Re: [libvirt] [PATCH] build: Fix build with old automake

On Tue, Mar 18, 2014 at 11:36:51AM +0100, Jiri Denemark wrote: > On Mon, Mar 17, 2014 at 09:33:11 -0600, Eric Blake wrote: > > On 03/14/2014 12:55 PM, Jiri Denemark wrote: > > > On Fri, Mar 14, 2014 at 07:54:58 -0600, Eric Blake wrote: > > >> On 03/14/2014 04:43 AM, Jiri Denemark wrote: > > >>> Ancient automake (such as from RHEL5) does not provide abs_srcdir and > > >>> abs_builddir variables which are used by a recent commit of mine > > >>> (e562e82). > > >>> > > >>> Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com&gt; > > >>> --- > > > > >>> +# old automake does not provide abs_{src,build}dir variables > > >>> +abs_builddir = $(shell pwd) > > >>> +abs_srcdir = $(shell cd $(srcdir) && pwd) > > > > Hmm, just noticed another thing - with NEWER automake, we are now less > > efficient (calling out to $(shell) overwrites the value that is already > > provided for free without a subprocess by newer automake). Does it work > > if you use: > > > > abs_builddir ?= $(shell pwd) > > Automake does a fair amount of magic here so abs_builddir = $(shel ...) > does not actually overwrite the old value because there is no old value > :-) Automake just does not put it's own abs_builddir definition in that > case. If I switch to abs_builddir ?= $(shell ...), automake adds it's > own definition so it seems it could work except that it doesn't. With > "=", automake adds the definition above the other variable definition > and namely above libvirt_cpu_la_DEPENDENCIES which uses it: > > abs_builddir = $(shell ...) > ... > libvirt_cpu_la_DEPENDENCIES = $(abs_builddir)/... > ... > rules > > When I switch to "?=", automake apparently does not recognize it as a > variable definition and puts it between the block with variable > definitions and rules. Thus the result is: > > abs_builddir = /some/build/path > ... > libvirt_cpu_la_DEPENDENCIES = $(abs_builddir)/... > ... > abs_builddir ?= $(shell ...) > ... > rules > > which of course does not work with old automake which does not add the > first abs_builddir definition there and thus libvirt_cpu_la_DEPENDENCIES > sees $(abs_builddir) empty. > > Anyway, making two extra shell commands once per build does not seem > like anything we should really care about so I'd just stick with > > abs_builddir = $(shell ...) Why don't we just avoid the whole issue by removing use of abs_srcdir and abs_builddir. Can this rule: $(abs_builddir)/cpu/cpu_map.xml: $(AM_V_GEN)ln -s $(abs_srcdir)/cpu/cpu_map.xml $@ be just changed to cpu/cpu_map.xml: $(AM_V_GEN)ln -s $(srcdir)/cpu/cpu_map.xml $@