GNU Make - Dependencies on non program code
- by Tim Post
A requirement for a program I am writing is that it must be able to trust a configuration file. To accomplish this, I am using several kinds of hashing algorithms to generate a hash of the file at compile time, this produces a header with the hashes as constants.
Dependencies for this are pretty straight forward, my program depends on config_hash.h, which has a target that produces it.
The makefile looks something like this :
config_hash.h:
$(SH) genhash config/config_file.cfg > $(srcdir)/config_hash.h
$(PROGRAM): config_hash.h $(PROGRAM_DEPS)
$(CC) ... ... ...
I'm using the -M option to gcc, which is great for dealing with dependencies. If my header changes, my program is rebuilt.
My problem is, I need to be able to tell if the config file has changed, so that config_hash.h is re-generated. I'm not quite sure how explain that kind of dependency to GNU make.
I've tried listing config/config_file.cfg as a dependency for config_hash.h, and providing a .PHONY target for config_file.cfg without success. Obviously, I can't rely on the -M switch to gcc to help me here, since the config file is not a part of any object code.
Any suggestions? Unfortunately, I can't post much of the Makefile, or I would have just posted the whole thing.
