CompuServe Messages

68000 and 8086 stack frames are pretty much the same – the registers used obviously differ, but that's about it. When a function is called, arguments are pushed in the reverse order (so that the first argument is pointed to by the stack pointer). The function is then called, which means the return address is now where the stack pointer points to. Within the function, automatic variables are then allocated on the stack. This is done with the link instruction on the 68K. At this point, the frame register (a5 on the 68K) is setup so that a5+4 points to the 1st argument to the function, and negative offsets from a5 point to local variables. There's no portable way to figure out the contents of the stack frame register in C – however, taking the address of the top-most local variable can usually give you an indication. From within a debugger, simply look at the A5 register. -Mike