linux-kernel - Re: single copy atomicity for double load/stores on 32-bit systems

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Message-ID: <77b30ed2-3211-222b-1342-051a6cde4f77@synopsys.com>
Date:   Mon, 3 Jun 2019 11:43:20 -0700
From:   Vineet Gupta <Vineet.Gupta1@...opsys.com>
To:     Peter Zijlstra <peterz@...radead.org>
CC:     Will Deacon <Will.Deacon@....com>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        arcml <linux-snps-arc@...ts.infradead.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: single copy atomicity for double load/stores on 32-bit systems

On 5/31/19 1:21 AM, Peter Zijlstra wrote:
> And I'll stand by my earlier conviction that any architecture that has a
> native u64 (be it a 64bit arch or a 32bit with double-width
> instructions) but has an ABI that allows u32 alignment on them is daft.

Why ? For 64-bit data on 32-bit systems, hardware doesn't claim to provide any
single-copy atomicity for such data and software doesn't expect either.