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Merge "Expand a little on the time_t situation." am: 071d071646

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Change-Id: Ie8ad22c1ba0d0cd406d083894ad9f1a4ef620ccf
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Treehugger Robot 2020-05-20 00:45:45 +00:00 committed by Automerger Merge Worker
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docs/32-bit-abi.md
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@ -81,13 +81,23 @@ For source compatibility, the names containing `64` are also available
in the 64-bit ABI even though they're identical to the non-`64` names.
## `time_t` is 32-bit
## `time_t` is 32-bit on LP32 (y2038)
On 32-bit Android, `time_t` is 32-bit. The header `<time64.h>` and type
`time64_t` exist as a workaround, but the kernel interfaces exposed on 32-bit
Android all use the 32-bit `time_t`.
On 32-bit Android, `time_t` is 32-bit, which will overflow in 2038.
In the 64-bit ABI, `time_t` is 64-bit.
In the 64-bit ABI, `time_t` is 64-bit, which will not overflow until
long after the death of the star around which we currently circle.
The header `<time64.h>` and type `time64_t` exist as a workaround,
but the kernel interfaces exposed on 32-bit Android all use the 32-bit
`time_t` and `struct timespec`/`struct timeval`. Linux 5.x kernels
do offer extra interfaces so that 32-bit processes can pass 64-bit
times to/from the kernel, but we do not plan on adding support for
these to the C library. Convenient use of the new calls would require
an equivalent to `_FILE_OFFSET_BITS=64`, which we wouldn't be able
to globally flip for reasons similar to `_FILE_OFFSET_BITS`, mentioned
above. All apps are already required to offer 64-bit variants, and we
expect 64-bit-only devices within the next few years.
## `pthread_mutex_t` is too small for large pids