Hi all.  I'm trying to build an out-of-tree module, which actually has
configuration associated with it (it has a Kconfig file and
everything--although that doesn't help me for out-of-tree builds of

I have my own makefile which invokes the appropriate kbuild-based make
(setting O= etc. on the command line).  I know what configure options I
want to set as well.

So, I wanted to figure out how just pass a couple of -DCONFIG_...=... on
the kbuild make command line such that they would be added to the
compile line of my out-of-tree modules.  Unfortunately I can't use
EXTRA_CFLAGS (easily) because the out-of-tree module Makefile sets some
flags in EXTRA_CFLAGS itself.  All things being equal I'd prefer not to
change the module code, or have to duplicate those flags on my
invocation line.

In normal make, the CPPFLAGS variable contains C preprocessor options
and is included in each compile line automatically.  I can see that
kbuild supports EXTRA_CPPFLAGS and cppflags-y etc. but these seem to
have a different purpose; anyway they don't appear on any normal compile
line.  Is this an oversight?  What are these cppflags variables intended
for?  I'm having a hard time finding where they are used.

I also see that I can set KCPPFLAGS on the command line and that works,
although I get a warning.

Is this (KCPPFLAGS) the intended solution for this type of thing,
warning notwithstanding?

Or is there another, better way to manage this?

BTW, I'm using a relatively old kernel (2.6.31) but I'm interested in
comments even if they apply only to newer kernels.


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