Re: debuggers (Willem Jan Withagen)
Thu, 11 Nov 1993 11:43:54 GMT

          From comp.compilers

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Newsgroups: comp.compilers
From: (Willem Jan Withagen)
Keywords: debug
Organization: Digital Information Systems Group, Eindhoven University of Technology
References: 93-10-124 93-11-062
Date: Thu, 11 Nov 1993 11:43:54 GMT

[I modified gdb 3.x a few years ago to add watchpoints, implemented using
the 386's hardware watchpoints. It worked reasonably well, but the gdb
maintainers declined to take my code back because they wanted something that
would work everywhere. I believe that they think that with some cooperation
from the paging system they can provide useful watchpoints via page
faults. -John]

The Z80 hobby system I build in early 80's contained a special hardware
card that could be used to specify address and some kind of data relation
with masks, AND's and OR's, and when one of the expressions triggered, it
interupted the processor. It was used in a tiny debugger I wrote. But it
was really efficient. Much more efficient than running every instruction
seperately, the card could also single step. And in reduced the codesize
of the debugger significantly, because application ,debugger and CPM all
had to fit in 96K. (Yes that's > 64K, but then the lower 32K could be
swapped. :-) )

In a German magazine, they had an article where the same type of hardware
was used to given 8086 systems the same kind of functionality. It then
interfaced with the Turbo Debugger. Looked like a real nice solution.

I would not mind if the hardware watchpoint stuff was available as a
seperate patch, which people could apply if they want.

Willem Jan
Digital Information Systems Group, Tel: +31-40-473401, Fax: +31-40-448375
Room EH 10.35 Eindhoven University of Technology
P.O. 513, 5600 MB Eindhoven, The Netherlands

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