AIX provides two versions of long double and declares all of the C99 long double symbols in math.h header file. One implementation aliases long double to IEEE double precision type and the other implementation aliases long double to IBM's paired double format. All of the C99 symbols for IEEE double precision are implemented in libm, but not all of the C99 symbols for the IBM long double format are implemented.
IBM's proprietary XL compiler (cc, xlc) defaults to IEEE double precision and provides a special invocation to default to IBM long double (cc128, xlc128). GNU/Linux and GCC on GNU/Linux default to IEEE quad precision long double. Because the long double choice is an ABI change, GCC on AIX switched to GNU/Linux compatibility with support for AIX 6.1, before the incomplete implementation was noticed. This mostly worked until libgfortran started using additional C99 functions, causing GCC Bugzilla [target/47032] libgfortran references complex long double functions missing on AIX libstdc++-v3 on AIX builds with AIX long double support, although user programs that try to access the missing functions (copysign, nextafter, etc.) will experience link-time failures. libgfortran on AIX fails to build with AIX long double support because it accesses the missing functions in its implementation. I would like to solicit feedback about how to proceed: Should GCC on AIX revert back to 64 bit long double size, allowing all libraries to build and work, but breaking GCC/G++ ABI on AIX? Or should it continue to utilize 128 bit long double, building libstdc++-v3 that works if the user program does not utilize the missing symbols and fails to build libgfortran? Thanks, David
