Re: Problems with recompiling, when changing header files in C

[Paul D. Smith]

%% Peter Biechele <address@hidden> writes:

  pb> I create dependencies using .d files automatically uisng the gcc -M 
feature
  pb> I include the so created .d files using:
  pb>   -include $(C_SRC_FILES:.c=.d)
  pb>   -include $(ASS_SRC_FILES:.ss=.d)

I assume that in your makefile you're not really prefixing these lines
with a TAB, as you've done here, are you?

That would be Very Bad.

  pb> Then if I change one of the c files everything works great. 
  pb> BUT if I change one of the header files, nothing gets recompiled !!!!!

  pb> One of the .d files looks for example like this:
  pb> - -------------------
  pb> modTask.o modTask.d : aufsicht/modTask.c \
  pb>  include/hwdefs.h 
  pb> - -------------------
  pb> If I change the file include/hwdefs.h, NOTHING gets recompiled !!!!

  pb> I use rules like:
  pb> - ----------------
  pb> ## Rules to make the object files
  pb> ##
  pb> %.o : %.c $(ALL_MAKEFILES) 
  pb>   @echo " **** Compiling file $< "
  pb>   $(CC) -c $(CFLAGS) $< -o $(OBJECT_DIR)/$(notdir $@)

  pb> %.o : %.ss $(ALL_MAKEFILES)
  pb>   @echo " **** Compiling file $< "
  pb>   $(CC) -c $(CFLAGS) $< -o $(OBJECT_DIR)/$(notdir $@)
  pb> - -----------------------

You don't show the line that references the .o's, but I bet it's
something like:

  foo: $(patsubst %.c,$(OBJECT_DIR)/%.o,$(C_SRC_FILES))

Your problem is that you're breaking Paul's Second Rule of Makefiles
with your implicit %.o rules above.  You _cannot_ use this method to put
object files in remote directories and have it work correctly.

This rule:

 %.o : %.c $(ALL_MAKEFILES) 
        @echo " **** Compiling file $< "
        $(CC) -c $(CFLAGS) $< -o $(OBJECT_DIR)/$(notdir $@)

tells make that if it runs the script you gave, it will create a file
XXX.o from a file XXX.c... but that's _NOT_ what the rule does; it
creates a file $(OBJECT_DIR)/XXX.o.  You've lied to make, and it will
have its revenge! :).

Check my site below for some docs on this.

-- 
-------------------------------------------------------------------------------
 Paul D. Smith <address@hidden>          Find some GNU make tips at:
 http://www.gnu.org                      http://www.paulandlesley.org/gmake/
 "Please remain calm...I may be mad, but I am a professional." --Mad Scientist