Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84 SMI; site sun.uucp Path: utzoo!linus!decvax!decwrl!sun!guy From: guy@sun.uucp (Guy Harris) Newsgroups: net.unix Subject: Re: how does adb/dbx work? Message-ID: <2611@sun.uucp> Date: Sun, 11-Aug-85 17:21:09 EDT Article-I.D.: sun.2611 Posted: Sun Aug 11 17:21:09 1985 Date-Received: Wed, 14-Aug-85 00:35:25 EDT References: <410@uvm-cs.UUCP> <456@ittvax.ATC.ITT.UUCP> Organization: Sun Microsystems, Inc. Lines: 17 > > 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. Depends on what you mean by "hardware single step" and "out of the question". The PDP-11, VAX, M68000, and several other processors have a "trace bit" in the processor status {word|longword} which causes the processor to trap at the end of the current instruction. This is perfectly usable in a multi-user system, considering the UNIX debuggers use it. Running a program by single-stepping it is, however, slow as molasses in January, whether single-user or multi-user (consider how many instructions are executed by the kernel and the debugger per instruction executed by the debuggee). Guy Harris