Re: Feature Request: Improved cross-directory builds (intermediate files)

[Ralf Wildenhues]

* Bollinger, John C wrote on Fri, Sep 11, 2009 at 09:09:18PM CEST:
> > Automake's cross-directory support seems to have at least one serious
> > problem, however: Makefiles generated by the autotools always build
> > intermediate objects in the top source directory.  For example, if I
> > am building ./subpackage1/foo from ./subpackage1/foo.c and
> > ./subpackage1/init.c, then the intermediate foo.o and init.o files are
> > created in the top source directory (./foo.o and ./init.o), instead of
> > in ./subpackage1/.  Aside from the mess, this presents a grave risk of
> > incorrect builds, for if I also have subpackage2/init.c (or
> > subpackage2/init.f, etc.) then that wants to use the same name and
> > location for its intermediate .o file as does subpackage1/init.c.

Besides subdir-objects, automake should also warn you about this
situation:
| Makefile.am: object `foo.$(OBJEXT)' created by `s2/foo.c' and `s1/foo.c'

and per-target flags should cause a renaming of the object.

> So color me embarrassed:  the 'subdir-objects' Automake option appears
> to do what I want, more or less(*).  Inasmuch as it is particularly
> relevant there, perhaps a mention of it could be added to section 7.3
> of the manual?

Yes, that sounds like a good idea.

> (*) "More or less" because with Automake 1.11 it yielded Makefiles containing 
> many lines of the form
>         include src/$(DEPDIR)/foo.Po
> These files did not (yet) exist, so make completely rejected the file.
> Automake stopped emitting these when I removed the 'subdir-objects'
> option, and started again when I put it back.

That's weird, because there should be (undocumented)
src/$(DEPDIR)/$(am__dirstamp) targets in the Makefile which the .deps
file depend upon and which cause the directories to be created in the
build tree.  Can you show a (preferably small) reproducible test case
please?  Thanks.

>  In the end I added the
> 'no-dependencies' option as well; this suppressed the include lines,
> but of course also disabled dependency tracking.

This shouldn't be necessary.

Cheers,
Ralf