mach_cpucontext_xfree
mach_cpucontext_xfree(cp, arg, err, MACH_CPUCONTEXT_OP_START);
mach_cpucontext_xfree(cp, ctx, 0, MACH_CPUCONTEXT_OP_STOP);
mach_cpucontext_xfree(cp, ctx, rv, MACH_CPUCONTEXT_OP_STOP);
extern void mach_cpucontext_xfree(struct cpu *, void *, int, int);