PowerPC: PR libgcc/97543 and libgcc/97643, fix long double issues

If you use a compiler with long double defaulting to 64-bit instead of 128-bit
with IBM extended double, you get linker warnings about mis-matches in the gnu
attributes for long double (PR libgcc/97543).  Even if the compiler is
configured to have long double be 64 bit as the default with the configuration
option '--without-long-double-128' you get the warnings.

You also get the same issues if you use a compiler with long double defaulting
to IEEE 128-bit instead of IBM extended double (PR libgcc/97643).

The issue is the way libgcc.a/libgcc.so is built.  Right now when building
libgcc under Linux, the long double size is set to 128-bits when building
libgcc.  However, the gnu attributes are set, leading to the warnings.

One feature of the current GNU attribute implementation is if you have a shared
library (such as libgcc_s.so), the GNU attributes for the shared library is an
inclusive OR of all of the objects within the library.  This means if any
object file that uses the -mlong-double-128 option and uses long double, the GNU
attributes for the library will indicate that it uses 128-bit IBM long
doubles.  If you have a static library, you will get the warning only if you
actually reference an object file  with the attribute set.

This patch does two things:

    1)	All of the object files that support IBM 128-bit long doubles
	explicitly set the ABI to IBM extended double.

    2)	I turned off GNU attributes for building the shared library or for
        building the IBM 128-bit long double support.

libgcc/
2020-12-03  Michael Meissner  <meissner@linux.ibm.com>

	PR libgcc/97543
	PR libgcc/97643
	* config/rs6000/t-linux (IBM128_STATIC_OBJS): New make variable.
	(IBM128_SHARED_OBJS): New make variable.
	(IBM128_OBJS): New make variable.  Set all objects to use the
	explicit IBM format, and disable gnu attributes.
	(IBM128_CFLAGS): New make variable.
	(gcc_s_compile): Add -mno-gnu-attribute to all shared library
	modules.

1 files changed, 22 insertions, 0 deletions

diff --git a/libgcc/config/rs6000/t-linux b/libgcc/config/rs6000/t-linux
index ed82194..72e9c27 100644
--- a/libgcc/config/rs6000/t-linux
+++ b/libgcc/config/rs6000/t-linux
@@ -6,3 +6,25 @@ HOST_LIBGCC2_CFLAGS += -mlong-double-128
 # smaller and faster libgcc code.  Directly specifying -mcmodel=small
 # would need to take into account targets for which -mcmodel is invalid.
 HOST_LIBGCC2_CFLAGS += -mno-minimal-toc
+
+# On the modules that deal with IBM 128-bit values, make sure that TFmode uses
+# the IBM extended double format.  Also turn off gnu attributes on the static
+# modules.
+IBM128_STATIC_OBJS	= ibm-ldouble$(objext) _powitf2$(objext) \
+			  ppc64-fp$(objext) _divtc3$(object) _multc3$(object) \
+			  _fixtfdi$(object) _fixunstfdi$(object) \
+	                  _floatditf$(objext) _floatunsditf$(objext)
+IBM128_SHARED_OBJS	= $(IBM128_STATIC_OBJS:$(objext):_s$(objext))
+IBM128_OBJS		= $(IBM128_STATIC_OBJS) $(IBM128_SHARED_OBJS)
+
+IBM128_CFLAGS		= -Wno-psabi -mabi=ibmlongdouble -mno-gnu-attribute
+
+$(IBM128_OBJS) : INTERNAL_CFLAGS += $(IBM128_CFLAGS)
+
+# Turn off gnu attributes for long double size on all of the shared library
+# modules, but leave it on for the static modules, except for the functions
+# that explicitly process IBM 128-bit floating point.  Shared libraries only
+# have one gnu attribute for the whole library, and it can lead to warnings if
+# somebody changes the long double format.  We leave it on for the static
+# modules to catch mis-compilation errors.
+gcc_s_compile += -mno-gnu-attribute