Queue - July/August 2008

understand Solaris; and Steve, you developed adb because it was a technology that you needed to understand your programs.

SB Exactly. It’s rather similar to Eric’s experience in that the debuggers that existed at the time interpreted the information a little more than I was comfortable with. That was why I wrote adb—ju st so I knew that what I saw was what I got.

BC Can you elaborate on that?

SB First of all, I couldn’t find the answers to my questions, because only a limited window of information was coming out of the debugger at the time. DB was the early debugger in Unix, and that was fairly simple but had a bunch of things missing. Also, we were moving to the separate I&D space on the PDP, so there were changes in the system environment that needed to be reflected in the debugger, and capabilities in the a.out files that were being changed that weren’t being reflected in the debugger.

It wasn’t so much that the debugger was broken when it was written; it’s that it wasn’t keeping track of the changes in the system environment that we were debugging.

BC Sounds like bit rot.

SB Yes, it was bit rot. Actually, at the time, I had written an Algol 68 compiler that I was porting to the PDP- 11 and I wanted to have stuff in there to interpret the Algol 68 stack trace.

BC This is the famous “$a”?

SB This is the $a, exactly.

BC I discovered $a when I attempted to write $q while using adb at Sun in 1996. I typed $a by accident and Steve Bourne, like an apparition from the past, whispered to me, “No Algol 68 here,” which is the message you get out of adb when you type $a.

I was flabbergasted! Suddenly, the deepest heart of the system was speaking directly to me. No Algol 68 here? There hadn’t been Algol 68 in Solaris ever, and so needless to say, $a has become something of legend. I believe Steve knows, but I’ll let folks discover it for themselves,

in mdb we have implemented $a. In adb compatibility mode it gives you the message, “No Algol 68 here.” Mdb gives you its own smarmy message on $a.

One more question: What was the moment when you knew that the investment in the tools you developed paid off?

EA Probably almost instantly. Syslog was one of those
things where it was just so obvious from the start that it
was going to be valuable. It wasn’t something where you
go, “Well, I’ll just build this little tool,” and then three
months later you say, “Oh, wow, I’m glad I wrote that
tool.” I was trying to debug
things that were basically
undebuggable.

BRYAN

SB I don’t remember a particular event, but I knew fairly early on that you couldn’t use the other debuggers to do what we were doing, so it was almost like there wasn’t another choice at the time. It wasn’t until many years later that an ACM Fellow, whose name I’ll omit, said, “Adb is really cool. It just does what it does, and that’s it.”

EA I have another example, which is slightly different. I wrote a front end for the SCCS (source code control system) at Berkeley. I had written a source management system while

I was in high school that did tape-to-tape stuff on the IBM 1401, so I was actually an early adopter of that sort of stuff. Back then people weren’t keeping change sets. You couldn’t do deltas, you couldn’t see your history. So I wrote this front end primarily for myself, but I was able to convince Bill Joy et al. that they should use it on Berkeley Unix. When we finally got to the point where we were saying, “OK, everything in the system is actually going to be under source management,” that was a real “Finally... and I had something to do with that” kind of moment. Q