Re: [PATCH] linux: Use 'long int' for timespec tv_nsec on x32 (BZ #16437)

[Florian Weimer <fweimer@redhat.com>]

* Arnd Bergmann:

> On Fri, Dec 10, 2021 at 12:29 PM Florian Weimer <fweimer@redhat.com> wrote:
>> > On Thu, Dec 9, 2021 at 8:35 PM Adhemerval Zanella via Libc-alpha
>> > <libc-alpha@sourceware.org> wrote:
>> >> On 09/12/2021 16:19, Florian Weimer wrote: * Adhemerval Zanella via Libc-alpha:
>> >
>> >> > The change is also not entirely ABI-compatible because existing code on
>> >> > x32 depends on the implementation clearing the upper 32 bits, and if new
>> >> > code copies around structs, it won't necessary copy the zero bits.
>> >>
>> >> Afaiu the high-bits clearing is strictly necessary on kABI boundary for
>> >> set functions.  Some issues indeed might arise if user use timespec
>> >> embedded in some function and mix objects built with different glibc
>> >> version, but it is similar to 32-bit architectures with mixing time_t
>> >> objects.
>> >
>> > The kernel's 32-bit ABI ignores the upper 32 bits of tv_nsec for structures
>> > passed from user space, but zeroes them when returning a timespec to user
>> > space.
>>
>> And that zeroing may get lost if the struct has padding.  That's my
>> concern.
>
> Which struct? I am talking about __kernel_timespec, which has
> no padding on any architecture, and this is what gets used in the uabi
> headers.

The proposed new glibc struct timespec for x32.

Thanks,
Florian