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Re: [PATCH v3 00/57] tcg: Improve atomicity support

From: Richard Henderson
Subject: Re: [PATCH v3 00/57] tcg: Improve atomicity support
Date: Tue, 2 May 2023 20:19:38 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.10.0

On 5/2/23 17:11, Peter Maydell wrote:
On Tue, 25 Apr 2023 at 20:32, Richard Henderson
<richard.henderson@linaro.org> wrote:


Based-on: 20230424054105.1579315-1-richard.henderson@linaro.org
("[PATCH v3 00/57] tcg: Simplify calls to load/store helpers")

The main objective here is to support Arm FEAT_LSE2, which says that any
single memory access that does not cross a 16-byte boundary is atomic.
This is the MO_ATOM_WITHIN16 control.

While I'm touching all of this, a secondary objective is to handle the
atomicity of the IBM machines.  Both Power and s390x treat misaligned
accesses as atomic on the lsb of the pointer.  For instance, an 8-byte
access at ptr % 8 == 4 will appear as two atomic 4-byte accesses, and
ptr % 4 == 2 will appear as four 3-byte accesses.

I hope you mean "four 2-byte accesses", although I'm never
quite sure how odd s390x can get :-)

Heh.  Yes, of course.


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