linux-kernel - Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT

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Date:   Mon, 30 Dec 2019 15:37:17 +0100
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "open list:BROADCOM NVRAM DRIVER" <linux-mips@...r.kernel.org>,
        Paul Burton <paulburton@...nel.org>,
        Vincenzo Frascino <vincenzo.frascino@....com>,
        Christian Brauner <christian.brauner@...onical.com>
Subject: Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME

On Mon, Dec 30, 2019 at 1:34 PM Arnd Bergmann <arnd@...db.de> wrote:
>
> - Why does it crash in the first place rather than returning -ENOSYS?

There's a bit of speculation about this in the original thread that
prompted this patch (you're CC'd).

>
> - How does it actually work if you run an application built against
>   an old musl version on a kernel that tries to make this not work?
>   Do you just get a random time (uninitialized user space stack) and
>   work with that without checking the error code?

Actually, your patch fails here. The ts struct remains as it was
before, filled with garbage. No good. My original patch in this
thread, though, does result in the correct value being written to ts.

Jason