Re: [Xen-devel] [PATCH RFC v1 06/74] tools/libelf: fix elf notes check for PVH guest

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Jan 04, 2018 at 07:37:20AM -0700, Jan Beulich wrote:
> >>> On 04.01.18 at 14:05, <wei.liu2@xxxxxxxxxx> wrote:
> > PVH only requires PHYS32_ENTRY to be set. Return immediately if that's
> > the case.
> 
> So I guess the bug(?) being fixed is that so far loader or guest_os,
> and xen_ver settings are also required. However, you fail to mention
> _why_ you think they're not required. I can sort of see this for
> loader and maybe guest_os, but for the Xen version this isn't as
> obvious, mainly because any arguments I can think of right now
> would equally apply to PV.

Got it from docs/misc/pvh.markdown. It doesn't state other notes are
required.

I'm not sure if xen_version (always "xen-3.0"?) will be meaningful or
useful. It is not the end of the world if we check it but we do need to
be careful to not break existing OSes (mini-os for one only sets
PHYS32_ENTRY for PVH mode but that's easy to fix).

> 
> > --- a/xen/common/libelf/libelf-dominfo.c
> > +++ b/xen/common/libelf/libelf-dominfo.c
> > @@ -381,6 +381,13 @@ static elf_errorstatus elf_xen_note_check(struct 
> > elf_binary *elf,
> >           return 0;
> >      }
> >  
> > +    /* PVH only requires one ELF note to be set */
> > +    if ( parms->phys_entry != UNSET_ADDR32 )
> > +    {
> > +        elf_msg(elf, "ELF: Found PVH image\n");
> > +        return 0;
> > +    }
> 
> If the other entries are of no interest for PVH, I think that this
> then calls for dropping their logging from pvh_load_kernel().

Sure.

> I'm also surprised that I can't find any use of any of the three
> values checked in libxc.

Libxc delegates the work to libelf AIUI.

Wei.

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