how does adb/dbx work?

[Randy D. Smith]

In article <410 at uvm-cs.UUCP> hartley at uvm-cs.UUCP (Stephen J. Hartley) writes:
>I was wondering if somebody could explain how adb (and dbx) executes programs.
>Does it have a software simulator that interprets the instructions in the
>object file of the program being debugged?  Or does it use the VAX hardware
>to execute the program, say by hardware single-stepping?...

dbx uses software simulation.  I recall finding code to use the hardware-
trace-bit method, but it was never called from anywhere.  Instead, dbx
would determine where the next location would be based on the current
machine state and the next instruction to be executed.  I think some of
the stuff was taken from adb verbatim, by the way, so I expect it behaves
similarly.  It sure made my day when I found the trace bit wasn't being
used (the machine I ported it to had no trace bit).
-- 
				Randy D. Smith	(919) 248-6136
			   Data General, Research Triangle Park, NC
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