Re: [PATCH v3 2/2] feature_test_macros.7: document _TIME_BITS (time64)

[Alejandro Colomar <alx.manpages@gmail.com>]

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On 10/13/22 22:58, Sam James wrote:
> Some notes:
> * glibc is the only libc I'm aware of implementing _TIME_BITS for time64
> compatibility. It was introduced in glibc-2.34;
> 
> * musl libc made a hard switch in 1.2.0, see https://musl.libc.org/time64.html;
> 
> * Using _TIME_BITS=64 with glibc requires _FILE_OFFSET_BITS=64 (which is used
> for Large File Support)! Extraordinary claims require (some) evidence, so see
> https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/features-time64.h;h=84d56ee3ff2ecfa0d2499385623f30606f84a1bf.
> 
> Reference: https://wiki.gentoo.org/wiki/Project:Toolchain/time64_migration
> Reference: https://sourceware.org/pipermail/libc-alpha/2022-January/134985.html
> Signed-off-by: Sam James <sam@gentoo.org>

Patch applied.

Thanks,
Alex

> ---
>   man7/feature_test_macros.7 | 15 +++++++++++++++
>   1 file changed, 15 insertions(+)
> 
> diff --git a/man7/feature_test_macros.7 b/man7/feature_test_macros.7
> index cdd962f7f..bcd6e6ae9 100644
> --- a/man7/feature_test_macros.7
> +++ b/man7/feature_test_macros.7
> @@ -412,6 +412,17 @@ large files with only a recompilation being required.)
>   64-bit systems naturally permit file sizes greater than 2 Gigabytes,
>   and on those systems this macro has no effect.
>   .TP
> +.B _TIME_BITS
> +Defining this macro with the value 64
> +changes the width of
> +.BR time_t (3type)
> +to 64-bit which allows handling of timestamps beyond
> +2038.
> +It is closely related to
> +.B _FILE_OFFSET_BITS
> +and depending on implementation, may require it set.
> +This macro is available as of glibc 2.34.
> +.TP
>   .BR _BSD_SOURCE " (deprecated since glibc 2.20)"
>   Defining this macro with any value causes header files to expose
>   BSD-derived definitions.
> @@ -854,6 +865,10 @@ main(int argc, char *argv[])
>       printf("_FILE_OFFSET_BITS defined: %d\en", _FILE_OFFSET_BITS);
>   #endif
>   
> +#ifdef _TIME_BITS
> +    printf("_TIME_BITS defined: %d\en", _TIME_BITS);
> +#endif
> +
>   #ifdef _BSD_SOURCE
>       printf("_BSD_SOURCE defined\en");
>   #endif

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