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From:   Arnd Bergmann <arnd@arndb.de>
Date:   Mon, 30 Dec 2019 16:47:37 +0100
Message-ID: <CAK8P3a0NBuqDX63+920q7Q+yO2xCoSd0O7xUDJv6BBoco2kVOg@mail.gmail.com>
Subject: Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME
To:     "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
        Paul Burton <paulburton@kernel.org>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        Christian Brauner <christian.brauner@canonical.com>
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On Mon, Dec 30, 2019 at 4:39 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
>
> On Mon, Dec 30, 2019 at 4:37 PM Arnd Bergmann <arnd@arndb.de> wrote:
> >
> > On Mon, Dec 30, 2019 at 3:37 PM Jason A. Donenfeld <Jason@zx2c4.com> wrote:
> > >
> > > On Mon, Dec 30, 2019 at 1:34 PM Arnd Bergmann <arnd@arndb.de> wrote:

> > Returning success from clock_gettime() on a kernel with only
> > time64 support and a libc with only time32 support (or vice
> > versa) would be a bug.
>
> Ah, right, hence why the 32-bit compat code is behind a
> still-on-by-default-but-not-for-long menu option.

I expect this to remain on-by-default for a rather long time, as we still
to run old binaries well into 2030s. Making it configurable is done for
two reasons:

- on embedded systems that have all user space built with time64,
  turning this off can make the kernel slightly smaller

- turning it off lets you check that no code relies on calling the old
  interfaces internally, bypassing the C library, in a way that works
  at the moment but may break after 2038.

         Arnd