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

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Date:   Thu, 28 Nov 2019 11:51:50 +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

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.

-- 
Regards,
Vincenzo

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