From: "Eli Zaretskii" <eliz@is.elta.co.il>
To: drow@mvista.com
Cc: ac131313@ges.redhat.com, gdb-patches@sources.redhat.com
Subject: Re: [rfc] 16 bit real-mode for the i386
Date: Fri, 30 Aug 2002 12:31:00 -0000 [thread overview]
Message-ID: <2950-Fri30Aug2002221152+0300-eliz@is.elta.co.il> (raw)
In-Reply-To: <20020829213653.GA24048@nevyn.them.org> (message from Daniel Jacobowitz on Thu, 29 Aug 2002 17:36:53 -0400)
> Date: Thu, 29 Aug 2002 17:36:53 -0400
> From: Daniel Jacobowitz <drow@mvista.com>
>
> > +static void
> > +i386_write_pc (CORE_ADDR pc, ptid_t ptid)
> > +{
> > + if (i386_real_mode_p)
> > + {
> > + CORE_ADDR cs = read_register_pid (CS_REGNUM, ptid);
> > + pc = pc - (cs << 4);
> > + }
> > + write_register_pid (PC_REGNUM, pc, ptid);
> > +}
> > +
>
> Left shift of _four_? Surely the PC is more than four bits.
It's true that PC can be more than 4 bits, but the code above is still
correct. That's why real mode can only access 20 bit addresses:
16+4=20.
You can look at this issue this way: for each linear 2-bit address,
there are many CS:PC combination that all point to that address.
next prev parent reply other threads:[~2002-08-30 19:10 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-08-29 13:33 Andrew Cagney
2002-08-29 14:37 ` Daniel Jacobowitz
2002-08-29 14:46 ` Andrew Cagney
2002-08-29 14:46 ` Kevin Buettner
2002-08-29 14:52 ` Daniel Jacobowitz
2002-08-30 12:31 ` Eli Zaretskii [this message]
2002-08-29 15:36 ` Mark Kettenis
2002-08-30 12:47 ` Andrew Cagney
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