Re: library dependencies SUBDIR problem automake

[John Calcote]

Hi Michiel,

On 8/4/2009 10:01 AM, Michiel Soede wrote:
> Hi,
> I have a problem with dependencies to libraries in my build structure.the 
> directory structure in my project is as follows (roughly):
>
> configure.acmakefile.amapps/         makefile.am         app1/               
> main.cc               makefile.am       comps/         makefile.am         
> comp1/               comp1.cc               makefile.am
> the component makefile generates a library:noinst_LIBRARIES = 
> libcomp1.alibcomp1a_a_SOURCES = comp1.cc
> I recurse in all subdirectories, using SUBDIRS:SUBDIRS = apps comps
> in the comps:SUBDIRS = comp1
> same for the apps directory.
> the app1 uses LDADD to link the app with main.cc
> bin_PROGRAMS = app1app1_SOURCES = main.ccapp1_LDADD = 
> $(top_builddir)/comps/comp1/libcomp1.a
> Now when I call make at the root, everything is build correctly.
> But when I cd into apps/app1/ and call make, I have problems with:
> - if comp1 was not made before (e.g. from the root), make will fail  (no rule 
> to make libcomp1.a)
> - if I did make the library at the root, it is not recompiled automatically 
> when  I modify comp1.cc
> .. any ideas on these problems?
>    
The lack of proper text wrapping on your message made it a bit difficult 
to see your directory structure, but I think I've sorted it out, based 
on your other comments:

configure.ac
makefile.am
apps/
  makefile.am
  app1/
    main.cc
    makefile.am
comps/
  makefile.am
  comp1/
    comp1.cc
    makefile.am

According to your makefiles, app1 is dependent on comp1 (app1_LDADD = 
.../libcomp1.a), but comp1 is not built as a sub-component 
(sub-directory) of app1. Thus, (I believe you are saying) when you build 
from the project root, everything is fine, but when you build from the 
app1 directory, comp1 doesn't get built, and thus the app1 build fails. 
Is this correct?

A recursive build system must be designed to build component 
dependencies first before building the components. Thus, one limitation 
of a recursive build system is that it rather defines (or at least 
constrains) the directory structure that you must use. To get comps to 
be built before apps from within the app1 directory, you must build the 
comps directory structure from within the app1 directory.

I recognize that applications 2-n may also use components 1-n, so you 
have a problem here, and the only way around it is to use a 
non-recursive build system. That is, you can place all of your build 
logic in the top-level Makefile.am file using relative paths, and then 
the makefile dependencies will be properly structured for you by Automake:

Makefile.am:
= = = = = = = = = = =
bin_PROGRAMS = app1 app2 app3 ...
app1_SOURCES = apps/app1/main.cc
app2_SOURCES = apps/app2/...
...

noinst_LIBRARIES = libcomp1.a libcomp2.a libcomp3.a ...
libcomp1_a_SOURCES = comps/comp1/comp1.cc
libcomp2_a_SOURCES = comps/comp2/...
...

app1_LDADD = libcomp1.a
= = = = = = = = = = =

I also noted that you had

SUBDIRS = apps comps

in your top-level Makefile.am file. This is wrong - the comps hierarchy 
should be built before the apps hierarchy, or else there will still be 
no libraries in the comps hierarchy for the apps to link against, unless 
you've manually built the comps directory first, and then attempted to 
build from root.

Regards,
John