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From: dyson@cbnewsk.att.com (john.s.dyson)
Newsgroups: comp.unix.questions
Subject: Re: why different swapping modes on executables?
Summary: I think that 410, 413, etc were branch instructions
Message-ID: <1991Mar14.043302.3567@cbnewsk.att.com>
Date: 14 Mar 91 04:33:02 GMT
References: <1991Mar12.012401.557@nowhere.uucp> <573@adpplz.UUCP>
Distribution: na
Organization: AT&T Bell Laboratories
Lines: 29

In article <573@adpplz.UUCP>, martin@adpplz.UUCP (Martin Golding) writes:
> In <1991Mar12.104352.23097@kithrup.COM> sef@kithrup.COM (Sean Eric Fagan) writes:
> 
> >In article <1991Mar12.012401.557@nowhere.uucp> sking@nowhere.uucp (Steven King) writes:
> >>    While I think I understand what the difference is, I don't understand
> >> why the difference. Is there any advantage to one over the other? How
> >> does one, short of directly editing the binary, assign one or the other?
> >> ( the link editor doesn't offer any clues ) 
> 
> >At one point, the linker would just willy-nilly put things back to back.
> >For example, text might end at 0x1231, and data would then begin at 0x1232.
> >When paging, you do *not* want to use old data.  Therefore, if you want to
> >page directly from disk, you arrange things such that everything is in a
> >decent arrangement (which is what your kernel would do for you when it
> >swapped pages to the swap device).
> 
> My impression is that the (original) version of the Magic Number was
> the actual value to load into the PDP 11 MMU control register, to select
> one or the other model.
> 
> Martin Golding    | sync, sync, sync, sank ... sunk:
> Dod #0236         |  He who steals my code steals trash.
> {mcspdx,pdxgate}!adpplz!martin or martin@adpplz.uucp

My memory is sometimes foggy, but I think that the magic number was
the branch instruction around some header info in the a.out??????

John Dyson
inuxy.att.com