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Diffstat (limited to 'doc/year2038.texi')
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diff --git a/doc/year2038.texi b/doc/year2038.texi index 213fda235f..d98753101e 100644 --- a/doc/year2038.texi +++ b/doc/year2038.texi @@ -1,25 +1,43 @@ @node Avoiding the year 2038 problem @section Avoiding the year 2038 problem -The ``year 2038 problem'' denotes unpredictable behaviour of programs -that will likely occur in the year 2038, for programs that use a 32-bit -@samp{time_t} type. See @url{https://en.wikipedia.org/wiki/Year_2038_problem} -for details. +The ``year 2038 problem'' denotes unpredictable behaviour that will +likely occur in the year 2038, for programs that use a 32-bit signed +integer @samp{time_t} type that cannot represent timestamps on or +after 2038-01-19 03:14:08 UTC@. See +@url{https://en.wikipedia.org/wiki/Year_2038_problem, Year 2038 +problem} for details. -The Gnulib module @samp{year2038} attempts to avoid this problem, by -ensuring that @code{time_t} is a 64-bit type and by causing -@code{configure} to fail otherwise. +The Gnulib module @samp{year2038-required} fixes this problem, by +making @code{time_t} wide enough to represent timestamps after 2038. +This has no effect on most current systems, which have timestamps that +are already wide enough. However, @samp{year2038-required} arranges +for builds on legacy 32-bit x86 and ARM Linux kernels running glibc +2.34 and later to compile with @samp{_TIME_BITS=64} to get wider +timestamps. On older platforms that do not support timestamps after +the year 2038, @samp{year2038-required} causes @command{configure} to +fail. -The Gnulib module @samp{largefile} also attempts to avoid this problem -when possible, because @samp{largefile} enables the widest -file-related types supported by the system and @code{time_t} is one of -those types. However, @code{largefile} does not cause -@code{configure} to fail when the year 2038 problem is not avoidable. +The Gnulib module @samp{year2038} is like @samp{year2038-required}, +except that it causes @command{configure} to fail only when it appears +that the current system should support post-2038 timestamps but +something prevents that from working. Also, @samp{year2038} gives +@command{configure} a @option{--disable-year2038} option, which +suppresses support for post-2038 timestamps. This may be useful if +the package links to other libraries whose user-facing ABIs still +require @code{time_t} to be 32-bit on your platform. -The Gnulib @samp{largefile} and @samp{year2038} modules are +The Gnulib module @samp{year2038-required} is recommended for any package that might be used after the year 2038 on -32-bit platforms. However, if you build such a package you can -disable its use of 64-bit @code{time_t} by giving the -@code{--disable-year2038} option to @code{configure}. This may be -useful if the package links to other libraries whose user-facing ABIs -still require @code{time_t} to be 32-bit on your platform. +32-bit platforms. However, if your package needs to support +platforms that will not be used after the year 2038, +you can use the @samp{year2038} module instead. + +If the Gnulib module @samp{largefile} is used but neither +@samp{year2038} nor @samp{year2038-required} is used, +@command{configure} will have an option @option{--enable-year2038} +that causes @code{configure} to behave as if @samp{year2038} was used. +This is for packages that have long used @samp{largefile} but have not +gotten around to upgrade their Gnulib module list to include +@samp{year2038-required} or @samp{year2038}. +@xref{Large File Support}. |