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.
9f1a650199