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Date: Mon, 09 May 2011 08:53:17 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-trivial] [PATCH 4/4] fix compilation when reconfiguring
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On 05/08/2011 01:15 PM, Stefan Hajnoczi wrote:
> I think the real problem is that dependencies need to be regenerated
> after ./configure?

There are three ways to do that, the trivial but wrong one, and the 
correct but overzealous one:

- delete .d files.  This forces regeneration of dependencies, but if you 
do not correspondingly delete .o files, you will likely have an 
incomplete build (possibly _nothing_ will be built).

- delete .d and .o files.  This forces regeneration of dependencies and 
recompilation.  True, a lot of distros are using ccache nowadays, but 
still this will cause a complete walk of all directories to pass those 
files to ccache and relink the executables.  It will likely take a 
minute or three.

- detect changes in the configuration and, if those happen, delete .d 
and .o files.  This is the correct one, and for one what the Linux 
kernel makefiles do, but also the biggest effort to implement.

Paolo