Article 4998 of alt.sys.pdp10: Path: news3.best.com!nntp1.ba.best.com!not-for-mail From: inwap@best.com (Joe Smith) Newsgroups: alt.folklore.computers,alt.sys.pdp10 Subject: Re: How in Hell did the Great Unix to NT Migration begin?? Date: 4 May 1999 05:18:25 -0700 Organization: Chez Inwap Message-ID: <7gmoih$mgg$1@shell3.ba.best.com> References: <371be3e4.0@newsfeed.one.net> <7g9jj5$88h$2@antiochus.ultra.net> <37324689.4539727@news.kivex.com> <7gmjv5$aq5$1@antiochus.ultra.net> Lines: 50 NNTP-Posting-Host: shell3.ba.best.com X-Trace: nntp1.ba.best.com 925820308 226 inwap@206.184.139.134 Xref: news3.best.com alt.folklore.computers:129493 alt.sys.pdp10:4998 In article <7gmjv5$aq5$1@antiochus.ultra.net>, wrote: >In article <37324689.4539727@news.kivex.com>, > nospam-gagner@clark.net (Philip Gagner) wrote: >>Yes, this was the theory. In practice, if what one was debugging >>wasn't really VERY likely to halt the system, then you a user with >>appropriate privileges could load FILDDT and watch (as well as modify) >>memory directly, including monitor tables, etc. > >Nitpik here. FILDDT was the program to patch the monitor file >that was one disk...not the code currently running--that's what >EDDT was for and could be invoked by that nefarious command >. Or am I misremembering? Incomplete memory. FILDDT could peek at the running monitor. If write-enabled, FILDDT could poke at the running monitor. You could not set breakpoints with FILDDT, but you could load the symbol table from SYSTEM.EXE and view locations and values symbolically. I would use EDDT to set a breakpoint on a dummy routine when the Monitor was loaded. While the system was running, I would use FILDDT to patch some instruction to jump to the dummy routine under certain conditions. When the system hit that condition, the Monitor would come to a screeching halt, with EDDT running on the console. >I should probaby point out that DDT.EXE, FILDDT.EXE and EDDT.REL >were all built from the same DDT.MAC source file with the >appropriate feature test switches. Don't forget DDT.REL (statically loaded with user's program), VMDDT.EXE (dynamically merged in when DDT.REL was not loaded), and that FILDDT came in two flavors (TOPS-10 and TOPS-20) all from the same source. EDDT.REL, while designed to run in kernel mode, was capable of running in user mode as well, using UUOs or JSYS for I/O to the terminal. This allowed for patching the Monitor by using .GET SYS:SYSTEM .DDT * manually patch things or read in a file with DDT commands ^C .SAVE SYS:SYSTEM -Joe -- INWAP.COM is Joe Smith, Sally Smith and our cat Murdock. (The O'Hallorans and their cats moved to http://www.tyedye.org/ Nov-98.) See http://www.inwap.com/ for PDP-10, "ReBoot", "Shadow Raiders"/"War Planets"