linux-kernel - Re: linker tables on powerpc

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Date:	Wed, 03 Aug 2016 21:40:17 +1000
From:	Michael Ellerman <mpe@...erman.id.au>
To:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	Fengguang Wu <fengguang.wu@...el.com>,
	Guenter Roeck <linux@...ck-us.net>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: linker tables on powerpc - build issues

"Luis R. Rodriguez" <mcgrof@...not-panic.com> writes:

> I've run into a few compilation issues with linker tables support [0]
> [1] on only a few architectures:
>
> blackfin - compiler issue it seems, I have a work around now in place
> arm  - some alignment issue - still need to iron this out
> powerpc - issue with including <asm/sections.h> on <asm/jump_labels.h>
>
> The issue with powerpc can be replicated easily with the patch below,
> and compilation fails even on a 'make defconfig' configuration, the
> issues are recurring include header ordering issues. I've given this
> some tries to fix but am still a bit bewildered how to best do this
> without affecting non-powerpc compilations.  The patch below
> replicates the changes in question, it does not include the linker
> table work at all, it just includes <asm/sections.h> instead of
> <asm/tables.h> to reduce and provide an example of the issues
> observed. The list of errors are also pretty endless... so was hoping
> some power folks might be able to take a glance if possible. If you
> have any ideas, please let me know.

What is the end goal?

You want to be able to include asm/sections.h in asm/jump_labels.h? So
that you can get some macros to wrap the pushsection etc, am I right?

The biggest problem I see is dereference_function_descriptor(), which
uses probe_kernel(), which pulls in uaccess.h.

But it doesn't really make sense for dereference_function_descriptor()
to be in sections.h AFAICS.

I'll see if I can unstitch it tomorrow.

cheers