[libc] fix: gmtime_r mishandles timestamps before the epoch by Yunlk · Pull Request #11929 · RT-Thread/rt-thread

Yunlk · 2026-10-24T17:23:38Z

拉取/合并请求描述：(PR description)

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为什么提交这份PR (why to submit this PR)

修复 #11923。

gmtime_r() 用 C 的除法拆时间戳，而 C 的除法向零截断：

work = *timep % (24*60*60);          /* *timep < 0 时余数为负 */
work = (int)(*timep / (24*60*60));   /* 天数也是负的 */
for (i = 1970;; ++i) { ... }         /* 只能向未来遍历 */

于是负时间戳会返回一个非 NULL、但字段非法的结构体：

t	master 实际	期望
-1	`1970-01-01 00:00:-1`（wday=4 yday=0）	`1969-12-31 23:59:59`
-86400	`1970-01-00 00:00:00`（yday=-1）	`1969-12-31 00:00:00`
-31536000	`1970-01--364 00:00:00`（wday=-4 yday=-365）	`1969-01-01 00:00:00`
-2208988800	`1970-01--25566 00:00:00`（wday=-6 yday=-25567）	`1900-01-01 00:00:00`

不只是秒为负，tm_mday 和 tm_wday 也会变成明显的非法值。

你的解决方案是什么 (what is your solution)

只改 gmtime_r() 一个函数，三步：

改 floor 除法：余数为负时借一天，保证 tm_sec/tm_min/tm_hour 非负
tm_wday 用规范化后的天数计算，并保证结果落在 0~6（原来 (4 + work) % 7 在天数为负时返回负值）
年份遍历支持后退：while (work < 0) { --i; work += 闰年?366:365; }，让早于 1970 的时间戳也能定位到正确年份

__isleap() 对 1970 之前的年份本身就有效，直接复用。

请提供验证的bsp和config (provide the config and bsp)

BSP: bsp/qemu-vexpress-a9（sizeof(time_t)=8）
.config: BSP 默认配置，未改动
action: 未使用 GitHub Actions；本地 QEMU 11.0.0 + arm-none-eabi-gcc 15.2.1，master 1c801efa

同一份固件、同一个探针，改前/改后各跑一次：

t	master	本 PR
0	1970-01-01 00:00:00 wday=4	1970-01-01 00:00:00 wday=4
86399	1970-01-01 23:59:59 wday=4	1970-01-01 23:59:59 wday=4
86400	1970-01-02 00:00:00 wday=5	1970-01-02 00:00:00 wday=5
-1	1970-01-01 00:00:-1 wday=4	1969-12-31 23:59:59 wday=3
-86400	1970-01-00 00:00:00 wday=3	1969-12-31 00:00:00 wday=3
-31536000	1970-01--364 wday=-4	1969-01-01 00:00:00 wday=3
-2208988800	1970-01--25566 wday=-6	1900-01-01 00:00:00 wday=1（周一）

非负时间戳行为完全未变；1900-01-01 的 wday=1（周一）也对。

两点未包含的内容

int work 的类型没改。天数在进入年份循环时仍转 int，对 64 位 time_t 的极端值（超过约 ±580 万年）依然会截断。glibc 在那种情况下返回 EOVERFLOW，但这与 [Bug] [libc] gmtime_r 对负时间戳返回非法日历字段 #11923 是两件事，没有混进本次改动。
utest 暂未加入。可以在 components/libc/compilers/common/utest/time_tc.c 里挂 -1 与 -86400 两个用例，但需要先确认它归属哪个 Kconfig、以及哪些跑 utest 的 BSP 会执行到。若维护者认可当前改法，我可以补上用例后更新本 PR。

]

当前拉取/合并请求的状态 Intent for your PR

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本拉取/合并请求是一个草稿版本 This PR is for a code-review and is intended to get feedback
本拉取/合并请求是一个成熟版本 This PR is mature, and ready to be integrated into the repo

代码质量 Code Quality：

我在这个拉取/合并请求中已经考虑了 As part of this pull request, I've considered the following:

已经仔细查看过代码改动的对比 Already check the difference between PR and old code
代码风格正确，包括缩进空格，命名及其他风格 Style guide is adhered to, including spacing, naming and other styles
没有垃圾代码，代码尽量精简，不包含#if 0代码，不包含已经被注释了的代码 All redundant code is removed and cleaned up
所有变更均有原因及合理的，并且不会影响到其他软件组件代码或BSP All modifications are justified and not affect other components or BSP
对难懂代码均提供对应的注释 I've commented appropriately where code is tricky
代码是高质量的 Code in this PR is of high quality
已经使用clang-format 源码格式化工具确保格式符合RT-Thread代码规范 This PR has been formatted with clang-format and complies with RT-Thread code specification
如果是新增bsp, 已经添加ci检查到.github/ALL_BSP_COMPILE.json 详细请参考链接BSP自查

