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Subject: Re: MIPS: bug: gettimeofday syscall broken on CI20 board
From:   "H. Nikolaus Schaller" <hns@goldelico.com>
In-Reply-To: <dbf536da-77a6-30a0-a380-9463f604d1a8@arm.com>
Date:   Thu, 28 Nov 2019 13:11:35 +0100
Cc:     Ralf Baechle <ralf@linux-mips.org>,
        Paul Burton <paul.burton@mips.com>, linux-mips@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        MIPS Creator CI20 Development 
        <mips-creator-ci20-dev@googlegroups.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@openphoenux.org>
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References: <18788C50-F29B-4BD7-89F6-B056FF490214@goldelico.com> <703DC004-96E8-463D-8870-3CC410FE1C5E@goldelico.com> <3190d1a4-96c4-1843-3ae1-bae3a97af9fb@arm.com> <8D151C34-41A1-4DFE-92D6-D1B27AEC8730@goldelico.com> <dbf536da-77a6-30a0-a380-9463f604d1a8@arm.com>
To:     Vincenzo Frascino <vincenzo.frascino@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
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> Am 28.11.2019 um 12:51 schrieb Vincenzo Frascino =
<vincenzo.frascino@arm.com>:
>=20
> Hi Nikolaus,
>=20
> On 27/11/2019 13:53, H. Nikolaus Schaller wrote:
> [...]
>=20
>>> vdso_data and mips_vdso_data before are not part of the ABI hence =
they are not
>>> bind by a contract with the userspace.
>>>=20
>>> This means that they can change at any point and if a userspace =
software relies
>>> on a specific layout of these data structures is doing something =
wrong.
>>=20
>> Maybe the libs are clever enough to find that out dynamically but I =
have no
>> idea about how gettimeofday() and user-space VDSO is implemented to =
handle such
>> changes.
>>=20
> As I said userspace applications and libraries should not rely on the =
layout of
> vdso_data because this is not part of the ABI.
>=20
> The only thing that userspace requires is to "know" that =
gettimeofday() exists,
> than it is gettimeofday() that internally accesses the data structure.

Well, with user-space I include the lib that provides the gettimeofday() =
syscall
and reads out the memory region where the VDSO data structure is =
provided by the
kernel. And that part comes from Debian. Somehow it does differently =
with 4.19
than 5.4. So I summarise all non-kernel code with the term "user-space".

BR,
Nikolaus