Re: how to do recursive "subsystem" make properly?

[Christophe LYON]

Hi Paul,

>         prog: foosrc/libfoo.a
>                 ...do something...
>
>         foosrc/libfoo.a: FORCE
>                 $(MAKE) -C foosrc
>
>         FORCE: ;
>
> In this model, libfoo.a will always be considered out of date (because
> of the FORCE prerequisite--just be sure you don't create a file "FORCE"
> in your directory), so the command to build it will be invoked.  The
> command is the submake.
>
> If the submake actually updates libfoo.a, then "prog" will be rebuilt.
> If the submake does not change libfoo.a, then "prog" will not be
> considered out of date.

Sorry if the answer is obvious, but I don't understand why "prog" isn't 
simply always rebuilt, because libfooa is always updated. Is it because 
the command is $(MAKE)?

(Replacing $(MAKE) -C foosrc by touch $@ actually implies that prog is 
always updated)

It tried to find something about this in the documentation, but I failed.

Thanks

Christophe.