_REG_UESP
u->uc_mcontext.__gregs[_REG_UESP] = (uintptr_t) sp;
gr[_REG_UESP] = (__greg_t)sp;
#define pthread__uc_sp(ucp) ((ucp)->uc_mcontext.__gregs[_REG_UESP])
gr[_REG_UESP] = tf->tf_esp;
tf->tf_esp = gr[_REG_UESP];
#define _UC_MACHINE_SP(uc) ((uc)->uc_mcontext.__gregs[_REG_UESP])