19acc770c2
sigreturn() ABI and the signal context on the stack. Make the trapframe (and its shadows in the ucontext and sigframe etc) 8 bytes larger in order to preserve 16 byte stack alignment for the following C code calls. I could have done some padding after the trapframe was saved, but some of the C code still expects an argument of 'struct trapframe'. Anyway, this gives me a spare field that can be used to store things like 'partial trapframe' status or something else in the future. The runtime impact is fairly small, *except* for threaded apps and things that decode contexts and the signal stack (eg: cvsup binary). Signal delivery isn't too badly affected because the kernel generates the sigframe that sigreturn uses after the handler has been called. The size of mcontext_t and struct sigframe hasn't changed. Only the last few fields (sc_eip etc) got moved a little and I eliminated a spare field. mc_len/sc_len did change location though so the sanity checks there will still trap it.