Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756047AbdLOKgI (ORCPT ); Fri, 15 Dec 2017 05:36:08 -0500 Received: from mail-ot0-f195.google.com ([74.125.82.195]:40394 "EHLO mail-ot0-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755018AbdLOKgC (ORCPT ); Fri, 15 Dec 2017 05:36:02 -0500 X-Google-Smtp-Source: ACJfBot6lgEFzwzXbxrNpcuVxu+TiitjHEqjjx4EKnVL57t+MNe4tPa+w2GLKzdYE3hOWqTTeHrC3wuoU9ZgDOnB55s= MIME-Version: 1.0 In-Reply-To: <1513296698.18523.291.camel@codethink.co.uk> References: <20171127193037.8711-1-deepa.kernel@gmail.com> <20171127193037.8711-8-deepa.kernel@gmail.com> <1513296698.18523.291.camel@codethink.co.uk> From: Arnd Bergmann Date: Fri, 15 Dec 2017 11:36:01 +0100 X-Google-Sender-Auth: 0wfQT6zj2opeFuMAuohXmLh3nAE Message-ID: Subject: Re: [Y2038] [PATCH v2 07/10] include: Add new y2038 safe __kernel_timespec To: Ben Hutchings Cc: Deepa Dinamani , Thomas Gleixner , John Stultz , y2038 Mailman List , linux-arch , Linux Kernel Mailing List , Albert ARIBAUD , GNU C Library Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1403 Lines: 34 On Fri, Dec 15, 2017 at 1:11 AM, Ben Hutchings wrote: > On Mon, 2017-11-27 at 11:30 -0800, Deepa Dinamani wrote: >> --- a/include/uapi/linux/time.h >> +++ b/include/uapi/linux/time.h >> @@ -42,6 +42,13 @@ struct itimerval { >> > > struct timeval it_value; /* current value */ >> }; >> >> +#ifndef __kernel_timespec >> +struct __kernel_timespec { >> + __kernel_time64_t tv_sec; /* seconds */ >> + long long tv_nsec; /* nanoseconds */ >> +}; >> +#endif > > I wonder if it makes sense to override the alignment of this structure? > (64-bit types are aligned differently on 32-bit vs 64-bit x86, but not > other compat cases.) It might reduce the need for conversions in > compat code elsewhere later. I think the alignment here should be agreed with glibc so they use the same alignment for their new timespec. I don't see a specific mention of this at https://sourceware.org/glibc/wiki/Y2038ProofnessDesign#struct___timespec64 so I'm adding Albert and libc-alpha to Cc for clarification. I agree it would simplify things a bit to ensure that time64_t and __timespec64/__kernel_timespec have a 64-bit alignment even on x86-32, but I don't know if there is precedent for using gcc __attribute__((aligned(8)) on POSIX data types, of if that might cause problems e.g. for non-gnu compilers. Arnd