How to write a simple hierarchical Makefile?

Question

Some days ago I posted an answer in stack overflow about how to write a hierarchical make (http://stackoverflow.com/questions/1498213/make-hierarchical-make-file). The answer was deleted, therefore I assume that it was completely wrong or off topic (or both).

I would like to know how to write hierarchical Makefile. This is a Makefile that calls several Makefiles in sub-directories. I assume a directory structure like:

- project
  |--module1
      |--Makefile
      |--...
  |--module2
     |--Makefile
     |--module2.1
     |--module2.2  
     |--...
  |--module3
     |--Makefile
     |--...
  |--etc

I also assume that the project members have only agreed only upon a minimal set of makefile targets like: all (default), clean, install, and so. So, the following commands including make flags will be propagate to the modules:

cd project
make clean  
make -k
make install
#etc

What is wrong with the following project Makefile:

PACKAGES = \
    module1 \
    module2 \
    emodule3

VIRTUAL_PACKAGES = $(addsuffix /.virtual.Makefile,${PACKAGES})

TARGETS=clean install all

.PHONY: $(TARGETS)
default: all

FLAGS = $(ifeq $(MAKEFLAGS) "","",-$(MAKEFLAGS))

$(TARGETS): $(VIRTUAL_PACKAGES)

$(VIRTUAL_PACKAGES): 
    $(MAKE) $(FLAGS) -C $(@D) $(MAKECMDGOALS)

yes, the $VIRTUAL_PACKAGES in the Makefile looks odd. The alternative of mixing a for loop is a bit shorter but I am not sure if it is better (as I need to rely on bash): PACKAGES = \ module1 \ module2 \ emodule3

TARGETS=clean install all

.PHONY: $(TARGETS)
default: all

FLAGS = $(ifeq $(MAKEFLAGS) "","",-$(MAKEFLAGS))

$(TARGETS): 
    for p in $(PACKAGES) ; do $(MAKE) $(FLAGS) -C $$p $@ || break; done

Thanks!

Answer 1

There are "dragons" here. It can be done, but the implications can be tricky.

Google, "Recursive Make Considered Harmful". You will get very good (simple) illustrations of exactly what you want (e.g., hierarchical-make), plus good explanations of the pitfalls/concerns. Some of the "responses" will discuss possible "best-practices", and ways to mitigate problems. Then, you can decide if the issues raised are compelling for your application or not.

The original paper:

http://miller.emu.id.au/pmiller/books/rmch/

Some other links:

http://c2.com/cgi/wiki?RecursiveMakeConsideredHarmful

http://dbaspot.com/configuration-management/194597-thoughts-recursive-make-considered-harmful.html