LP_SINGLESTEP
ISSET(lt2->l_pflag, LP_SINGLESTEP));
ISSET(lt->l_pflag, LP_SINGLESTEP) || req == PT_STEP);
CLR(lt2->l_pflag, LP_SINGLESTEP);
CLR(lt->l_pflag, LP_SINGLESTEP);
SET(lt->l_pflag, LP_SINGLESTEP);
CLR(lt->l_pflag, LP_SINGLESTEP);