linux-kernel - Re: [Y2038] [PATCH 5/9] y2038: introduce CONFIG_64BIT

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Date:   Fri, 8 Dec 2017 09:01:50 -0800
From:   Deepa Dinamani <deepa.kernel@...il.com>
To:     Ben Hutchings <ben.hutchings@...ethink.co.uk>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        John Stultz <john.stultz@...aro.org>,
        y2038 Mailman List <y2038@...ts.linaro.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>
Subject: Re: [Y2038] [PATCH 5/9] y2038: introduce CONFIG_64BIT_TIME

On Fri, Dec 8, 2017 at 8:53 AM, Ben Hutchings
<ben.hutchings@...ethink.co.uk> wrote:
> On Fri, 2017-11-10 at 14:42 -0800, Deepa Dinamani wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>>
>> There are a total of 53 system calls (aside from ioctl) that pass a time_t
>> or derived data structure as an argument, and in order to extend time_t
>> to 64-bit, we have to replace them with new system calls and keep providing
>> backwards compatibility.
>>
>> To avoid adding completely new and untested code for this purpose, we
>> introduce a new CONFIG_64BIT_TIME symbol. Every architecture that supports
>> new 64 bit time_t syscalls enables this config via ARCH_HAS_64BIT_TIME.
>>
>> After this is done for all architectures, the CONFIG_64BIT_TIME symbol
>> can be made a user-selected option, to enable users to build a kernel
>> that only provides y2038-safe system calls by making 32 time_t syscalls
>> conditionally included based on the above config.
>
> I don't understand why we would want to change the semantics of
> CONFIG_64BIT_TIME symbol from "enable 64-bit time support" to "disable
> 32-bit time support".
>
> Why not add two config symbols:
>
> config 32BIT_TIME
>         def_bool COMPAT || !64BIT
>
> config 64BIT_TIME
>         def_bool ARCH_HAS_64BIT_TIME
>
> and then make 32BIT_TIME user-configurable later?

This was already discussed on the review and we have an updated version:

https://lkml.org/lkml/2017/11/27/938

>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>> Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
>> ---
>>  arch/Kconfig | 11 +++++++++++
>>  1 file changed, 11 insertions(+)
>>
>> diff --git a/arch/Kconfig b/arch/Kconfig
>> index 8911ff37335a..3266ac1a4ff7 100644
>> --- a/arch/Kconfig
>> +++ b/arch/Kconfig
>> @@ -875,6 +875,17 @@ config OLD_SIGACTION
>>  config COMPAT_OLD_SIGACTION
>>       bool
>>
>> +config ARCH_HAS_64BIT_TIME
>> +     def_bool n
>> +
>> +config CONFIG_64BIT_TIME
>
> The CONFIG_ prefix is added by kconfig scripts and shouldn't be used in
> the Kconfig file.

Yes, this was a typo and was fixed by the next revision which has
already been posted:

https://lkml.org/lkml/2017/11/27/938

-Deepa