linux-kernel - Re: [PATCH v6 1/4] x86: Clean up extable entry format (and free up a bit)

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Date:	Mon, 4 Jan 2016 15:11:08 -0800
From:	Tony Luck <tony.luck@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...nel.org>,
	Dan Williams <dan.j.williams@...el.com>,
	Robert <elliott@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	linux-nvdimm <linux-nvdimm@...1.01.org>, X86-ML <x86@...nel.org>
Subject: Re: [PATCH v6 1/4] x86: Clean up extable entry format (and free up a bit)

On Mon, Jan 4, 2016 at 10:08 AM, Andy Lutomirski <luto@...capital.net> wrote:
> On Mon, Jan 4, 2016 at 9:26 AM, Tony Luck <tony.luck@...il.com> wrote:
>> On Mon, Jan 4, 2016 at 4:07 AM, Borislav Petkov <bp@...en8.de> wrote:

>>> Why not simply:
>>>
>>>         .long (to) - . + (bias) ;
>>>
>>> and
>>>
>>>         " .long (" #to ") - . + "(" #bias ") "\n"
>>>
>>> below and get rid of that _EXPAND_EXTABLE_BIAS()?
>>
>> Andy - this part is your code and I'm not sure what the trick is here.
>
> I don't remember.  I think it was just some preprocessor crud to force
> all the macros to expand fully before the assembler sees it.  If it
> builds without it, feel free to delete it.

The trick is definitely needed in the case of

# define _EXPAND_EXTABLE_BIAS(x) #x

Trying to expand it inline and get rid of the macro led to
horrible failure. The __ASSEMBLY__ case where the
macro does nothing isn't required ... but does provide
a certain amount of symmetry when looking at the two
versions of _ASM_EXTABLE_CLASS

-Tony
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