Re: Make behaviour changes with new kernel?

[Sam Ravnborg]

On Sat, Aug 15, 2009 at 05:17:23PM -0700, julvr wrote:
> 
> OK, after some more investigation, it looks like this boils down to whether
> EXTRA_CFLAGS is recursivly expanded or simply expanded...  But again, I'm a
> bit out of my depth in this:  In the kernel, there are several places where
> you see
> 
> EXTRA_CFLAGS = xxx
> 
> and others where you see
> 
> EXTRA_CFLAGS := xxxx
> 
> (usb/storage/Makefile and fs/ntfs/Makefile for example)and then a whole lot
> of += modifiers...   So if you have both of these in your make-path, which
> one takes precedence?

In the kernel we handle directories individually.
And we have in a file that is seen by make _before_ your Makefile the following:

    EXTRA_CFLAGS :=

So if you do "+=" then make see this as a simple assignment.

> julvr wrote:
> > 
> > I am trying to compile a driver for the latest linux kernel, and I ran
> > into a difference on how the old and new kernels run sub-makefiles, and
> > I'm curious as to why.  I have a makefile similar to the following:
> > 
> > 
> > include submakfile
> > VAR1 += somevalue

Looks like you try to do something that is more complex than what any of
the in-kernel users do.
In other words - consider if you can simplify this.

Sometimes the best choise is to split it up so you have a clean 2.6
Makefile (name it Kbuild and kbuild will pick it up automagically).

        Sam