linux-kernel - Re: [PATCH 6/6] arm64: switch to relative exception tables

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Date:	Mon, 4 Jan 2016 20:28:52 +0100
From:	Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Luck, Tony" <tony.luck@...el.com>,
	Will Deacon <will.deacon@....com>,
	"linux-alpha@...r.kernel.org" <linux-alpha@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
	"linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"heiko.carstens@...ibm.com" <heiko.carstens@...ibm.com>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"mattst88@...il.com" <mattst88@...il.com>,
	"ink@...assic.park.msu.ru" <ink@...assic.park.msu.ru>,
	"rth@...ddle.net" <rth@...ddle.net>,
	"Yu, Fenghua" <fenghua.yu@...el.com>,
	"catalin.marinas@....com" <catalin.marinas@....com>,
	"arnd@...db.de" <arnd@...db.de>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"mark.rutland@....com" <mark.rutland@....com>,
	"marc.zyngier@....com" <marc.zyngier@....com>
Subject: Re: [PATCH 6/6] arm64: switch to relative exception tables

On 4 January 2016 at 20:21, H. Peter Anvin <hpa@...or.com> wrote:
> On 01/04/2016 10:20 AM, Luck, Tony wrote:
>>> May I humbly ask why the [Finnish] you don't use the equivalent of the
>>> x86 _ASM_EXTABLE() macro?  In fact, why don't we make that one generic, too?
>>
>> I'm messing with that right now (with help from Andy Lutomirski and Boris) to
>> add different classes of exception table (so I can tag some instructions as being
>> suitable for fixup from the machine check handler).  So it might not be generic
>> for much longer.
>>
>> http://marc.info/?l=linux-kernel&m=145187079504846&w=2
>>
>
> I suspect that means we will also need to go back to arch-specific
> sorting for x86.
>

AFAICT, Tony's patches are not incompatible with mine. The fixup
address is offset with a large constant, but this does not affect the
sort order (since that is based on the other member), and the swap
operation that adds/subtracts the delta should not care about the
class bits. (I don't see any changes to sort_extable() in Tony's
patch)

@Tony: any comments? And do you have any objections to the ia64 patch
in this series?

I agree that it makes sense to define a macro to emit the extable
entries in this patch, but I am not sure how that extrapolates to the
other architectures, and testing those is going to be cumbersome for
me, so I'd prefer to keep that a local change for arm64 for now.

Thanks,
Ard.
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