Re: bimodal PAE and compatibility

[Gerd Hoffmann <kraxel@suse.de>]

John Levon wrote:
> On Mon, Jan 08, 2007 at 04:05:36PM +0100, Gerd Hoffmann wrote:
> 
>>> We currently ship a PAE 32-bit domU that we can trivially make bimodal,
>>> except that if we set it to "bimodal", then older Xens will default to
>>> thinking the domU is not PAE:
>>>
>>> 353     dsi->pae_kernel = PAEKERN_no;
>>> 354     if ( dsi->__elfnote_section )
>>> 355     {
>>> 356         p = xen_elfnote_string(dsi, XEN_ELFNOTE_PAE_MODE);
>>> 357         if ( p != NULL && strncmp(p, "yes", 3) == 0 )
>>> 358             dsi->pae_kernel = PAEKERN_extended_cr3;
>>>
>>> Could we have a new note instead?
>> I don't think it improves the situation, for older Xens you need two
>> kernels anyway, even if the only difference is the content of the
>> pae_mode elf note ...
> 
> What do you mean? Are you saying that Xen complains about an ELF note it
> doesn't understand?

No.

Moving the bimodal flag to another elf node doesn't fix the problem that
older Xen versions don't support bimodal kernels, thus you still need a
pae and a non-pae kernel.  As older Xens consider bimodal kernels as
non-pae one bimodal and one pae kernel works too.  But you can't get
that down to only one kernel unless you drop support for xen versions
below 3.0.4 ...

cheers,
  Gerd

-- 
Gerd Hoffmann <kraxel@suse.de>