Re: [PATCH v2 2/7] y2038: Introduce __ASSUME_64BIT_TIME define

[Arnd Bergmann <arnd at arndb dot de>]

On Fri, May 17, 2019 at 9:23 AM Florian Weimer <fweimer@redhat.com> wrote:
>
> * Joseph Myers:
>
> > I'd expect the only effects of allowing for not having __NR_* would
> > generally be that the case where the syscalls are not assumed to be
> > available at runtime also has an #ifdef on the __NR_* macro, so that if
> > it's not defined it falls straight through into exactly the same fallback
> > code as if the syscall had failed with ENOSYS.
>
> An alternative would be to ship all the system call constants in the
> glibc source tree (and check that they match the installed kernel header
> sources if available there).

To clarify: I was not asking about the __NR_* constants, as those don't
ever change, and using older headers will not cause incorrect behavior
but just invoke the fallback.

The two classes of problems I'm interested in are:

- constants that depend on 'sizeof(time_t)', e.g. SO_TIMESTAMP
- structures that used time_t instead of a fixed-length type in older
  headers, e.g. 'struct input_event'

We have a number of those, and in each case, using the old
kernel headers will lead to an ABI mismatch between the application
and the kernel.

       Arnd