Re: Generated Makefiles for multiple platforms

[Ralf Wildenhues]

Hi Ben,

* BRM wrote on Sun, Dec 18, 2005 at 10:15:20PM CET:
> After reading through all the wisdom that has been
> given to me by this list, I have modified my test
> project to (a) generate all the Makefiles statically:
> 
> AC_OUTPUT(Makefile, os/Makefile, os/linux/Makefile,
> os/mingw32/Makefile, etc.)
> 
> I also added some AM_CONDITIONALs for each supported
> OS to my configure.ac like the following:
> 
> AM_CONDITIONAL([TARGET_LINUX],[test ¨$target_os¨ =
> ¨linux¨])
> 
> However, I am still having a few issues that I can´t
> figure out. Namely - ´make´ doesn´t want to recurse if
> I have the following in my os/Makefile.am:
> 
> if TARGET_LINUX
>    COMILE_OS = ¨linux¨

Please remove the quotes here, and note the typo.
     COMPILE_OS = linux

> endif
> ...
> SUBDIRS = $(COMPILE_OS)

This should work.

> It will recurse if I change it to the following:
> 
> SUBDIRS = @target_os@

automake needs to know the set of possible SUBDIRS at the time automake
runs (which means substitutions like @foo@ are forbidden) in order to
compute DIST_SUBDIRS, so this won't work.  It should be possible to work
around this by setting DIST_SUBDIRS manually to all possible SUBDIRS.

By the way, this is very well documented in 
http://sources.redhat.com/automake/automake.html#Conditional-Subdirectories

> I am also having trouble getting make to build the
> object file inside of the os/@target_cpu@ directory.
> If I do get it to recurse in, it returns with a
> ´all-am nothing to do´ type message without having
> build the os.o file. I have tried doing things like
> the following:
> 
> hello_world_SOURCES = os.c
> 
> SOURCES = os.c
> 
> os_SOURCES = os.c
> 
> however, in the case of ´SOURCES = os.c' is just
> doesn´t do anything. In the other two, it complains
> with the following:
> 
> variable ´hello_world_SOURCES´ defined but no program
> or library has ´hello_world´ as canonic name (possible
> typo).

The question is: sources of what?  Do like this:

bin_PROGRAMS = hello_world
hello_world_SOURCES = os.c

If your os.c should not end up in a program, you could make it be a
source of a static library, or a shared library, or a convenience
library.

Cheers,
Ralf