linux-kernel - Re: MIPS: bug: gettimeofday syscall broken on CI20 board

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Date:   Thu, 28 Nov 2019 12:21:04 +0000
From:   Vincenzo Frascino <vincenzo.frascino@....com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        Paul Burton <paul.burton@...s.com>, linux-mips@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        MIPS Creator CI20 Development 
        <mips-creator-ci20-dev@...glegroups.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: MIPS: bug: gettimeofday syscall broken on CI20 board

On 28/11/2019 12:11, H. Nikolaus Schaller wrote:
> 
>> Am 28.11.2019 um 12:51 schrieb Vincenzo Frascino <vincenzo.frascino@....com>:
>>
>> Hi Nikolaus,
>>
>> On 27/11/2019 13:53, H. Nikolaus Schaller wrote:
>> [...]
>>
>>>> vdso_data and mips_vdso_data before are not part of the ABI hence they are not
>>>> bind by a contract with the userspace.
>>>>
>>>> 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.
>>>
>>> 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.
>>>
>> As I said userspace applications and libraries should not rely on the layout of
>> vdso_data because this is not part of the ABI.
>>
>> 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".
> 

The the lib that provides the gettimeofday() changes accordingly with vdso_data.
5.4 and 4.19 have 2 different vdso libraries as well.

> BR,
> Nikolaus
> 

-- 
Regards,
Vincenzo

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