Re: issue with dom0_pvh on Xen 4.20

[Manuel Bouyer <bouyer@antioche.eu.org>]

On Tue, Sep 02, 2025 at 02:28:27PM +0200, Juergen Gross wrote:
> > What puzzles me is that:
> > 
> > - %cr2 is 0, so probably the first fault wasn't a page fault
> > - RIP is %ebx + 8, so maybe the code was just clobbered by the loop?
> > 
> > Could it be the code has been moved to this location, or is about to
> > be moved away afterwards?
> 
> And indeed: from the full boot log I can see:
> 
> (XEN)     virt_base        = 0x0
> (XEN)     elf_paddr_offset = 0x0
> (XEN)     virt_offset      = 0x0
> (XEN)     virt_kstart      = 0x200000
> (XEN)     virt_kend        = 0x17bab90
> (XEN)     virt_entry       = 0x20e4d0
> 
> So virt_kentry is very near to the RIP.

thanks to this, I think I found the issue:
with Xen 4.18, the kernel is started with ebx=17bb018; with 4.20 it's
100018.

The bootstrap code assumes that the kernel is after the kernel, and the
kernel symbol table. That seems to be no longer true with Xen 4.20 and a
PVH dom0 (but probably still true in all other cases).

I can deal with that, but with the new layout how do I get the end of the
symbol table ?

-- 
Manuel Bouyer <bouyer@antioche.eu.org>
     NetBSD: 26 ans d'experience feront toujours la difference
--