Debugging makefile s is somewhat of a black art. Unfortunately, there is no such thing as a makefile debugger to examine how a particular rule is being evaluated or a variable expanded. Instead, most debugging is performed with simple print statements and by inspection of the makefile . GNU make provides some help with various built-in functions and command-line options.
One of the best ways to debug a makefile is to add debugging hooks and use defensive programming techniques that you can fall back on when things go awry. I'll present a few basic debugging techniques and defensive coding practices I've found most helpful.