docs: remove outdated section on custom toolchain for 64-bit time_t

Co-authored-by: Ivan Grokhotkov <ivan@espressif.com>

docs/en/api-reference/system/system_time.rst

@@ -142,19 +142,21 @@ To set the local timezone, use the following POSIX functions:
 Once these steps are completed, call the standard C library function ``localtime()``, and it will return the correct local time taking into account the timezone offset and daylight saving time.
 
 
-64-bit ``time_t``
------------------
+Year 2036 and 2038 Overflow Issues
+----------------------------------
 
-ESP-IDF uses 32-bit ``time_t`` type by default. To address the Y2K38 issue, you may need to use 64-bit ``time_t`` type when building the application.
+SNTP/NTP 2036 Overflow
+^^^^^^^^^^^^^^^^^^^^^^
 
-Currently, this requires building the cross-compiler toolchain from scratch. See the instructions for building the toolchain in :doc:`/get-started/linux-macos-setup`. To enable 64-bit ``time_t`` support in the toolchain, you need to remove the ``--enable-newlib-long-time_t`` option from the ``crosstool-NG/samples/xtensa-esp32-elf/crosstool.config`` file before building the toolchain.
+SNTP/NTP timestamps are represented as 64-bit unsigned fixed point numbers, where the first 32 bits represent the integer part, and the last 32 bits represent the fractional part. The 64-bit unsigned fixed point number represents the number of seconds since 00:00 on 1st of January 1900, thus SNTP/NTP times will overflow in the year 2036.
 
-If you need to make the program compatible with both 32-bit and 64-bit ``time_t``, you may use the following methods:
+To address this issue, lifetime of the SNTP/NTP timestamps has been extended by convention by using the MSB (bit 0 by convention) of the integer part to indicate time ranges between years 1968 to 2104 (see `RFC2030 <https://www.rfc-editor.org/rfc/rfc2030>`_ for more details). This convention is implemented in lwIP library SNTP module. Therefore SNTP-related functions in ESP-IDF are future-proof until year 2104.
 
-- In C or C++ source files, ``_USE_LONG_TIME_T`` preprocessor macro will be defined if 32-bit ``time_t`` is used. You need to include ``<sys/types.h>`` to make this macro available.
-- In CMake files, ``TIME_T_SIZE`` IDF build property will be set to the size of ``time_t`` in bytes. You may call ``idf_build_get_property(var TIME_T_SIZE)`` to get the value of this property into a CMake variable ``var``. See :ref:`ESP-IDF CMake Build System API <cmake_buildsystem_api>` for more information about ``idf_build_get_property``.
 
-Note that the size of ``time_t`` type also affects the sizes of other types, for example, ``struct timeval``, ``struct stat``, and ``struct utimbuf``.
+Unix Time 2038 Overflow
+^^^^^^^^^^^^^^^^^^^^^^^
+
+Unix time (type ``time_t``) was previously represented as a 32-bit signed integer, leading to an overflow in year 2038 (i.e., `Y2K38 issue <https://en.wikipedia.org/wiki/Year_2038_problem>`_). To address the Y2K38 issue, ESP-IDF uses a 64-bit signed integer to represent ``time_t`` starting from release v5.0, thus deferring ``time_t`` overflow for another 292 billion years.
 
 
 API Reference

docs/zh_CN/api-reference/system/system_time.rst

@@ -142,19 +142,21 @@ lwIP SNTP 库提供了 API 函数，用于设置某个事件的回调函数。
 完成上述步骤后，请调用标准 C 库函数 ``localtime()``。该函数将返回排除时区偏差和夏令时干扰后的准确本地时间。
 
 
-64 位 ``time_t``
------------------
+2036 年和 2038 年溢出问题
+--------------------------------
+
+SNTP/NTP 2036 年溢出问题
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-ESP-IDF 默认使用 32 位的 ``time_t`` 类型。为解决 Y2K38 漏洞，您在构建应用程序时可能需要使用 64 位的 ``time_t`` 类型。
+SNTP/NTP 时间戳为 64 位无符号定点数，其中前 32 位表示整数部分，后 32 位表示小数部分。该 64 位无符号定点数代表从 1900 年 1 月 1 日 00:00 起经过的秒数，因此 SNTP/NTP 时间将在 2036 年溢出。
 
-目前，完成这一操作需要从头开始构建交叉编译器工具链，具体步骤请参阅 :doc:`/get-started/linux-macos-setup`。要在工具链中启用对 64 位 ``time_t`` 的支持，您需要在构建工具链之前从 ``crosstool-NG/samples/xtensa-esp32-elf/crosstool.config`` 文件中删除 ``--enable-newlib-long-time_t`` 选项。
+为了解决这一问题，可以使用整数部分的 MSB（惯例为位 0）来表示 1968 年到 2104 年之间的时间范围（查看 `RFC2030 <https://www.rfc-editor.org/rfc/rfc2030>` 了解更多信息），这一惯例将使得 SNTP/NTP 时间戳的生命周期延长。该惯例会在 lwIP 库的 SNTP 模块中实现，因此 ESP-IDF 中 SNTP 相关功能在 2104 年之前能够经受住时间的考验。
 
-如需使程序同时兼容 32 位和 64 位的 ``time_t``，可以使用以下方法：
 
-- 在 C 或 C++ 源文件中，如果 ``time_t`` 是 32 位的，编译器会预定义 ``_USE_LONG_TIME_T`` 宏，该宏定义在 ``<sys/types.h>`` 中。
-- 在 CMake 文件中，ESP-IDF 构建属性 ``TIME_T_SIZE`` 将被设置为 ``time_t`` 的大小，单位为字节。您可以调用 ``idf_build_get_property(var TIME_T_SIZE)`` 来获取该属性的值，并将其放入 CMake 变量 ``var`` 中。了解更多关于 ``idf_build_get_property`` 的信息，参见 :ref:`ESP-IDF CMake 构建系统 API <cmake_buildsystem_api>`。
+Unix 时间 2038 年溢出问题
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-注意， ``time_t`` 类型的大小也会影响其他类型的大小，例如 ``struct timeval``、 ``struct stat`` 和 ``struct utimbuf``。
+Unix 时间（类型 ``time_t``）此前为有符号的 32 位整数，因此将于 2038 年溢出（即 `Y2K38 问题 <https://zh.wikipedia.org/wiki/2038%E5%B9%B4%E9%97%AE%E9%A2%98>`_）。为了解决 Y2K38 问题，ESP-IDF 从 v5.0 版本起开始使用有符号的 64 位整数来表示 ``time_t``，从而将 ``time_t`` 溢出推迟 2920 亿年。
 
 
 API 参考