Re: [PATCH] mips: vdso: conditionalize 32-bit time functions on COMPAT_32BIT_TIME

[Arnd Bergmann]

On Mon, Dec 30, 2019 at 3:37 PM Jason A. Donenfeld <Jason@xxxxxxxxx> wrote:
>
> On Mon, Dec 30, 2019 at 1:34 PM Arnd Bergmann <arnd@xxxxxxxx> 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.

Ok, that is the intended behavior then, clock_gettime() needs
to fail with -EINVAL or -ENOSYS here (depending on the libc
implementation), and of course the data is not updated.

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.

    Arnd