Cristiano Di Buduo wrote: > Sorry, of course I meant WindowProc. I am guessing that what's happening here is that since you are in a callback from the operating system, the calling frame has violated gcc's assumption that %esp will always be aligned to 16 at function entry. gcc aligns %esp once at program startup and then ensures that it stays aligned at each function call, so that prologues of functions that have aligned data don't have to contain code to align it every time. But if the calling frame doesn't maintain this convention then it all falls apart. You can use __attribute__((force_align_arg_pointer)) on the function to tell gcc not to assume that the incoming %esp is 16 byte aligned and to instead insert the slower explicit alignment code in the prologue. However, this attribute wasn't added until gcc 4.2 so if you're using the Cygwin system compiler (currently based on 3.4) it won't work. Brian
