Path: utzoo!attcan!ncrcan!hcr!markm
From: markm@hcr.UUCP (Mark Mendell)
Newsgroups: comp.arch
Subject: Re: break on data reference
Message-ID: <2337@hcr.UUCP>
Date: 26 Oct 89 18:08:37 GMT
Organization: HCR Corporation, Toronto
Lines: 25

This is my turn for a pseudo-plug:

DbXtra 2.1 (HCR's port of BSD dbx) on 386/IX also uses the 386 debug registers
to tell when a variable has been changed (or accessed), and also to test
when a given condition becomes true.  I.e.  stop if i > 99

A brief (and very unbalanced test) gave me a test case where the new version
(using the debug registers) ran the test program 300 times faster than the
old method of doing this in dbx, which is to stop after every statement,
and then test the condition.  I also found that the penalty for using the
debug registers at all was about 3% slowdown.  This is because the LE bit must
be set in the debug control register, so that 'exact data breakpoint match'
is true, and the data breapoints are reported on the instruction that causes
them.  I assume that this slows down the pipeline somewhat.

Dbxtra 2.1 for 386/IX will be available in January '90.

Does anyone know when the 386 debug registers dr4 and dr5 will be available?
The 486?  586? It would be nice to be able to span more than 16 bytes
worth of data for these breakpoints!
-- 
Mark Mendell, HCR Corporation
	    130 Bloor St. W., Suite 1001, Toronto
	    Phone: (416)-922-1937, Fax:	(416)-922-8397
	    Usenet:	...!hcr!markm