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Re: issue with dom0_pvh on Xen 4.20
- To: Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Tue, 2 Sep 2025 15:55:14 +0200
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- Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>
- Delivery-date: Tue, 02 Sep 2025 13:55:27 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 02.09.2025 15:41, Manuel Bouyer wrote:
> 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
DYM "start info is after the kernel" or some such, seeing that that's what
%ebx is about?
> 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 ?
You'll need to handle that internally, I expect, perhaps from properties of
your (ELF) binary.
Jan
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