Date: Fri, 30 Aug 2002 17:36:36 -0700 From: Peter Wemm <peter@wemm.org> To: John Baldwin <jhb@FreeBSD.org> Cc: cvs-all@FreeBSD.org, cvs-committers@FreeBSD.org Subject: Re: cvs commit: src/sys/boot/i386/loader Makefile Message-ID: <20020831003636.90ED52A7D6@canning.wemm.org> In-Reply-To: <XFMail.20020830111122.jhb@FreeBSD.org>
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John Baldwin wrote:
>
> On 30-Aug-2002 John Baldwin wrote:
> > jhb 2002/08/30 07:59:47 PDT
> >
> > Modified files:
> > sys/boot/i386/loader Makefile
> > Log:
> > Revert previous untested revision. The i386 loader consists of three par
ts:
> > At the front is btxldr, in the middle is BTX itself (our mini-kernel), an
d
> > then the 'client' (loader.bin) which is the actual loader itself. boot2
> > just executes a raw ELF or a.out binary with the only setup provided bein
g
> > that a bootinfo structure is passed on the stack. Now, since loader.bin
> > is a BTX client, the loader needs to be able to locate a BTX kernel for
> > the client to execute in the context. Thus, just like pxelder, btxldr
> > uses the a.out header on the loader binary to find the BTX kernel stored
> > in the loader and set it up. It does _not_ just reuse the BTX kernel
> > that boot2 invoked it with. This is because it can't assume that it will
> > _have_ a "spare" BTX kernel lying around. For example, when cdboot
> > loads the loader there isn't an existing BTX kernel. In fact, cdboot
> > will only work with an a.out loader as well since it also "borrows" the
> > BTX kernel in the loader binary (which it finds by parsing the a.out
> > header) just as pxeldr does. The only difference between cdboot and
> > pxeldr is where they get /boot/loader from.
> >
> > If we wanted to make /boot/loader be an actual ELF binary we would need
> > to change the following utilites to handle that (and they all have to be
> > able to handle locating the BTX kernel inside of an ELF binary somehow):
> > - btxldr
> > - pxeldr
> > - cdboot
> >
> > If we didn't want to require a flag day but make the transition smooth
> > then we need to be able to support both a.out and ELF versions of
> > /boot/loader which isn't exactly trivial since all three of these utiliti
es
> > are written in assembly.
> >
> > Pointy-hat to: peter
>
> Hmm, in hindsight this message is perhaps a bit harsh. Sorry, Peter. I
> don't see how you could have succesfully tested it though, the loader just
> won't work in any case if /boot/loader isn't a.out atm.
If it is any consolation, I had to recover my laptop with a hosed /boot/loader
and /boot/loader.old today. :-]
Cheers,
-Peter
--
Peter Wemm - peter@wemm.org; peter@FreeBSD.org; peter@yahoo-inc.com
"All of this is for nothing if we don't go to the stars" - JMS/B5
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