are called, and I needed to pick unique names. -- Michael Meissner, IBM IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA email: meiss...@linux.vnet.ibm.com, phone: +1 (978) 899-4797
