Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!romp!auschs!d75!awdprime!stingray!marc
From: marc@stingray..austin.ibm.com (Marc J. Stephenson/140000;1C-22)
Newsgroups: comp.unix.questions
Subject: Re: Debugger watchpoints in UNIX ?
Keywords: debug watchpoint
Message-ID: <1749@awdprime.UUCP>
Date: 8 Mar 90 17:41:27 GMT
References: <22567@pasteur.Berkeley.EDU>
Sender: news@awdprime.UUCP
Reply-To: marc@awdprime.austin.ibm.com.UUCP (Marc J. Stephenson/140000)
Organization: IBM AWD, Austin, TX
Lines: 21

In article <22567@pasteur.Berkeley.EDU> luciano@canuck.Berkeley.EDU (Luciano Lavagno) writes:
>
> 
>Has anybody heard of an efficient implementation of watchpoints, i.e. 
>breakpoints activated whenever an arbitrary position in memory (e.g. a 
>field of a dynamically allocated structure) changes value ?
>Both dbx and saber can do something similar, but with horrendous 
>performance penalty ("stop address" commands).

If a debugger has to perform this operation in software, then it will
be extremely slow; if it has hardware assist, then it can be done reasonably
quickly.  If you are stuck doing with a software implementation, then you
will be better off if you can narrow down the scope of the operation (trace
expr at line, trace addr in procedure, etc...) to reduce the cost.  If it's
not possible to narrow the scope of the watch, then start it off and go get 
something to eat.

Marc Stephenson (marc@stingray.austin.ibm.com)
DISCLAIMER: The content of this posting is independent of official IBM position.
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