Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/17/84; site ittvax.ATC.ITT.UUCP Path: utzoo!linus!philabs!cmcl2!seismo!harvard!talcott!panda!genrad!decvax!ittatc!ittvax!goldman From: goldman@ittvax.ATC.ITT.UUCP (Ken Goldman) Newsgroups: net.unix Subject: Re: how does adb/dbx work? Message-ID: <456@ittvax.ATC.ITT.UUCP> Date: Fri, 9-Aug-85 12:24:01 EDT Article-I.D.: ittvax.456 Posted: Fri Aug 9 12:24:01 1985 Date-Received: Mon, 12-Aug-85 22:33:47 EDT References: <410@uvm-cs.UUCP> Organization: ITT-ATC, Shelton Ct. Lines: 14 > I was wondering if somebody could explain how adb (and dbx) executes programs. > Does it have a software simulator that interprets the instructions in the > object file of the program being debugged? Or does it use the VAX hardware > to execute the program, say by hardware single-stepping. Maybe I can help with some PDP11 insight. First, hardware single step is out of the question in a multi-user system. The way the PDP11 debuggers work is by replacing the instruction to be traced with a trap instruction. Then the software runs full speed until it hits the trap, at which point you enter the debug software. At that point you can examine registers, memory, etc. The debugger I used was for assembly language. I suppose that a symbolic debugger understands the symbol tables and such.