From mboxrd@z Thu Jan  1 00:00:00 1970
From: Olaf Hering <olaf@aepfle.de>
Subject: Re: [PATCH 02/13] Config.mk: replace dependency to
 genpath with actual target
Date: Wed, 27 Aug 2014 10:36:48 +0200
Message-ID: <20140827083648.GA5892@aepfle.de>
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To: Ian Campbell <ian.campbell@citrix.com>
Cc: Keir Fraser <keir@xen.org>, Stefano Stabellini <stefano.stabellini@eu.citrix.com>, Tim Deegan <tim@xen.org>, Ian Jackson <ian.jackson@eu.citrix.com>, xen-devel@lists.xen.org, Jan Beulich <jbeulich@suse.com>, Samuel Thibault <samuel.thibault@ens-lyon.org>
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On Tue, Aug 26, Ian Campbell wrote:

> On Mon, 2014-07-28 at 11:05 +0200, Olaf Hering wrote:
> 
> Sorry for the delay in looking into this, I've been on vacation and
> travel.
> 
> > genpath is a detail of buildmakevars2file. Replace the dependency to
> > genpath with the actual buildmakevars2file target. This change by
> > itself does not fix any bug. Upcoming changes will add dependencies to
> > $(target), but no rule exist to create $(target).
> > 
> > No change in behaviour is expected by this patch.
> > 
> > Note: target.tmp ($(1).tmp) is not marked as .PHONY because
> > move-if-changed in the target rule will remove target.tmp by renaming
> > it to target. As a result make will always attempt to rebuild it.
> 
> Does the scheme you've got here end up differing from:
> 
>     $(1):
>        rm -f $(1).tmp; \
>         $(foreach var, $(BUILD_MAKE_VARS), \
>                  echo "$(var)=\"$($(var))\"" >>$(1).tmp;) \
>         $(call move-if-changed,$(1).tmp,$(1))
> 
> (i.e. avoiding the $(1).tmp rule)

In my testing make did always rebuild the targets depending on _paths.h
for example. The reason is that _paths.h is .PHONY, which cause make to
drop _paths.h and see it as new, even if the content did not change. 
With _paths.h.tmp being .PHONY _paths.h remains the same for make.

Not sure why that happens, perhaps thats how .PHONY works.

Olaf