see - Lions' Commentary on UNIX 6th Edition, with Source Code [1] [1] https://en.wikipedia.org/wiki/Lions%27_Commentary_on_UNIX_6th_Edition,_with_Source_Code#.

see - Lions' Commentary on UNIX 6th Edition, with Source Code [1] [1] https://en.wikipedia.org/wiki/Lions%27_Commentary_on_UNIX_6th_Edition,_with_Source_Code#.22You_are_not_expected_to_understand_this.22 https://en.wikipedia.org/wiki/Lions%27_Commentary_on_UNIX_6t... /* * If the new process paused because it was * swapped out, set the stack level to the last call * to savu(u_ssav). This means that the return * which is executed immediately after the call to aretu * actually returns from the last routine which did * the savu. * * You are not expected to understand this. */ if(rp->p_flag&SSWAP) { rp->p_flag =& ~SSWAP; aretu(u.u_ssav); }