http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53383
--- Comment #13 from Jan Hubicka <hubicka at ucw dot cz> 2012-05-20 11:34:27 UTC --- > > This isn't necessary. If __int128 is put on stack by caller, > > the stack must be aligned at 16 bytes. > > Not when you call function with -fpreferred-stack-boundary=3 > and it is itself compiled with -fpreferred-stack-boudnary=4 > and calls another functions passing __int128. > Thus the ABI incompatibility. ... and the alignment code is there not to align stack frame, but to align the __int128bit position within the argument area. The va_arg calls beforehand are of unknon count. > Honza
