Re: [Xen-devel] strange behavior with Multiboot2 on EFI

[Kristaps Čivkulis <kristaps.civkulis@xxxxxxxxx>]

Roger provided Xen kernel binary for me and it worked. I don't know
why I couldn't build it properly on FreeBSD.

>> menuentry 'Xen kernel' {
>>         set root='(hd0,1)'
>>         multiboot2 /xen
>
> I think that you should add at least this to Xen command line:
>   dom0_mem=1g,max:1g guest_loglvl=all loglvl=all sync_console com1=115200,8n1 
> console=com1,vga
>
> And what about dom0 kernel? module2?

At first I tried to load Xen kernel only.
Is 'module2' the same as 'module' but only for multiboot2? There isn't
information on GRUB manual [0].
Also, how should dom0 be provided to Xen? Is passing it as multiboot2
module enough for Xen kernel to understand?

>> sudo qemu-system-x86_64 \
>>        -hda linux.img \
>>        -bios OVMF-pure-efi.fd \
>>        -m 4096 \
>>        -debugcon file:debug.log -global isa-debugcon.iobase=0x402
>
> You are missing at least serial console and GDB setup. I would suggest
> that you add to the QEMU command line at least this:
>   -serial telnet::10232,server,nowait -gdb tcp::10234

I was using QEMU built in serial console (View -> serial0) and by
default I can connect to QEMU with gdb by command "target remote
localhost:1234".

> Hence, you are able to get load offset using link_base_addr and 
> load_base_addr.
> Then add load offset to the multiboot2 UEFI entry point. After that set 
> breakpoint
> using "hb" in GDB (hardware assisted breakpoint). Do not use "b". IIRC it is
> software breakpoint (int 3) and it will not work here because the int 3 opcode
> is overwritten by the GRUB2 during final Xen code relocation. In general I 
> suggest
> you to use "hb". It is more reliable.

Thanks!


On my FreeBSD multiboot2 loader implementation Xen kernel produces
following output:

 Xen 4.11-rc
(XEN) Xen version 4.11-rc (root@xenrtcloud) (gcc (Debian 4.9.2-10)
4.9.2) debug=y  Fri Jun 22 09:29:19 UTC 2018
(XEN) Latest ChangeSet:
(XEN) Bootloader: unknown
(XEN) Command line: dom0_max_vcpus=4 dom0pvh=1 console=com1,vga
com1=115200,8n1 guest_loglvl=all loglvl=all
(XEN) Xen image load base address: 0
(XEN) Video information:
(XEN)  VGA is graphics mode 2048x2048, 32 bpp
(XEN) Disc information:
(XEN)  Found 0 MBR signatures
(XEN)  Found 1 EDD information structures
(XEN)
(XEN) ****************************************
(XEN) Panic on CPU 0:
(XEN) dom0 kernel not specified. Check bootloader configuration.
(XEN) ****************************************
(XEN)
(XEN) Reboot in five seconds...

The problem is with line
(XEN) Xen image load base address: 0
Which is not true, because I loaded it into 0x200000. I also provide
image load base physical address tag with the same value. Is there
something else I should set to provide Xen with correct load base
address?

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