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SubjectRe: Regression: boot failure on AMD Elan TS-5500
On Mon, Jun 16, 2008 at 04:19:44PM +0000, Sean Young wrote:
> On Mon, Jun 16, 2008 at 06:37:12AM -0700, Jeremy Fitzhardinge wrote:
> > Rusty Russell wrote:
> > >On Monday 16 June 2008 22:11:39 Sean Young wrote:
> > >
> > >>The symptons are either a crash or reboot on booting the kernel. No
> > >>printk's have occurred yet -- even with early printk on.
> > >>
> > >>2.6.15 worked on this board however current does not. I've bisected it to:
> > >>
> > >> commit a24e785111a32ccb7cebafd24b1b1cb474ea8e5d
> > >> Author: Rusty Russell <rusty@rustcorp.com.au>
> > >> Date: Sun Oct 21 16:41:35 2007 -0700
> > >>
> > >> i386: paravirt boot sequence
> > >>
> > >
> > >Hi Sean,
> > >
> > > Thanks for tracking this down. Can we try reverting this in pieces to
> > > see exactly what the cause was?
> > >
> > >1) Revert arch/x86/boot/compressed/head_32.S
> > >2) If that doesn't fix it, Try removing the 8 lines which were added to
> > >arch/x86/kernel/head_32.S
> > >
> > And the arch/x86/boot/compressed/misc_32.c change too, just in case...
>
> Reverting only head_32.S makes the problem go away. I didn't try any other
> changes.

Looking at the beginning of startup_32, it seems ds is used before it is set:

startup_32:
cld
/* test KEEP_SEGMENTS flag to see if the bootloader is asking
* us to not reload segments */
testb $(1<<6), BP_loadflags(%esi)
jnz 1f

cli
movl $(__BOOT_DS),%eax
movl %eax,%ds
movl %eax,%es
movl %eax,%fs
movl %eax,%gs
movl %eax,%ss
1:

Since the testb instruction is a dereference, ds is implicitly used. If
I move the testb to after "movl %eax,%ds" it seems to work (not that it
would make any sense there, but just to prove the point).

1) Am I barking up the wrong tree?

2) If I'm right I have no idea what the correct solution is; it seems that
a chicken & egg issue is introduced.

Please advise. I am very new to all of this.


Sean


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