Messages in this thread | | | Date | Mon, 3 Jun 2019 13:13:24 -0700 | From | "Paul E. McKenney" <> | Subject | Re: single copy atomicity for double load/stores on 32-bit systems |
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On Mon, Jun 03, 2019 at 06:08:35PM +0000, Vineet Gupta wrote: > On 5/31/19 1:21 AM, Peter Zijlstra wrote: > >> I'm not sure how to interpret "natural alignment" for the case of double > >> load/stores on 32-bit systems where the hardware and ABI allow for 4 byte > >> alignment (ARCv2 LDD/STD, ARM LDRD/STRD ....) > > Natural alignment: !((uintptr_t)ptr % sizeof(*ptr)) > > > > For any u64 type, that would give 8 byte alignment. the problem > > otherwise being that your data spans two lines/pages etc.. > > Sure, but as Paul said, if the software doesn't expect them to be atomic by > default, they could span 2 hardware lines to keep the implementation simpler/sane.
I could imagine 8-byte types being only four-byte aligned on 32-bit systems, but it would be quite a surprise on 64-bit systems.
Thanx, Paul
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