Hi Jakub,
On Fri, 14 Jan 2022 15:31:43 +0100
Jakub Jelinek <jakub(a)redhat.com> wrote:
Another important thing I wanted to say is that we'd like to
switch
ppc64le from the numerically problematic IBM extended long double to
IEEE 754 quad long double. This is an ABI change. Some libraries
are already built so that they support both ABIs at the same time,
including glibc, libstdc++, libgcc, libgfortran etc.
For other libraries and binaries, the compiler, assembler and linker
will notice if they use long double and flag them as using either
IBM or IEEE long double and linker (or I think dynamic linker too)
might complain when things are mixed.
Right now the rawhide gcc still defaults to -mabi=ibmlongdouble
but the glibc/gcc libraries are built compatibly with both.
We'd like to configure gcc shortly before the mass rebuild with
--with-long-double-format=ieee so that it will default to
-mabi=ieeelongdouble, probably on a side-tag build first, and it
will be highly desirable to rebuild at least some of the most commonly
used library packages in the order of dependencies there, otherwise
I'd be afraid the mass rebuild could fail for way too many packages
(as the mass rebuild doesn't do dependency order rebuilds but just
goes through packages alphabetically or so).
Any suggestions on which packages have commonly used library packages
that use long double?
readelf -A on libraries on ppc64le prints either nothing (either
the library is thought not to use long double or supports both ABIs
transparently or hasn't been rebuilt for some years), or
Attribute Section: gnu
File Attributes
Tag_GNU_Power_ABI_FP: hard float, 128-bit IBM long double
for libraries (or binaries or object files) that use IBM long double
only or
Attribute Section: gnu
File Attributes
Tag_GNU_Power_ABI_FP: hard float, 128-bit IEEE long double
for IEEE long doubles.
So I think we want to rebuild on a side-tag packages that
provide shared libraries used by hundreds of other packages that
are
Tag_GNU_Power_ABI_FP: hard float, 128-bit IBM long double
right now.
a quick&dirty scan of /usr/lib64 on my F-34 workstation shows
many ./libQt5*
many ./libLLVM*
./libgobject-2.0
./libgio-2.0
./libglib-2.0
./libexiv2-xmp
./libhwy
./python3.9/site-packages/numpy/*
./libSDL2
./libiberty
./clang/12.0.1/lib/libclang_rt.builtins-powerpc64le.a
./ghdl/llvm/libgrt.a
./libc
as users of the Tag_GNU_Power_ABI_FP attribute. A vast majority of the
hits are "Tag_GNU_Power_ABI_FP: hard float, unspecified long double"
Translated to packages it is qt5-*, llvm + clang, numpy, SDL2, glib2,
exiv2, glibc, highway
Dan