Re: [PATCH] tools/libxc: Fix construction of HVM guests with non-default firmware

[Andrew Cooper <andrew.cooper3@citrix.com>]

On 12/11/15 09:41, Ian Campbell wrote:
> On Wed, 2015-11-11 at 20:18 +0000, Andrew Cooper wrote:
>> c/s 1ee15d7 "libxl: switch HVM domain building to use xc_dom_* helpers"
>> introduced a regression building HVM domains in combination with the
>> libxl
>> "firmware_override=" option.
>>
>> The older HVM building code (now removed) had no 32bit ELF check, so would
>> happily load ELF64 images which contained a stub to switch into long mode.
> IOW a ELF64 with 32-bit code at its entry point? Is that entry point the
> ELF entry point or the special Xen entry point located via the notes?
>
> I think you likely mean the latter, in which case I'm ok with this change
> if that entry point is explicitly documented to be 32-bit irrespective of
> the containing ELF file (either the commit message should mention this is 
> already the case or the patch should update the docs to make it so).

I mean the former.  This has nothing to do with DMLite guests, so no
elfnotes are involved.

I realise that strictly speaking the elf check should match.  However,
it always used to work, and is sufficiently convenient for development
purposes that I feel the check is more problematic than helpful. 
(Postprocessing the linked binary from 64bit to 32bit elf is an extra
step which also makes it harder to disassemble.)

~Andrew