https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103623
--- Comment #6 from Bill Schmidt <wschmidt at gcc dot gnu.org> --- With a quick and dirty patch to implement this, I get: $ /home/wschmidt/gcc/build/gcc-e300/gcc/xgcc -c -O2 pr103623.c -B/home/wschmidt/gcc/build/gcc-e300/gcc -mcpu=401 pr103623.c: In function 'main': pr103623.c:2:16: error: '__builtin_unpack_longdouble' requires long double to be IBM 128-bit format 2 | #define UNPACK __builtin_unpack_longdouble | ^ pr103623.c:11:15: note: in expansion of macro 'UNPACK' 11 | double x0 = UNPACK (a, 0); | ^~~~~~ Arseny, does this properly diagnose the issue for you?