Messages in this thread | | | Date | Mon, 30 Jun 2008 14:52:10 -0700 | From | Jeremy Fitzhardinge <> | Subject | Re: Regression: boot failure on AMD Elan TS-5500 |
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Sean Young wrote: > 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.
It's a bit odd that the boot loader neglected to set up ds properly, but changing the testb line to
testb $(1<<6), %cs:BP_loadflags(%esi)
should work. (Or perhaps a %ss: override would be better?)
I'm assuming that the GDT setup isn't completely mad and that the segments have the same base at least.
J
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