Re: [Xen-devel] [Draft B] Boot ABI for HVM guests without a device-model

[Roger Pau Monnà <roger.pau@xxxxxxxxxx>]

El 26/08/15 a les 14.12, Andrew Cooper ha escrit:
> On 26/08/15 13:00, Jan Beulich wrote:
>>> This structure is guaranteed to always be placed in memory after the
>> DYM "These structures are ..."?
>>
>>> loaded kernel and modules.
> 
> There is no requirement for the command line/module information to be
> after the loaded kernel.  All it needs to do is not overlap.

IMHO, this is helpful in order to get last used physical address, after
which free memory starts. Current FreeBSD implementation relies on this,
if we didn't do it that way I would have to calculate where the symtab +
strtab ends, which is more complex.

>>>  There's no upper bound on the size of the
>>> structure, users should be aware that it might cross a page boundary.
>> How is there no size limit? It's (currently) 16 bytes, and I don't see
>> why it would change. And even if - as implied by the previous
>> comment - this also relates to struct hvm_start_info: Its size is
>> fixed (and unlikely to change much) too.
> 
> I agree it is unlikely to change (but there is a flags field just in
> case), but we shouldn't impose unnecessary arbitrary restrictions.

After reading it again, I realize this is not properly worded. What I
wanted to say is that the cmdline or the list of loaded modules might
cross a page boundary.

Roger.


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