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Date: Fri, 20 May 2005 14:12:00 -0000
From: "Eli Zaretskii" <eliz@gnu.org>
To: Johan Rydberg <jrydberg@virtutech.com>
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CC: dan@shearer.org, gdb@sources.redhat.com
In-reply-to: <428DD67E.2030507@virtutech.com> (message from Johan Rydberg on
	Fri, 20 May 2005 14:22:22 +0200)
Subject: Re: [discuss] Support for reverse-execution
Reply-to: Eli Zaretskii <eliz@gnu.org>
References: <20050519012254.GZ19642@erizo.shearer.org> <428C8E04.3000305@virtutech.com> <01c55d27$Blat.v2.4$69471120@zahav.net.il> <428DD67E.2030507@virtutech.com>
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> Date: Fri, 20 May 2005 14:22:22 +0200
> From: Johan Rydberg <jrydberg@virtutech.com>
> Cc: dan@shearer.org, gdb@sources.redhat.com
> 
> (1)  foo (i);
>       0:   80 7f 00 08     lwz     r3,8(r31)
>       4:   48 00 00 01     bl      X <foo>
>       8:                   nop
> (2)  i = 0;
>       c:   38 00 00 00     li      r0,0
>      10:   90 1f 00 08     stw     r0,8(r31)
> 
> <foo>:
>      ....
>      4c:   4e 80 00 20     blr
> 
> You start with PC = c, and single steps backwards.  You end up on
> the nop-insn.  This is inside the single step range of line 1. So
> you single step another instruction backwards, and suddenly you
> stop at PC = 4c

I guess I don't understand how backwards movement works, because I
thought stepping backwards over the branch instruction does _not_ take
the branch, but rather rewinds the machine state to what it was before
the branch instruction.

Anyway, thanks for the explanations.

> >>+   add_com_alias ("rn", "rnext", class_run, 1);
> > 
> > Do we want another alias called "previous"?
> 
> I think so, and maybe also "prev" and/or "pre".

The additional aliases won't be necessary, since they both are
unambiguous abbreviations of "previous".  So they will work even if we
don't define them as aliases.