Re: Override... but not really

[Philip Prindeville]

 Sorry, I sent that off and then realized that a little context might be more 
useful.

I do a lot of cross-compilation, where the platform requires a set of CFLAGS to 
always be present, such as -march=xxx and -isysroot=yyyy ...

The problem is that if you pass these in from the command line as "make -C foobar 
CFLAGS=..." then any CFLAGS that the package tries to build (either in its top-level 
or submake) makefiles gets ignored.

I'm trying to come up with guidelines for writing cross-compilation friendly makefiles, 
but the behavior of "override" not re-exporting itself makes this a little 
tricky.

Looking for some insight.

Thanks.


On 8/9/10 10:00 AM, Philip Prindeville wrote:
>  Is this expected behavior?
>
> $ cat makefile1
> override CFLAGS+=-DB
>
> $(info makefile1: CFLAGS=$(CFLAGS))
>
> all:
>     make -f makefile2
> $ cat makefile2
>
> $(info makefile2: CFLAGS=$(CFLAGS))
>
> override CFLAGS+=-DC
>
> $(info makefile2: CFLAGS=$(CFLAGS))
>
> all:
>     @echo foo
> $ make -f makefile1 CFLAGS=-DA
> makefile1: CFLAGS=-DA -DB
> make -f makefile2
> makefile2: CFLAGS=-DA
> makefile2: CFLAGS=-DA -DC
> foo
> $
>
>
> So why isn't the CFLAGS that gets passed to the submake set to "-DA -DB"?
>
> This is less than intuitive: it's not *really* overriding if it's only 
> semi-persistent.
>
> What's even more confusing is that make apparently keeps two copies...  the one 
> that's in-scope for the current make, and the one that gets re-exported into 
> sub-makes.
>
> I couldn't find in the documentation where this behavior gets called out.
>
> -Philip