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[Xen-devel] Re: [xen-4.0-testing bisection] complete build-amd64

To: "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>, "keir@xxxxxxx" <keir@xxxxxxx>, Stefano Stabellini <Stefano.Stabellini@xxxxxxxxxxxxx>, Olaf Hering <olaf@xxxxxxxxx>
Subject: [Xen-devel] Re: [xen-4.0-testing bisection] complete build-amd64
From: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
Date: Mon, 23 May 2011 15:01:52 +0100
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Ian Jackson writes ("[xen-4.0-testing bisection] complete build-amd64"):
> *** Found and reproduced problem changeset ***
>   Bug is in tree:  http://hg.uk.xensource.com/xen-4.0-testing.hg
>   Bug introduced:  19eefd764f6f
>   Bug not present: c6034ee9b46e
>   changeset:   21492:19eefd764f6f
>   user:        Olaf Hering <olaf@xxxxxxxxx>
>   date:        Sat May 21 07:57:03 2011 +0100
>       gcc-4.6 compile fix: build with -Wno-unused-but-set-variable
>       Avoid "error: variable 'unused' set but not used
>       [-Werror=unused-but-set-variable]" with gcc 4.6.
>       Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
>       xen-unstable changeset:   23368:0f670f5146c8
>       xen-unstable date:        Sat May 21 07:55:46 2011 +0100

Leaving aside the debugging of the reason for this:

I think this demonstrates that it's a bad idea to backport changes
immediately from xen-unstable into earlier trees.

Changes which allegedly fix build system or OS incompatibilties are
particularly bad for this, because it is those changes which are
themselves most likely to (a) have hard to predict outcomes (b) break
the build (c) in a way not detected by a developer's smoke test.


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