gmtime_r() split the timestamp with C division, which truncates toward zero: work = *timep % (24*60*60); /* negative remainder for *timep < 0 */ work = (int)(*timep / (24*60*60)); For a negative timestamp both the day count and the remainder come out negative, and the year loop below could only walk forward from 1970, so the result was returned as a valid struct tm holding impossible fields: -1 -> 1970-01-01 00:00:-1 (want 1969-12-31 23:59:59) -86400 -> 1970-01-00 00:00:00 (want 1969-12-31 00:00:00) -31536000 -> 1970-01--364 00:00:00 (want 1969-01-01 00:00:00) -2208988800 -> 1970-01--25566 00:00:00 (want 1900-01-01 00:00:00) Normalise to floor division first (borrow one day when the remainder is negative), compute tm_wday from the normalised day count while keeping the modulo result non-negative, and let the year walk run backwards for negative day counts. Verified on bsp/qemu-vexpress-a9 (QEMU 11.0.0, arm-none-eabi-gcc 15.2.1, sizeof(time_t) = 8), same probe run against master and against this patch: t master patched 0 1970-01-01 00:00:00 wday=4 1970-01-01 00:00:00 wday=4 86399 1970-01-01 23:59:59 wday=4 1970-01-01 23:59:59 wday=4 86400 1970-01-02 00:00:00 wday=5 1970-01-02 00:00:00 wday=5 -1 1970-01-01 00:00:-1 wday=4 1969-12-31 23:59:59 wday=3 -86400 1970-01-00 00:00:00 wday=3 1969-12-31 00:00:00 wday=3 -31536000 1970-01--364 wday=-4 1969-01-01 00:00:00 wday=3 -2208988800 1970-01--25566 wday=-6 1900-01-01 00:00:00 wday=1 Non-negative timestamps are unchanged; 1900-01-01 correctly reports Monday. Refs RT-Thread#11923

github-actions · 2026-10-24T17:25:04Z

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github-actions · 2026-10-24T17:27:23Z

📌 Code Review Assignment

🏷️ Tag: components

Reviewers: @Maihuanyi

Changed Files (Click to expand)

components/libc/compilers/common/ctime.c

🏷️ Tag: components_libc

Reviewers: @GorrayLi @mysterywolf

Changed Files (Click to expand)

components/libc/compilers/common/ctime.c

📊 Current Review Status (Last Updated: 2026-10-25 01:27 CST)

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维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
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github-actions · 2026-10-24T19:55:18Z

MemBrowse Memory Report · Explore what changed →

k230

SRAM: .eh_frame +8 B (+0.0%, 1,128,547 B / 268,300,288 B, total: 0% used)

loongson-ls1cdev

Code: .text +264 B (+0.1%, 363,624 B)

nuvoton-m487

CODE: .text +112 B (+0.0%, 356,288 B / 524,288 B, total: 68% used)

simulator

Code: .rela.dyn +600 B, .rodata +96 B, .text +552 B (+0.0%, 2,674,268 B)
Data: .data +640 B (+0.0%, 1,609,924 B)

wch-ch32v208w-r0

FLASH: .text +280 B (+0.2%, 159,880 B / 491,520 B, total: 33% used)

x86

Code: .text +128 B (+0.1%, 199,053 B)

No memory changes detected for:

_{Catch memory regressions in CI with MemBrowse. Free for open source.}

Yunlk requested a review from mysterywolf as a code owner October 24, 2026 17:23

github-actions Bot added the Component label Oct 24, 2026

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[libc] fix: gmtime_r mishandles timestamps before the epoch - #11929

[libc] fix: gmtime_r mishandles timestamps before the epoch#11929
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Yunlk commented Oct 24, 2026

拉取/合并请求描述：(PR description)

为什么提交这份PR (why to submit this PR)

你的解决方案是什么 (what is your solution)

请提供验证的bsp和config (provide the config and bsp)

两点未包含的内容

当前拉取/合并请求的状态 Intent for your PR

代码质量 Code Quality：

Uh oh!

github-actions Bot commented Oct 24, 2026

🛠 操作步骤 | Steps

Uh oh!

github-actions Bot commented Oct 24, 2026

📌 Code Review Assignment

🏷️ Tag: components

🏷️ Tag: components_libc

📊 Current Review Status (Last Updated: 2026-10-25 01:27 CST)

📝 Review Instructions

Uh oh!

github-actions Bot commented Oct 24, 2026

MemBrowse Memory Report · Explore what changed →

k230

loongson-ls1cdev

nuvoton-m487

simulator

wch-ch32v208w-r0

x86

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This branch has not been deployed

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