linux-kernel - Re: [RFC] kbuild: generic support for asm-generic

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Date:	Sun, 9 Jan 2011 01:15:58 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Sam Ravnborg <sam@...nborg.org>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	"linux-kbuild" <linux-kbuild@...r.kernel.org>,
	linux arch <linux-arch@...r.kernel.org>,
	Guan Xuetao <guanxuetao@...c.pku.edu.cn>,
	Michal Marek <mmarek@...e.cz>
Subject: Re: [RFC] kbuild: generic support for asm-generic

On Saturday 08 January 2011, Sam Ravnborg wrote:
> We need a variables to express:
> In include/asm-generic/Kbuild.asm
> - This file exists in a generic variant and it is exported.
>   The arch may use it verbatim or may have a local variant

Actually, this is not how we traditionally use Kbuild.asm:
This file is only included from the other asm/Kbuild files to
get the list of common files that should be exported from the
architectures. Originally, this included even files that had
no asm-generic counterpart, but that has probably changed now.

The naming of that file may have been a bit confusing.

We already have the list of exported files in
include/asm-generic/Kbuild that sort of does what you describe.

> In arch/$(ARCH)/include/Kbuild.asm-generic
> - This file is provided verbatim by asm-generic

I would just put this information into the 
arch/$(ARCH)/include/Kbuild file, with a different variable
name.

The other complication is that not all the files that an
architecture may take verbatim from asm-generic are also
exported.

> Something like:
> 
> export-y - for files listed in Kbuild.asm
> generic-y - for files listed in Kbuild.asm-generic
> 
> I will try to come up with a patch that uses this - or something
> similar.

Ok.

Would it be enough to have this?:

"generic-y" in arch/$(ARCH)/include/asm/Kbuild:
  The architecture does not provide this header, the kernel should use
  the asm-generic version through a generated file.

"header-y" in arch/$(ARCH)/include/asm/Kbuild and include/asm-generic/Kbuild.asm:
  This file gets exported to user space (as before), and may come from either
  arch/$(ARCH)/include/asm or include/asm-generic (if listed as generic-y).

"header-y" in include/asm-generic/Kbuild: The asm-generic version of the header
 gets installed. We always do this, because there might be reasons to install
 headers for multiple architectures (with a symlink or similar).

We could either install the generated file or a copy of the asm-generic file
for any exported header that the architecture does not have itself.

	Arnd
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