如何在 32 位时间库中使用 mktime64()、time64() 和 localtime64() 函数? [英] How to use mktime64(), time64() and localtime64() function with 32-bit time library?

问题描述

如何在带有 32 位时间库的 Linux 中使用 mktime64() 避免 2038 年问题?

我们尝试使用宏 _Time64 但失败了，因为编译器仍然抛出 undefined mktime64() 错误:

typedef long long _Time64_t;_Time64_t _Time64(_Time64_t *pt);struct tm *_Localtime64(_Time64_t *pt);_Time64_t _mktime64(_Time64_t pt);

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main.c:(.text+0x68): 对 `_mktime64' 的未定义引用

你能帮我如何使用 32 位库的 mktime64、time64 和 localtime64 函数吗?

解决方案

C 标准库 (CRT) 仅适用于 Linux有一个 time_t 类型，所以 没有 _mktime64 适合你

在 32 位 Windows 上有 2 种不同的 time_t 类型(__time32_t 和 __time64_t) 和 2每个时间函数的版本(如 _mktime32 和 _mktime64) 只是因为微软逐渐在他们的 CRT 中添加了 64 位时间支持而没有破旧代码.time_t 或 mktime 等标准标识符实际上是宏，将定义为所需的 32 位或 64 位版本.time_t 在 VS2015 中默认更改为 64 位，因此从那时起编译的所有应用程序都不会遇到 2038 年的问题.欲了解更多信息，请阅读 另看2038年的问题

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Linux CRT 通过立即将 time_t 更改为 64 位类型来解决 2038 年问题，无需任何渐进的中间步骤.这发生在运行在 Linux 内核 5.6 或更高版本上的 32 位 glibc 2.32+ 和 musl 1.2+ 中.所以要避免 32 位 Linux 上的 2038 年问题，您必须使用足够新的内核和 CRT

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• 所有用户空间都必须使用 64 位 time_t 编译，即将发布的 musl-1.2 和 glibc-2.32 版本以及来自 linux-5.6 或更高版本的已安装内核头文件将支持该代码.
• 直接使用系统调用接口的应用程序需要移植以使用linux-5.1中添加的time64系统调用来代替现有的系统调用.这会影响 futex() 和 seccomp() 的大多数用户以及拥有自己的不基于 libc 的运行时环境的编程语言.

https://lkml.org/lkml/2020/1/29/355?anz=web

如果您无法升级 CRT 和内核版本，那么您需要使用 3^rd 方库，例如 evalEmpire/y2038

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这是 POSIX time.h 的实现，它解决了 time_t 只有 32 位的系统上的 2038 年错误.它是在沼泽标准 ANSI C 中实现的.

如果您的内核版本在 5.1 和 5.6 之间，那么您也可以编写自己的包装函数，因为 32 位平台上的 64 位时间支持是 引入到 Linux 5.1 内核，添加了新的 *time64 系统调用

欲了解更多信息，请阅读

• 接近内核 2038 年终局
• 64 位时间符号处理GNU C 库
• glibc Y2038 证明设计
• 将 time_t 和 clock_t 更改为 64 位
• 看看各种系统中的 2036/2038 年问题和时间证明

How to use the mktime64() in Linux with 32-bit time library to avoid the year 2038 issue?

We have tried using the macro _Time64 but failed as compiler still throws undefined mktime64() error:

typedef long long _Time64_t;

_Time64_t _Time64(_Time64_t *pt);

struct tm *_Localtime64(_Time64_t *pt);

_Time64_t _mktime64(_Time64_t pt);

main.c:(.text+0x68): undefined reference to `_mktime64'

Could you please help me how to use the mktime64, time64 and localtime64 function using 32-bit library?

解决方案

C standard libraries (CRT) on Linux only has one time_t type so there's no _mktime64 for you

On 32-bit Windows there are 2 different time_t types (__time32_t and __time64_t) and 2 versions of each time functions (like _mktime32 and _mktime64) just because Microsoft gradually added 64-bit time support to their CRT without breaking old code. Standard identifiers like time_t or mktime are actually macros that will be defined as the desired 32 or 64-bit version. time_t was changed to 64-bit by default in VS2015 so all apps compiled since then will not suffer from year 2038 problem. For more information read Another look at the year 2038 problem

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Linux CRTs address the year 2038 issue by changing time_t to a 64-bit type immediately without any gradual intermediate steps. That happened in 32-bit glibc 2.32+ and musl 1.2+ running on Linux kernel 5.6 or later. So to avoid the year 2038 issue on 32-bit Linux you must be on a new enough kernel and CRT

• All user space must be compiled with a 64-bit time_t, which will be supported in the coming musl-1.2 and glibc-2.32 releases, along with installed kernel headers from linux-5.6 or higher.
• Applications that use the system call interfaces directly need to be ported to use the time64 syscalls added in linux-5.1 in place of the existing system calls. This impacts most users of futex() and seccomp() as well as programming languages that have their own runtime environment not based on libc.

https://lkml.org/lkml/2020/1/29/355?anz=web

If you can't upgrade the CRT and kernel version then you need to use a 3^rd party library like evalEmpire/y2038

This is an implementation of POSIX time.h which solves the year 2038 bug on systems where time_t is only 32 bits. It is implemented in bog-standard ANSI C.

If your kernel version is between 5.1 and 5.6 then you can also write your own wrapper functions because 64-bit time support on 32-bit platforms was introduced to the Linux 5.1 kernel with the addition of the new *time64 syscalls

For more information read

• Approaching the kernel year-2038 end game
• 64-bit time symbol handling in the GNU C Library
• glibc Y2038 Proofness Design
• Change time_t and clock_t to 64 bit
• A look at the Year 2036/2038 problems and time proofness in various systems

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