Re: [Qemu-devel] converting build system to Meson?

From: "Daniel P. Berrangé" <berrange@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Thomas Huth" <thuth@redhat.com>,
	qemu-devel <qemu-devel@nongnu.org>,
	"Peter Maydell" <peter.maydell@linaro.org>,
	"Marc-André Lureau" <marcandre.lureau@redhat.com>,
	"Richard Henderson" <rth@twiddle.net>
Subject: Re: [Qemu-devel] converting build system to Meson?
Date: Thu, 7 Mar 2019 10:49:38 +0000	[thread overview]
Message-ID: <20190307104938.GM32268@redhat.com> (raw)
In-Reply-To: <13c59d63-1761-b61e-9cb9-039a3ef1be08@redhat.com>

On Thu, Mar 07, 2019 at 11:40:05AM +0100, Paolo Bonzini wrote:
> On 07/03/19 07:39, Thomas Huth wrote:
> > On 06/03/2019 19.12, Paolo Bonzini wrote:
> >> Hi all,
> >>
> >> lately I have been thinking of converting the QEMU build system to
> >> Meson.  Meson is a relatively new build system that can replace
> >> Autotools or hand-written Makefiles such as QEMU; as a die-hard
> >> Autotools fan, I must say that Meson is by far better than anything else
> >> that has ever tried to replace Autotools, and actually has the potential
> >> to do so.
> >>
> >> Advantages of Meson that directly matter for QEMU include:[...]
> > 
> > I'm not objecting a new build system per se, but could you elaborate on
> >  problems of the current QEMU build system that will be fixed by this
> > change?
> 
> In order of importance:
> 
> - Make lacks introspection abilities; people want to be able to quickly
> say "I don't have this security issue because I didn't compile this
> file".  Make only gives you the build logs, which may not be easily
> accessible to the end user.
> 
> - Makefile.objs unnesting does not apply throughout the tree, for
> example it does not apply to tests.  We don't apply it there because it
> it is hard to extend Makefile.objs to dozens of targets and it would
> also be very very slow.  The result is lack of homogeneity between
> places that use Makefile.objs and places that use Makefile.include.
> 
> - Makefile.objs unnesting is hard to understand---granted, you rarely
> have to understand it because it mostly works, but we should consider
> whether it is a local optimum.  For example, how many people know how to
> add a dynamically-loadd module to Makefile.objs?

We have a long standing bug in unnesting which breaks if two dirs
have a .c file with the same name and a per-o file library link:

  https://lists.gnu.org/archive/html/qemu-devel/2018-06/msg02654.html

The nesting stuff is insanely clever, but it is also fragile and full
of dragons like this one.

Regards,
Daniel
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