linux-kernel - Re: [PATCH v6 01/19] kernel: Standardize vdso

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Message-ID: <20190610174746.GA13224@merlot.physics.ox.ac.uk>
Date:   Mon, 10 Jun 2019 18:47:46 +0100
From:   Huw Davies <huw@...eweavers.com>
To:     Vincenzo Frascino <vincenzo.frascino@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-mips@...r.kernel.org,
        "open list:KERNEL SELFTEST FRAMEWORK" 
        <linux-kselftest@...r.kernel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Russell King <linux@...linux.org.uk>,
        Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Mark Salyzyn <salyzyn@...roid.com>,
        Peter Collingbourne <pcc@...gle.com>,
        Shuah Khan <shuah@...nel.org>,
        Dmitry Safonov <0x7f454c46@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH v6 01/19] kernel: Standardize vdso_datapage

On Tue, Jun 04, 2019 at 01:05:40PM +0100, Vincenzo Frascino wrote:
> On 31/05/2019 09:16, Arnd Bergmann wrote:
> > On Thu, May 30, 2019 at 4:15 PM Vincenzo Frascino
> > <vincenzo.frascino@....com> wrote:
> > 
> >> + * vdso_data will be accessed by 64 bit and compat code at the same time
> >> + * so we should be careful before modifying this structure.
> >> + */
> >> +struct vdso_data {
> >> +       u32                     seq;
> >> +
> >> +       s32                     clock_mode;
> >> +       u64                     cycle_last;
> >> +       u64                     mask;
> >> +       u32                     mult;
> >> +       u32                     shift;
> >> +
> >> +       struct vdso_timestamp   basetime[VDSO_BASES];
> >> +
> >> +       s32                     tz_minuteswest;
> >> +       s32                     tz_dsttime;
> >> +       u32                     hrtimer_res;
> >> +};
> > 
> > The structure contains four padding bytes at the end, which is
> > something we try to avoid, at least if this ends up being used as
> > an ABI. Maybe add "u32 __unused" at the end?
> > 
> 
> Agreed, I will fix this in v7.

Note that this is also necessary to ensure that CLOCK_MONOTONIC_RAW
works in the 32-bit vDSO on x86_64 kernels.

Huw.