how do I make a makefile depend on the build options

Question

A long time ago, I remember using some Solaris make, and they had an ingenious option that would automatically detect when the compiler options had changed, and rebuild all rules appropriately. For example, suppose I switch from:

g++ -O3

to

g++ -g

Then all files should be recompiled. I'm using gnu make, and haven't found any feature like this, and was wondering whether anyone has a way of making it work.

Answer 1

A simple way to achieve this with gmake is to write the gcc options into a file. Then, in the Makefile, read these options to a variable, use this variable in the gcc command line, plus add the dependency for all object files to this option file (can be done in the pattern rule).