Re: libgfortran.so SONAME and powerpc64le-linux ABI changes

[Michael Meissner <meissner@linux.ibm.com>]

I've played with some patches to PowerPC to set the defaults for fortran.  But
without doing a full rebuild like you would do with a new distribution, I think
it will be problematical, unless you build everything with the default long
double set to IEEE 128-bit.

First off all, libquadmath is currently built on Linux 64-bit systems.  I never
removed building libquadmath once we got the official glibc 2.34 support

So to go in more detail of what I've tried.

I added an undocumented switch -mfortran that says set the defaults for
Fortran.  This switch would be used to build libgfortran, and also set with
TARGET_F951_OPTIONS for all Fortran invocations.

I tried to switch to float128_type_node instead of long_double_type_node.  I
ran into problems with gimplify in that it could not do a conversion from
_Float128 to float.  I suspect I didn't actually use the right type.

I then went to patches where -mfortran silently switches the long double type
to IEEE 128-bit.  There you get into various compatibility issues where the
linker complains that you are calling between the different long double types.

For instance because we are still building libquadmath, libquadmath is marked
as having long double being IBM 128-bit, but it is called from Fortran modules
that have long double being IEEE 128-bit.  I then did a build supressing
building libquadmath since I was using LE with glibc 2.34, and I got much
further.  This time instead of a lot of failures, I got 29 failures, due to
libgfortran still being marked as IBM long double and the fortran modules are
marked as IEEE long double.

Right now, the only way to avoid these things is to build the entire toolchain
defaulting to IEEE 128-bit.

-- 
Michael Meissner, IBM
PO Box 98, Ayer, Massachusetts, USA, 01432
email: meissner@linux.ibm.com