linux-kernel - Re: [PATCH 1/2] arm64: bpf: add 'store immediate' instruction

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Date:	Thu, 12 Nov 2015 11:33:15 -0800
From:	"Shi, Yang" <yang.shi@...aro.org>
To:	Will Deacon <will.deacon@....com>, Z Lim <zlim.lnx@...il.com>
CC:	Alexei Starovoitov <ast@...nel.org>, daniel@...earbox.net,
	Catalin Marinas <catalin.marinas@....com>,
	Xi Wang <xi.wang@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	linaro-kernel@...ts.linaro.org
Subject: Re: [PATCH 1/2] arm64: bpf: add 'store immediate' instruction

On 11/11/2015 4:39 AM, Will Deacon wrote:
> On Wed, Nov 11, 2015 at 12:12:56PM +0000, Will Deacon wrote:
>> On Tue, Nov 10, 2015 at 06:45:39PM -0800, Z Lim wrote:
>>> On Tue, Nov 10, 2015 at 2:41 PM, Yang Shi <yang.shi@...aro.org> wrote:
>>>> aarch64 doesn't have native store immediate instruction, such operation
>>>
>>> Actually, aarch64 does have "STR (immediate)". For arm64 JIT, we can
>>> consider using it as an optimization.
>>
>> Yes, I'd definitely like to see that in preference to moving via a
>> temporary register.
>
> Wait a second, we're both talking rubbish here :) The STR (immediate)
> form is referring to the addressing mode, whereas this patch wants to
> store an immediate value to memory, which does need moving to a register
> first.

Yes, the immediate means immediate offset for addressing index. Doesn't 
mean to store immediate to memory.

I don't think any load-store architecture has store immediate instruction.

Thanks,
Yang

>
> So the original patch is fine.
>
> Will
>

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