linux-kernel - Re: [RFC Patch v1 45/55] ARC: unaligned access emulation

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Date:	Thu, 20 Dec 2012 13:38:43 +0530
From:	Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	<linux-arch@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<tglx@...utronix.de>
Subject: Re: [RFC Patch v1 45/55] ARC: unaligned access emulation

On Monday 12 November 2012 07:30 PM, Arnd Bergmann wrote:
> On Monday 12 November 2012, Vineet.Gupta1@...opsys.com wrote:
>> +
>> +config ARC_MISALIGN_ACCESS
>> +       bool "Emulate unaligned memory access (userspace only)"
>> +       default N
>> +       help
>> +         This enables misaligned 16 & 32 bit memory access from user space.
>> +         Use ONLY-IF-ABS-NECESSARY as it will be very slow and also can hide
>> +         potential bugs in code
> 
> parisc and ia64 both have the same feature, and they use sysctl to configure
> it at run-time. Maybe you should pick one of the two sysctl implementations
> and hook that up to your implementation as well.

Spoke too soon ! The only caveat to removing the Kconfig option is that
it will pull-in unaligned emulation code as well as the dependent
in-kernel disassembler unconditionally into the build.

Are you OK if we keep this support build time - provided that once it is
build time enabled - we have the additional runtime sysctl based
toggle-ability as you suggested.

Only one of our customers need this feature and this gives people
reasons to moan about the kernel .text size and such.

Thanks,
Vineet

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