I committed the following patch today. After a burn-in period, I plan to
commit the patch to older GCC releases, and close out the two PRs.
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 <meiss...@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.
---
libgcc/config/rs6000/t-linux | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/libgcc/config/rs6000/t-linux b/libgcc/config/rs6000/t-linux
index ed821947b66..72e9c2770a6 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
--
2.22.0
--
Michael Meissner, IBM
IBM, M/S 2506R, 550 King Street, Littleton, MA 01460-6245, USA
email: meiss...@linux.ibm.com, phone: +1 (978) 899-4797
