Re: [Qemu-devel] [PATCH] hw/xen/xen_pvdev: Include qemu/log.h for qemu_log_vprintf()

[Stefano Stabellini]

On Wed, 2 Nov 2016, Peter Maydell wrote:
> On 2 November 2016 at 17:34, Stefano Stabellini <address@hidden> wrote:
> > On Wed, 2 Nov 2016, Thomas Huth wrote:
> >> Olaf Hering reported a build failure due to an undefined reference
> >> to 'qemu_log_vprintf'. Explicitely including qemu/log.h seems to
> >> fix the issue.
> >>
> >> Signed-off-by: Thomas Huth <address@hidden>
> >
> > The fix makes sense:
> >
> > Acked-by: Stefano Stabellini <address@hidden>
> >
> > However I was unable to reproduce the build failure, so I would like a
> > confirmation from Olaf that the fix is working.
> 
> If you configure with the (default) simple trace
> backend then trace.h will pull in qemu/log.h
> (and in this case trace.h comes in via xen_common.h).
> But if you're using a different backend then it won't
> bring in that header, and you'll get the build failure.
> 
> This is a fairly common "breaks but only with
> some trace backends" compile failure, but I'm
> not sure how best to try to make it more robust
> (or at least into a 'fails-everywhere' bug).

Personally what I can do is adding

  --enable-trace-backends=syslog

to my test scripts. That is enough to repro the issue. Thanks for the
explanation.