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Re: deprecation of in-tree builds

From: Peter Maydell
Subject: Re: deprecation of in-tree builds
Date: Sun, 22 Mar 2020 21:15:25 +0000

On Sun, 22 Mar 2020 at 20:46, BALATON Zoltan <address@hidden> wrote:
> On Sun, 22 Mar 2020, Peter Maydell wrote:
> > Before you told me about the gprof issue, the *only* thing
> Was that gprof or gcov?

Sorry, gcov; I always get those two mixed up in my head.

> Plus potentially any scripts people might use to build stuff and distro
> packagers that might use in-tree build. They would suddently find their
> previously working scripts are now broken and they need to adapt.

It is to avoid the "suddenly" part that we announce in advance
that features are going away :-)  More generally, distro packagers
must adapt for any new QEMU release -- new features appear that
they may need to update their dependency lists to handle, old
features are sometimes removed and the corresponding configure
--enable-foo options stop working, existing features need new

Also, we've been recommending out-of-tree builds in our README
since 2015. They're hardly a new thing.

> While
> making sure running configure; make; make install in source tree even if
> it actually does a build in a new build dir it creates automatically would
> be less annoying change than having to manually manage out-of-tree build
> dirs by those who did not do that so far.
> Is it really that difficult to add a CI job to do a git clone then
> configure; make; make install in it to make sure it breaks less often?

To be honest, I don't feel very strongly here, except that
I didn't want us to drop in-tree builds without noting it
in the release notes, and my impression from previous list
discussions was that that was the way the project was heading.

If somebody wants to write patches to cause 'configure' to create
a new build tree that's OK I guess (though I'd be dubious because
I think that hidden magic like that is overall often going
to confuse people, and it's still extra machinery in the
makefile and the configure script). But I don't really see
much point in maintaining two different mechanisms which add
complication and where one of them is just not overall as useful
as the other.

I fairly often see posts from people on eg stackoverflow
who are trying to compile and modify QEMU, and they're
usually using in-tree build and I usually mention in a
PS to answering their question that they'd really be
better off with an out-of-tree build. I think we should
stop making it easy to default to a setup that we don't

-- PMM

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