RFC: time_t declaration

[Bruno Haible]

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Hi Robert,

> We have a problem with the time_t declaration:  It is declared with a
> different type in FreeBSD than in GNU.  Therefore the kernel is in
> disparity with libc.
>
> If I understood correctly, in his patchset for kfreebsd 4.6 headers Bruno
> Haible renamed time_t to __kernel_time_t (and analogously for structures
> that contain time_t), presumably to avoid conflict with the time_t
> declaration in libc.  So userland programs need to use __kernel_time_t and
> friends when the data is to be analised by the kernel (after a syscall) and
> time_t when the stuff is for libc.
>
> Bruno, could you confirm (if you remember) that this is the situation?

Yes, this is the situation. More precisely, it's about the 64-bit CPU ports
(such as alpha), and the __kernel_time_t is 32-bit, whereas I wanted the
__time_t to be 64-bit.

I made this choice because 32-bit time_t will overflow in 2038. I expect
that 32-bit systems will not be around any more at that time, but 64-bit
systems will. So all systems which use 32-bit time_t on 64-bit platforms
will have to change their time_t type till then. But time_t is part of
the ABI offered by glibc, and changing it would require a change of the
major version number of glibc.

> I'm considering switching to a model in which userland is adapted to use
> the same value as the kernel.  This would save us work in maintaining the
> patchset for kfreebsd5-headers (which, btw, contains breakage because of
> this), but i'm not sure if Glibc could get into trouble by changing the
> userland time_t definition in <bits/types.h>.

Glibc would not be in trouble. But we would be at the moment when
the FreeBSD kernel changes to use a 64-bit time_t as well and we cannot
change time_t in user land and the year 2038 approaches...

Now, a weak point in this argumentation is that the 'alpha' architecture
is already nearly dead and will be dead before 2038. So it would be good
to check what is the status of the other 64-bit ports in FreeBSD 5.3
(AMD64, SPARC64 etc.). Is the 'alpha' architecture the only one with a
32-bit time_t or not? If yes, then we don't need the __kernel_time_t thing
at all. If no, we need it.

Bruno

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