Re: 64 bit time_t on riscv32

[Adhemerval Zanella Netto <adhemerval.zanella@linaro.org>]

On 16/01/24 13:22, Florian Weimer wrote:
> * Rich Felker:
> 
>> On Tue, Jan 16, 2024 at 04:46:17PM +0100, Florian Weimer wrote:
>>> * Adhemerval Zanella Netto:
>>>
>>>> My understanding was __USE_TIME_BITS64 would be required only for ABIs
>>>> that actually would multiple time_t sizes and the glibc 64 bit time_t 
>>>> supported was added on this assumption.  However, the design document 
>>>> does state __USE_TIME_BITS64 would be defined even for architectures 
>>>> where is does not require it.  I it was not really caught in development
>>>> because the design creator was not really much involved at the time.
>>>>
>>>> I think it should be feasible to fix it, although backporting it would
>>>> generate a quite large patch.
>>>
>>> It will break applications that use __USE_TIME_BITS64 with glibc's
>>> current semantics centered on time64 redirects (incorrectly, of
>>> course—it's an internal macro).  I think the use in the kernel is
>>> probably easier to address, and it has to be changed for compatibility
>>> with other libcs anyway.
>>
>> If there are applications assuming __USE_TIME_BITS64 implies redirects
>> and doing some hack around that, they really need to be fixed not to
>> do that. It will break on musl with (not yet merged) rv32 port as well
>> as any future 32-bit ports, which won't have any redirects because
>> there is no legacy 32-bit time_t ABI to support.
> 
> That's actually not a problem because __USE_TIME_BITS64 is not defined
> on rv32 et al. (hence the complaint about what the UAPI headers are
> doing).

A possible fix would just check the redirection with 

  if __USE_TIME_BITS64 && __TIMESIZE == 32

The code is already poking an implementation detail, so it can just
continue to mimic what the installed header would do.