I am looking for suggestions to properly handle separate debug and release build subdirectories, in a recursive makefile system that uses the $(SUBDIRS) target as documented in the gnumake manual to apply make targets to (source code) subdirectories.
Specifically, I’m interested in possible strategies to implement targets like ‘all’, ‘clean’, ‘realclean’ etc. that either assume one of the trees or should work on both trees are causing a problem.
Our current makefiles use a COMPILETYPE variable that gets set to Debug (default) or Release (the ‘release’ target), which properly does the builds, but cleaning up and make all only work on the default Debug tree. Passing down the COMPILETYPE variable gets clumsy, because whether and how to do this depends on the value of the actual target.
One option is to have specific targets in the subdirectories for each build type. So if you do a ‘make all’ at the top level, it looks at COMPILETYPE and invokes ‘make all-debug’ or ‘make all-release’ as appropriate.
Alternatively, you could set a COMPILETYPE environment variable at the top level, and have each sub-Makefile deal with it.
The real solution is to not do a recursive make, but to include makefiles in subdirectories in the top level file. This will let you easily build in a different directory than the source lives in, so you can have build_debug and build_release directories. It also allows parallel make to work (make -j). See Recursive Make Considered Harmful for a full explanation.