From: Vineet Gupta <Vineet.Gupta1@synopsys.com>
To: David Laight <David.Laight@ACULAB.COM>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <Will.Deacon@arm.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: "linux-arch@vger.kernel.org" <linux-arch@vger.kernel.org>,
arcml <linux-snps-arc@lists.infradead.org>,
lkml <linux-kernel@vger.kernel.org>
Subject: Re: single copy atomicity for double load/stores on 32-bit systems
Date: Mon, 3 Jun 2019 11:44:52 -0700 [thread overview]
Message-ID: <b6dbe51f-88a8-0b18-e0e7-147d8022ad54@synopsys.com> (raw)
In-Reply-To: <895ec12746c246579aed5dd98ace6e38@AcuMS.aculab.com>
On 5/31/19 2:41 AM, David Laight wrote:
>> While it seems reasonable form hardware pov to not implement such atomicity by
>> default it seems there's an additional burden on application writers. They could
>> be happily using a lockless algorithm with just a shared flag between 2 threads
>> w/o need for any explicit synchronization. But upgrade to a new compiler which
>> aggressively "packs" struct rendering long long 32-bit aligned (vs. 64-bit before)
>> causing the code to suddenly stop working. Is the onus on them to declare such
>> memory as c11 atomic or some such.
> A 'new' compiler can't suddenly change the alignment rules for structure elements.
> The alignment rules will be part of the ABI.
>
> More likely is that the structure itself is unexpectedly allocated on
> an 8n+4 boundary due to code changes elsewhere.
Indeed thats what I meant that the layout changed as is typical of a new compiler.
prev parent reply other threads:[~2019-06-03 18:45 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-30 18:22 single copy atomicity for double load/stores on 32-bit systems Vineet Gupta
2019-05-30 18:53 ` Paul E. McKenney
2019-05-30 19:16 ` Vineet Gupta
2019-05-31 8:23 ` Peter Zijlstra
2019-05-31 8:25 ` Peter Zijlstra
2019-05-31 8:21 ` Peter Zijlstra
2019-06-03 18:08 ` Vineet Gupta
2019-06-03 20:13 ` Paul E. McKenney
2019-06-03 21:59 ` Vineet Gupta
2019-06-04 7:41 ` Geert Uytterhoeven
2019-06-06 9:43 ` Paul E. McKenney
2019-06-06 9:53 ` Geert Uytterhoeven
2019-06-06 16:34 ` David Laight
2019-06-06 21:17 ` Paul E. McKenney
2019-06-03 18:43 ` Vineet Gupta
2019-07-01 20:05 ` Vineet Gupta
2019-07-02 10:46 ` Will Deacon
2019-05-31 9:41 ` David Laight
2019-05-31 11:44 ` Paul E. McKenney
2019-06-03 18:44 ` Vineet Gupta [this message]
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