linux-kernel - Re: [PATCH 2/2] Enable 'make CONFIG

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Date:	Thu, 11 Aug 2011 00:16:49 +0100
From:	David Woodhouse <dwmw2@...radead.org>
To:	Arnaud Lacombe <lacombar@...il.com>
Cc:	Michal Marek <mmarek@...e.cz>, "H. Peter Anvin" <hpa@...or.com>,
	linux-kernel@...r.kernel.org, linux-kbuild@...r.kernel.org
Subject: Re: [PATCH 2/2] Enable 'make CONFIG_FOO=y oldconfig'

On Wed, 2011-08-10 at 18:33 -0400, Arnaud Lacombe wrote:
> > We're not enabling anything that we're later going to break. I can't see
> > many people *depending* on the fact that 'make CONFIG_SATA_MV=y
> > oldconfig' actually does *nothing* in some cases.
> >
> you are wrong, you ends up with half-baked compile-time dependency,
> which break the build:

s/*nothing*/nothing useful/, for crying out loud.

The point remains that we're not enabling anything which we're later
going to break. Nobody is going to come to *depend* on this behaviour.

And anyway, this behaviour exists even *before* my patches, as Michal
pointed out in a far more helpful and constructive fashion in 
<CACqU3MU4wJb3ij6skod-ZiM+Q0OMTXNdbJ+qWjJW8VZNEP+x1g@...l.gmail.com>
earlier today.

It's simple enough to fix, too:

diff --git a/Makefile b/Makefile
index 1fc5172..6cc7f7b 100644
--- a/Makefile
+++ b/Makefile
@@ -474,6 +474,9 @@ ifeq ($(KBUILD_EXTMOD),)
         endif
 endif
 
+# This could probably be simpler?
+CONFIG_OVERRIDES := $(patsubst line:%,%,$(filter line:%,$(foreach var, $(filter CONFIG_%,$(.VARIABLES)), $(origin $(var)):$(var))))
+
 ifeq ($(mixed-targets),1)
 # ===========================================================================
 # We're called with mixed targets (*config and build targets).
@@ -507,6 +510,10 @@ else
 # Build targets only - this includes vmlinux, arch specific targets, clean
 # targets and others. In general all targets except *config targets.
 
+ifneq ($(CONFIG_OVERRIDES),)
+$(error Cannot perform build targets with CONFIG symbols overridden)
+endif
+
 ifeq ($(KBUILD_EXTMOD),)
 # Additional helpers built in scripts/
 # Carefully list dependencies so we do not try to build scripts twice


-- 
dwmw2

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