linux-kernel - Re: [PATCH v1 2/7] arm64: introduce interfaces to hotpatch kernel and module code

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Message-ID: <CA+b37P2yQOo8X1jyPC-QxRbJ1EHL7U06hC_26Gn0SnhMhJKCuA@mail.gmail.com>
Date:	Thu, 26 Sep 2013 08:17:45 +0530
From:	Sandeepa Prabhu <sandeepa.prabhu@...aro.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Jiang Liu <liuj97@...il.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Jiang Liu <jiang.liu@...wei.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 2/7] arm64: introduce interfaces to hotpatch kernel and
 module code

On 25 September 2013 20:46, Steven Rostedt <rostedt@...dmis.org> wrote:
> On Wed, 25 Sep 2013 20:12:17 +0530
> Sandeepa Prabhu <sandeepa.prabhu@...aro.org> wrote:
>
>
>> > On aarch64, are instructions always word aligned? If not, it should be
>> > safe for stop machine to modify non word aligned instructions, but this
>> > patch looks like it doesn't allow stop_machine() to do so.
>> Steve,
>>
>> Yes, aarch64 instructions must be word-aligned, else instruction fetch
>> would generate Misaligned PC fault.
>>
>
> Thanks for clarifying, as IIUC, there's ARM architectures that allow
> for 2 and 4 byte instructions.
Yes, ARM 32-bit mode would support both 32-bit and 16-bit alignment
based on ARM or Thumb mode, whereas
AArch64 (in arch/arm64/) is always 32-bit instructions and PC need to
be aligned to 32-bit address.

Thanks,
Sandeepa
>
> -- Steve
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