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From: marc@stingray.austin.ibm.com (Marc J. Stephenson/140000;1C-22)
Newsgroups: comp.unix.aix
Subject: Re: PT_STEP parameter to ptrace() on RS/6000
Summary: Sorry, no PT_STEP
Message-ID: <6595@awdprime.UUCP>
Date: 11 Apr 91 18:15:31 GMT
References: <40922@netnews.upenn.edu>
Sender: news@awdprime.UUCP
Organization: IBM AWD, Austin
Lines: 14

PT_STEP is not supported in the AIX 3.1 kernel.  dbx and adb do not use
PT_STEP to perform single-stepping; it is done via inserting trap instructions
in the debuggee process (then replacing the original instruction).  FYI, dbx
use a tgte r2,r2 (trap if register 2 is greater than or equal to register 2,
a normally nonsensical instruction) for its traps.

The hardware does not support single-stepping, so it was decided to leave the
software trapping code at the application level rather than in ptrace(), where
all the same software trapping would have to take place.  

-- 
Marc Stephenson		      IBM PSPA (Personal System Programming - Austin,TX)
DISCLAIMER: The content of this posting is independent of official IBM position.
marc@stingray.austin.ibm.com 	VNET: MARC at AUSVMQ  	IBM T/L: 793-3796