Bug#776911: gnome-shell: fails to start on i386 when [Mesa was] built with llvm-3.5

[Kill Your TV]

On Tue, 10 Mar 2015 08:16:03 +0000 (UTC)
Simon McVittie <smcv at debian.org> wrote:

> On 09/03/15 22:30, Kill Your TV wrote:
> > On Mon,  9 Mar 2015 21:04:55 +0000 (UTC)
> > Simon McVittie <smcv at debian.org> wrote:
> >> If your host CPU is missing any of those features, then emulating a
> >> SandyBridge CPU in your VM is probably an invalid configuration.
> > 
> > This is absolutely true of course (I personally use -cpu host), but
> > IMHO there should be more graceful handling of the situation,
> > falling back to something that will almost certainly work.
> 
> That's fine, but I don't think it's release-critical. Could you file a
> separate bug for that part, please?

Agreed, it's definitely not release critical if it works on *real*
hardware now. :) I'll gladly file a new bug for this.

> (I also think that's a qemu bug, more than an application bug; it
> shouldn't let you emulate a CPU that isn't going to work. I don't
> think applications should be expected to cope gracefully with an
> emulated CPU that claims it can support instructions but does not
> actually execute them correctly, which I think is what's going on in
> this case.)

I'd wholeheartedly +1 this is the failure was only on emulated systems
with "impossibly-doomed-to-failure" configurations, but from the
earlier posts in this bug this problem initially affected real hardware.
Perhaps it's not gnome-shell that should be responsible for handling
the problem more gracefuly but something down the line should, be it
mesa or something else.

(gnome-shell should, however, give a more informative error when things
go wrong but that's for another bug report, one which probably already
exists).

I'm not saying that there isn't also a qemu bug as well. Indeed, if qemu
is expected to virtualize a particular configuration it should be able
to either do it or fail early with a clear message explaining why it
failed. "Your host CPU is missing the necessary features to be
able to emulate the CPU-type specified". 

But as far as *this* bug is concerned, I'm satisfied with the patch to
mesa since that fixes the problems that I experienced with valid
configurations.
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