Re: Creating an advanced build system

[John Graham-Cumming]

On Thu, 2005-05-26 at 21:44 +0100, Brendan Heading wrote:
> That was interesting, your proposal is to avoid recursion by including 
> the makefiles. Unfortunately I suspect there'll be trouble if the 
> included Makefiles happen to redefine variables. For example it might be 
> useful for two different libraries to be compiled with different CFLAGS; 
> how would you handle that ?

(I copied the mailing list on this reply because the answer may be
useful to others).

So that's probably the #1 objection to non-recursive Make, but I think
it's fairly simple to handle using GNU Make's pattern-specific
variables.

If you look at how I define special rules to put the output in the right
place for each module:

$($(X_MODULE)_OUTPUT)/%.o: $(X_MODULE)/%.c
        @$(COMPILE.c) -o '$@' '$<'
$($(X_MODULE)_OUTPUT)/$(BINARY).a: $($(X_MODULE)_OBJS)
        @$(AR) r '$@' $^
        @ranlib '$@'
$($(X_MODULE)_OUTPUT)/$(BINARY)$(X_EXEEXT): $($(X_MODULE)_OBJS)
        @$(LINK.cpp) $^ -o'$@'

Then it's pretty easy to give a specific CFLAGS for the creation of .o's
in a specific module because the module is encoded in the full path of
the .o.

For example, suppose that you want CFLAGS to have the -W option set just
for the library and not the executable.  All you need to do is add

$($(X_MODULE)_OUTPUT)/%.o: CFLAGS += -W

To the Makefile in the library/ directory.  Running an -n on this shows
the effect (I made X_OUTTOP be /tmp):

cc -W   -c -o '/tmp/Linux_i686/library/lib1.o' 'library/lib1.c'
cc -W   -c -o '/tmp/Linux_i686/library/lib2.o' 'library/lib2.c'
ar r
'/tmp/Linux_i686/library/lib.a' /tmp/Linux_i686/library/lib1.o 
/tmp/Linux_i686/library/lib2.oranlib '/tmp/Linux_i686/library/lib.a'
cc    -c -o '/tmp/Linux_i686/executable/foo.o' 'executable/foo.c'
cc    -c -o '/tmp/Linux_i686/executable/bar.o' 'executable/bar.c'
g+
+     /tmp/Linux_i686/executable/foo.o /tmp/Linux_i686/executable/bar.o 
/tmp/Linux_i686/library/lib.a -o'/tmp/Linux_i686/executable/exec'

Now suppose that you want the exectuable to be built with -g in CFLAGS.
Just add 

$($(X_MODULE)_OUTPUT)/%.o: CFLAGS += -g

to the executable/ Makefile and now the output looks like this:

cc -W   -c -o '/tmp/Linux_i686/library/lib1.o' 'library/lib1.c'
cc -W   -c -o '/tmp/Linux_i686/library/lib2.o' 'library/lib2.c'
ar r
'/tmp/Linux_i686/library/lib.a' /tmp/Linux_i686/library/lib1.o 
/tmp/Linux_i686/library/lib2.oranlib '/tmp/Linux_i686/library/lib.a'
cc -g   -c -o '/tmp/Linux_i686/executable/foo.o' 'executable/foo.c'
cc -g   -c -o '/tmp/Linux_i686/executable/bar.o' 'executable/bar.c'
g+
+     /tmp/Linux_i686/executable/foo.o /tmp/Linux_i686/executable/bar.o 
/tmp/Linux_i686/library/lib.a -o'/tmp/Linux_i686/executable/exec'

So the two definitions of CFLAGS are independent of each other.

John.
-- 
John Graham-Cumming

Home: http://www.jgc.org/
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