[TUHS] SDB debugger

Rob Pike robpike at gmail.com
Sat May 2 11:22:25 AEST 2020

I don't remember dbx appearing in our lab, but that doesn't mean it wasn't

I did quite a bit of work on adb, renamed db, mostly finishing things up
and fixing a lot of bugs, to make it actually work in Plan 9. I had several
conversations with Steve Bourne about it to understand why it seemed
broken, and how to fix it. Once fixed, It could do some remarkable stuff
but nobody but me seemed to care because it was lower level than
cdb/sdb/gdb. I liked it because, once those bugs were fixed, it got the
right answer, something gdb never did back then. The [scg]db of yesteryear
was far too unreliable and crashy for me. After it  dumped core for the nth
time on top of the core I was debugging, I gave up on it. But I was never a
debugger-first programmer. None of us in the lab were, and that's probably
why the debugging setup in Unix is to this day so weak compared to what
other systems provide.

The sdb/gdb line also had a peculiar property of not answering the question
you were asking, although I don't remember the details. It was more
interested in the symbols than the code, and that could get in the way. The
failure of the compiler to give good symbols didn't help. And now we have
DWARF, for which my only comment is: oof, the sound one makes catching a
dropped bag of concrete mix.

One debugger that we used a lot, although more as a scripting language for
things like tracing system calls and checking for malloc leaks than as an
interactive tool, was Phil Winterbottom's Acid. It has a crazy language but
once you licked it (I think the only three who did were Phil, me, and Russ
Cox) it was very powerful. Acme had some front-end code for it that made it
great for displaying multithreaded program stacks.

Pi was cool, but that was earlier and tied to the Jerq/Blit and C++.


On Sat, May 2, 2020 at 10:50 AM Noel Hunt <noel.hunt at gmail.com> wrote:

> When it comes to Eight Edition, please don't forget Tom Cargill's
> 'pi'. There was also a version I believe that was used as the
> debugger for programs on the Blit/Jerq; it seems to be known as
> '4pi' in the source.
> On Sat, May 2, 2020 at 6:49 AM Paul Ruizendaal <pnr at planet.nl> wrote:
>> Reading some more stuff about the road from 7th Edition to 8th Edition,
>> this time about debuggers.
>> My current understanding is as follows:
>> - On 6th edition the debugger was ‘cdb’
>> - On 7th edition it was ‘adb’, a rewrite / evolution from ‘cdb’
>> - In 32V a new debugger appears, ‘sdb’. Its code seems a derivative from
>> ‘adb’, but the command language is substantially reworked and it uses a
>> modified variant of the a.out linker format - in essence the beginnings of
>> ‘stabs’. Of course the compiler, assembler, linker and related tools all
>> emit/recognize these new symbol table elements.
>> - The July 78 file note by London/Reiser does not mention a reworked
>> debugger at all; the 32V tape that is on TUHS has ’sdb' files that are
>> dated Feb/Mar 1979. This stuff must have been developed between July 78 and
>> March 79.
>> - In the SysIII and 3BSD code on TUHS (from early 80 and late 79
>> respectively) the stabs format is more developed. For SysIII it is ‘VAX
>> only’. With these roots, it is not surprising that it is also in 8th
>> Edition.
>> Two questions:
>> (1) According to Wikipedia the original author of the stabs format is
>> unknown. It also says that the original author of ‘sdb’ is unknown. Is that
>> correct, is the author really unknown?
>> (2) As far as I can tell, the ’sdb’ debugger was never back ported to 16
>> bit Unix, not in the SysIII line and not in the 2.xBSD line. It would seem
>> to me that the simple stabs format of 32V would have lent itself to being
>> back ported. Is it correct that no PDP11 Unix used (a simple) stabs tool
>> chain and debugger?
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