On 03/18/2014 05:00 AM, Jiri Denemark wrote:
>> 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 $@
>
> That's what I tried first but it does not work at all. I don't
> understand why but make thinks cpu/cpu_map.xml target is uptodate even
> though the file does not exist in builddir.
That would be VPATH rewriting at play. Does $(builddir)/cpu/cpu_map.xml
fare any better?
> And $(srcdir) doesn't work
> for relative VPATH. For example, if VPATH is .., then
>
> abs_srcdir = /some/path/src
> abs_builddir = /some/path/build/src
> srcdir = ../../src
>
> and the /some/path/build/src/cpu/cpu_map.xml link will be
> ../../src/cpu/cpu_map.xml and thus will point to itself.
$(srcdir) is not the problem - that part of the rule can be written
absolute as follows:
$(AM_V_GEN)ln -s `cd $(srcdir) && pwd`/cpu/cpu_map.xml $@
It's just the $(abs_builddir) we're trying to figure out if we can avoid.
> And we can't
> just blindly do
>
> ln -s ../$(srcdir)/cpu/cpu_map.xml $@
>
> because this would not work for absolute VPATH, when srcdir is
> /some/path/src.
>
> Yeah, it's a mess.
I looked at gnulib for inspiration, because it also does a symlink of
GNUmakefile when doing a VPATH build while using the original file when
doing in-tree. But it was depressing: it doesn't work for VPATH builds
on RHEL 5:
configure.ac:
# Autoconf 2.61a.99 and earlier don't support linking a file only
# in VPATH builds. But since GNUmakefile is for maintainer use
# only, it does not matter if we skip the link with older autoconf.
# Automake 1.10.1 and earlier try to remove GNUmakefile in non-VPATH
# builds, so use a shell variable to bypass this.
GNUmakefile=GNUmakefile
m4_if(m4_version_compare([2.61a.100],
m4_defn([m4_PACKAGE_VERSION])), [1], [],
[AC_CONFIG_LINKS([$GNUmakefile:$GNUmakefile], [],
[GNUmakefile=$GNUmakefile])])
Makefile.am:
distclean-local: clean-GNUmakefile
clean-GNUmakefile:
test '$(srcdir)' = . || rm -f $(top_builddir)/GNUmakefile
But maybe that's some food for thought - instead of having a rule that
uses a direct file name, perhaps you can instead have a witness rule on
a stamp file name, where we write the link ourselves when needed, and
then have all dependencies be on the stamp (which will ALWAYS exist only
in builddir):
cpu/cpu_map.xml.stamp:
$(AM_V_GEN)if test -f cpu/cpu_map.xml; then \
:; else \
ln -s `cd $(srcdir) && pwd`/cpu/cpu_map.xml \
cpu/cpu_map.xml; \
fi && touch $@
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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