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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Thu, 2015-11-12 at 16:02 +0000, Andrew Cooper wrote:
> On 12/11/15 12:47, Ian Campbell wrote:
> > On Thu, 2015-11-12 at 12:37 +0000, Andrew Cooper wrote:
> > > 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.ÂÂThis has nothing to do with DMLite guests, so no
> > > elfnotes are involved.
> > > 
> > > I realise that strictly speaking the elf check should
> > > match.ÂÂHowever,
> > > 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.)
> > An ELF file which says it is class ELF32 but has 64bit code at the
> > entry
> > point is IMHO malformed.
> > 
> > I think that the fact this used to work is a misfeature, however
> > convenient
> > you may have found it.
> > 
> > Kernels which wish to do this should IMHO do as Xen does and have a
> > mkelf32.c step. You can still run gdb or whatever using the original
> > ELF
> > file.
> 
> It turns out that
> 
> OUTPUT_FORMAT("elf32-x86-64")
> 
> is a thing for linker scripts.
> 
> I have updated the framework to use that for 64bit hvm tests, and
> everything appears to be working.

Great. I shall consider this patch withdrawn then.

Thanks for letting us know.

Ian.


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