Re: [Xen-devel] [BUG?] qemuu only built with i386-softmmu

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Fri, 2016-02-05 at 08:09 +1100, Steven Haigh wrote:
> In building my Xen 4.6.0 packages, I disable qemu-traditional and ONLY
> build qemu-upstream - however as the value for i386-softmmu is not based
> on variables, I'm not sure this makes a difference.

QEMU in a Xen system only provides device model (DM) emulation and not any
CPU instruction emulation, so the nominal arch doesn't actually matter and
Xen build's i386 everywhere as a basically arbitrary choice.

It happens that the Xen DM part of QEMU is quite closely tied to the x86
scaffolding for various historical reasons, so we end up using qemu-system-
i386 even e.g. on ARM!

This comes up a lot, So I've also pasted the two paras above into a new
section inÂhttp://wiki.xenproject.org/wiki/QEMU_UpstreamÂ;. If anyone thinks
the above is inaccurate then please edit the wiki (and post here too if you
like).

On thing I was sure on (so didn't write) is whether the second paragraph
could have an extra sentence:

    If you are using a distro supplied QEMU then the qemu-system-x86_64
    could also be used, but it makes no practical difference to the
    functionality of the system.

I wasn't sure if that was true (I suspect it is) and in any case I think
various bits of libxl etc will look for qemu-system-i386 in various paths
so a user would need to try reasonably hard to do so by giving an explicit
path and there is no real reason to do so maybe better not to muddy the
waters?

Ian.

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