linux-kernel - Re: [PATCH 1/3] arch/um/Makefile: remove dead code

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Date:	Fri, 5 Jul 2013 13:23:52 +0100
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Ramkumar Ramachandra <artagnon@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Richard Weinberger <richard@....at>,
	Jeff Dike <jdike@...toit.com>
Subject: Re: [PATCH 1/3] arch/um/Makefile: remove dead code

On Fri, Jul 05, 2013 at 04:12:30PM +0530, Ramkumar Ramachandra wrote:
> Al Viro wrote:
> > [...]
> > IOW, any make variable (== macro in POSIX quote above) can be explicitly
> > set in make(1) command line in form name=value and in that case nothing in
> > makefile(s) can change its value.  It's true for GNU make, it's true for
> > BSD make and it's been true for historical Unix make since its introduction
> > in v7.
> 
> Thanks Al, the education is much appreciated.  I always thought =
> would override it, and ?= was for default value.

?= is a different story - it refuses to override _any_ earlier declarations,
including ones in makefile itself.  GNU make has added it fairly late, BTW -
in 3.77 (1998); BSD make has grown it at some point during the rewrite
Adam de Boor had been doing in late 80s.  NFI whether he'd invented it or
picked it elsewhere - there had been a lot of cross-pollination between the
variants of make(1) all along...
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