fix(stdio): ensure compatibility with newlib <3.4.0 by handling removed __sdidinit

[loremmoqi]

拉取/合并请求描述：(PR description)

[

为什么提交这份PR (why to submit this PR)

前 RT-Thread 在使用 newlib 的部分版本时，会出现以下问题：
在 _GLOBAL_REENT 结构中，旧版本使用的 __sdidinit 字段已被移除；

• 代码中仍然直接访问 _GLOBAL_REENT->__sdidinit，导致在编译 newlib 时出错；
• 不同版本的 newlib（如 3.3.x / 3.4.x / 4.0.0 / 4.3.0 / 12.x）在 reent 结构中存在兼容性差异。

你的解决方案是什么 (what is your solution)

在 components/libc/posix/io/stdio.c/stdio.c 中增加更合理的版本判断宏：
#if defined(_REENT_SMALL) || !defined(__sdidinit)
// Newlib >= 3.4.0 or small reent version: no __sdidinit field
// Do nothing
#else
// Older newlib versions (typically < 3.4.0) still define __sdidinit
_GLOBAL_REENT->__sdidinit = 1;
#endif

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

• BSP:bsp/qemu-vexpress-a9

• .config:无需修改 .config 文件，仅涉及代码逻辑的条件编译适配

• action:https://github.com/loremmoqi/rt-thread/blob/master/.github/workflows/manual_dist.yml

]

当前拉取/合并请求的状态 Intent for your PR

必须选择一项 Choose one (Mandatory):

• 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formatting 等源码格式化工具确保格式符合RT-Thread代码规范 This PR 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

[github-actions]

📌 Code Review Assignment

🏷️ Tag: components

Reviewers: Maihuanyi

Changed Files (Click to expand)

• components/libc/posix/io/stdio/stdio.c

🏷️ Tag: components_libc

Reviewers: GorrayLi mysterywolf

Changed Files (Click to expand)

• components/libc/posix/io/stdio/stdio.c

---

📊 Current Review Status (Last Updated: 2025-10-13 10:52 CST)

• ⌛ GorrayLi Pending Review
• ⌛ Maihuanyi Pending Review
• ⌛ mysterywolf Pending Review

---

📝 Review Instructions

1. 维护者可以通过单击此处来刷新审查状态: 🔄 刷新状态
   Maintainers can refresh the review status by clicking here: 🔄 Refresh Status

2. 确认审核通过后评论 LGTM/lgtm
   Comment LGTM/lgtm after confirming approval

3. PR合并前需至少一位维护者确认
   PR must be confirmed by at least one maintainer before merging

ℹ️ 刷新CI状态操作需要具备仓库写入权限。
ℹ️ Refresh CI status operation requires repository Write permission.

[github-actions]

👋 感谢您对 RT-Thread 的贡献！Thank you for your contribution to RT-Thread!

为确保代码符合 RT-Thread 的编码规范，请在你的仓库中执行以下步骤运行代码格式化工作流（如果格式化CI运行失败）。
To ensure your code complies with RT-Thread's coding style, please run the code formatting workflow by following the steps below (If the formatting of CI fails to run).

---

🛠 操作步骤 | Steps

1. 前往 Actions 页面 | Go to the Actions page
   点击进入工作流 → | Click to open workflow →

2. 点击 Run workflow | Click Run workflow

• 设置需排除的文件/目录（目录请以"/"结尾）
  Set files/directories to exclude (directories should end with "/")
• 将目标分支设置为 \ Set the target branch to：fix-stdio-newlib
• 设置PR number为 \ Set the PR number to：10791

3. 等待工作流完成 | Wait for the workflow to complete
   格式化后的代码将自动推送至你的分支。
   The formatted code will be automatically pushed to your branch.

完成后，提交将自动更新至 fix-stdio-newlib 分支，关联的 Pull Request 也会同步更新。
Once completed, commits will be pushed to the fix-stdio-newlib branch automatically, and the related Pull Request will be updated.

如有问题欢迎联系我们，再次感谢您的贡献！💐
If you have any questions, feel free to reach out. Thanks again for your contribution!

[loremmoqi]

This PR is ready for review. All automated checks have passed, but merging is blocked because:

✅ At least 1 approving review is required
✅ 5 workflows are awaiting manual approval (due to pull_request_target)

Could you please:

1. Review and approve this PR if it looks good?
2. Click “Approve and run” on the pending workflows?

Thanks for your time! 🙏

[Copilot]

Pull Request Overview

This PR fixes compatibility issues with newer versions of Newlib (>= 3.4.0) by updating the stdio initialization code. The __sdidinit field was removed from the _GLOBAL_REENT structure in newer Newlib versions, causing compilation errors when accessing this field directly.

Key changes:

• Replaces version-specific macro checks with feature detection
• Uses _REENT_SMALL and __sdidinit definitions to determine compatibility
• Maintains backward compatibility with older Newlib versions

[Copilot]

English: The comment style should follow RT-Thread coding standards using C-style comments (/* */) instead of C++-style comments (//) for consistency with the existing codebase.\n\n中文: 注释风格应遵循 RT-Thread 编码标准，使用 C 风格注释（/* */）而不是 C++ 风格注释（//），以与现有代码库保持一致。

Suggested change

	// Newlib >= 3.4.0 or small reent version: no __sdidinit field
	// Do nothing
	#else
	// Older newlib versions (typically < 3.4.0) still define __sdidinit
	/* Newlib >= 3.4.0 or small reent version: no __sdidinit field */
	/* Do nothing */
	#else
	/* Older newlib versions (typically < 3.4.0) still define __sdidinit */

[Rbb666]

这个麻烦作者修改下

[loremmoqi]

好的

[loremmoqi]

已修改

[loremmoqi]

@Rbb666 @supperthomas
已根据上次 review 的意见修改并重新发起了 review 请求，请帮忙再看一下，谢谢！

[supperthomas]

这边看到代码，没有修改，再check一下。

[supperthomas]

[supperthomas]

再检查下代码，目前没有修改

[loremmoqi]

这个是因为多加了一个空格，所以审核没通过，所以我把空格去掉了。

[loremmoqi]

@Rbb666 @supperthomas
我最后一次commit的是“delete extra space at the end of this line 109”，也就是去除了一个space，没有大的代码修改，请帮忙再看一下，谢谢！

[loremmoqi]

@Rbb666 @supperthomas
我重新提交了commit，没有代码修改，请帮忙再看一下，谢谢！

[supperthomas]

pull request 标题修改一下，添加前缀，参考其他PR

[loremmoqi]

收到

[loremmoqi]

已修改完成，谢谢您提意见。

[supperthomas]

感谢贡献

[loremmoqi]

谢谢各位给予修改意见让我完成本次合并。谢谢！