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Re: IP32 prom crashes due to __pa() funkiness

To: Linux MIPS List <linux-mips@linux-mips.org>
Subject: Re: IP32 prom crashes due to __pa() funkiness
From: Kumba <kumba@gentoo.org>
Date: Sat, 17 Mar 2007 15:52:16 -0400
In-reply-to: <cda58cb80703010139y3e5bbb8eqa4d25b75ba658a22@mail.gmail.com>
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(whoops, reply didn't send to the ML, sorry Frank!)


Franck Bui-Huu wrote:
> Hi,
>
[snip]
>
> Well, it means that you previously used CONFIG_BUILD_ELF64=y (this
> implied that PAGE_OFFSET is in XKPHYS) whereas your kernel has CKSEG
> load address (symbols need PAGE_OFFSET in CKSEG for address
> translation).
>
> So the question is why can't you use CONFIG_BUILD_ELF64=n (and
> reagarding the current definition of CONFIG_BUILD_ELF64).
>
[snip]
>
> It makes me think that I posted a patch for that a couple of weeks ago:
>
> http://marc.theaimsgroup.com/?l=linux-mips&m=117154480225936&w=2
> http://marc.theaimsgroup.com/?l=linux-mips&m=117154480126802&w=2
> http://marc.theaimsgroup.com/?l=linux-mips&m=117154587014827&w=2
>
> Basically this patch removes CONFIG_BUILD_ELF64 and makes Kbuild to use
> '-msym32' switch if you really need it. Kbuild makes its choice according
> the load address of your kernel image.
>
> Could you give it a try ? This patch was based on 2.6.20 but it should
> apply fine on a 2.6.21-rc[12].

Tested, and it still failed.

And I didn't always use CONFIG_BUILD_ELF64. In fact, for the longest time (up until 2.6.17) I built IP32 and 64bit IP22 kernels without CONFIG_BUILD_eLF64, passing -mabi=o64 (a.k.a., the binutils hack). This let me use the plain 'vmlinux' target w/o the need for an objcopy to boot these systems. After 2.6.17, the nature of o64 was mostly neutered, so I switched to using CONFIG_BUILD_ELF64 and the 'vmlinux.32' target, as this is apparently the way Debian builds their IP32 kernels (and was the way geoman/spbecker said I should've been using all along).

So with the changes brought in by __pa(), I suppose a new, RightWay(TM) to build IP32 (and conversely, 64bit IP22) kernels needs to be found. These two systems are particularly wacky, hence why they need a bit more special care than more traditional, proper, 64bit systems like Origin and Octane.

Also, Peter raises a good point in this case. It sounds like a re-thinking of how all this address stuff is handled will fix not only special cases like IP32/IP22, but the really weird systems, like IP28, as well. Which would be a big plus in my opinion.


--Kumba

--
Gentoo/MIPS Team Lead

"Such is oft the course of deeds that move the wheels of the world: small hands do them because they must, while the eyes of the great are elsewhere." --Elrond


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