On Mon, Jan 03, 2022 at 11:19:21AM +0100, Thomas Koenig wrote:
> > > If you are building libraries that contain modules with multiple
> > > long double
> > > types, you must use the '-mno-gnu-attribute'. We also use the
> > > '-Wno-psabi'
> > > option, which silences the warning that you are switching long
> > > double types (if
> > > glibc is not 2.34 or newer). We may need to tweak -Wno-psabi for
> > > use with
> > > Fortran.
> >
> > I am now at the point where the object files are also compiled correctly
> > for the gfortran specifics:
> >
> > 0000000000000000 <_gfortran_specific__abs_r17>:
> > 0: 09 00 43 f4 lxv vs34,0(r3)
> > 4: 48 16 40 fc xsabsqp v2,v2
> > 8: 20 00 80 4e blr
> >
> > However, the linker complains, as you said it would, about the different
> > formats:
> >
> > /opt/at15.0/bin/ld: .libs/maxloc0_4_r16.o uses IBM long double,
> > .libs/_abs_r17.o uses IEEE long double
> > /opt/at15.0/bin/ld: failed to merge target specific data of file
> > .libs/_abs_r17.o
> >
> > I know next to nothing about libtool, so I do not know how to
> > add the flags so the linker can find them.
> >
> > Any pointers?
>
> One additional point. The linker does not understand
> -mno-gnu-attribute:
>
> $ /opt/at15.0/bin/ld -mno-gnu-attribute
> /opt/at15.0/bin/ld: unrecognised emulation mode: no-gnu-attribute
> Supported emulations: elf64lppc elf32lppc elf32lppclinux elf32lppcsim
> elf64ppc elf32ppc elf32ppclinux elf32ppcsim
>
> So, waiting for info to proceed.
-mno-gnu-attribute isn't a linker flag, but a compiler flag.
And e.g. libstdc++ configure uses it while compiling itself on
powerpc*linux:
LONG_DOUBLE_COMPAT_FLAGS="$LONG_DOUBLE_COMPAT_FLAGS -mno-gnu-attribute"
# Check for IEEE128 support in libm:
AC_CHECK_LIB(m, __frexpieee128,
[ac_ldbl_ieee128_in_libc=yes],
[ac_ldbl_ieee128_in_libc=no])
if test $ac_ldbl_ieee128_in_libc = yes; then
# Determine which long double format is the compiler's default:
AC_TRY_COMPILE(, [
#ifndef __LONG_DOUBLE_IEEE128__
#error compiler defaults to ibm128
#endif
], [ac_ldbl_ieee128_default=yes], [ac_ldbl_ieee128_default=no])
# Library objects should use default long double format.
if test "$ac_ldbl_ieee128_default" = yes; then
LONG_DOUBLE_128_FLAGS="-mno-gnu-attribute"
# Except for the ones that explicitly use these flags:
LONG_DOUBLE_ALT128_COMPAT_FLAGS="-mabi=ibmlongdouble
-mno-gnu-attribute -Wno-psabi"
else
LONG_DOUBLE_128_FLAGS="-mno-gnu-attribute"
LONG_DOUBLE_ALT128_COMPAT_FLAGS="-mabi=ieeelongdouble
-mno-gnu-attribute -Wno-psabi"
fi
AC_DEFINE([_GLIBCXX_LONG_DOUBLE_ALT128_COMPAT],1,
[Define if compatibility should be provided for alternative
128-bit long double formats.])
port_specific_symbol_files="$port_specific_symbol_files
\$(top_srcdir)/config/os/gnu-linux/ldbl-ieee128-extra.ver"
ac_ldbl_alt128_compat=yes
else
ac_ldbl_alt128_compat=no
fi
;;
The idea behind this is that libstdc++ is written such that it can handle
both IBM extended and IEEE quad long double, so its object files are
compatible with both.
So I think we want:
2022-01-03 Jakub Jelinek <ja...@redhat.com>
* configure.ac (Use -mno-gnu-attribute together with
-mabi=ibmlongdouble or -mabi=ieeelongdouble.
--- libgfortran/configure.ac 2021-12-31 11:08:19.032835533 +0000
+++ libgfortran/configure.ac 2022-01-03 10:32:16.927834682 +0000
@@ -163,9 +163,9 @@ if test "x$GCC" = "xyes"; then
#error long double is double
#endif]],
[[(void) 0;]])],
- [AM_FCFLAGS="$AM_FCFLAGS -mabi=ibmlongdouble";
- AM_CFLAGS="$AM_CFLAGS -mabi=ibmlongdouble";
- CFLAGS="$CFLAGS -mabi=ibmlongdouble";
+ [AM_FCFLAGS="$AM_FCFLAGS -mabi=ibmlongdouble -mno-gnu-attribute";
+ AM_CFLAGS="$AM_CFLAGS -mabi=ibmlongdouble -mno-gnu-attribute";
+ CFLAGS="$CFLAGS -mabi=ibmlongdouble -mno-gnu-attribute";
have_real_17=yes])
;;
*)
Jakub
