Fix stdio newlib v2

[loremmoqi]

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)

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对于下面的问题添加了详细的代码注释。
当前 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

]

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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
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• 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]

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[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: 2025-10-11 14:28 CST)

• ⌛ @GorrayLi Pending Review
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• ⌛ @mysterywolf Pending Review

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1 out of 2 committers have signed the CLA.

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[BernardXiong]

AI给出的信息

你分析得完全正确：
不同版本的 newlib 对 _GLOBAL_REENT->__sdidinit 的定义不同，3.4.0 及以后部分版本（特别是 small reent）已经移除了该成员。直接访问会导致编译错误或未定义行为，因此需要根据实际 newlib 版本和编译选项做兼容。

更可靠的跨版本兼容方案

目前的写法：

#if defined(_REENT_SMALL) || !defined(__sdidinit)
// do nothing
#else
    _GLOBAL_REENT->__sdidinit = 1;
#endif

这种判断虽然可以解决部分情况，但通常 newlib 官方建议用更严谨的宏判断。实际上，newlib 从 3.4.0 开始逐步移除了 __sdidinit，而且有些定制版本可能行为不同。

推荐做法

1. 判断 NEWLIB_VERSION_NUM 是否小于 3.4.0（即 30400U），只有在旧版时才设置该字段。
2. 再加一层保护：仅当 _GLOBAL_REENT 结构体内存在 __sdidinit 成员时才访问，防止自定义 newlib 版本导致的潜在问题。

可选：用结构体成员检测宏（如 offsetof 或手动宏定义）进一步防护。

代码实现与注释（英文）

#include <stdio.h>
#include <reent.h>
#include <fcntl.h>
#include <rtthread.h>

/**
 * Initialize the standard IO streams for RT-Thread when using Newlib.
 * This function sets up the global reentrancy structure's standard streams,
 * and configures legacy fields for compatibility with different Newlib versions.
 *
 * Compatibility notes:
 * - In Newlib versions prior to 3.4.0, the __sdidinit field exists and needs to be set.
 * - In Newlib 3.4.0 and later, or when using the "small reent" configuration, __sdidinit is removed.
 * - Accessing __sdidinit when it does not exist causes build errors.
 * - This code uses version checks and macro guards to ensure safe access.
 */
void rt_posix_stdio_init(void)
{
    FILE *std_console = NULL;
    int std_fd = -1;

    /* (Other initialization code omitted for brevity) */

    _GLOBAL_REENT->_stdin = std_console;
    _GLOBAL_REENT->_stdout = std_console;
    _GLOBAL_REENT->_stderr = std_console;

    /*
     * For Newlib versions < 3.4.0, set the legacy __sdidinit field.
     * This field is obsolete and removed in newer versions or in small reent mode.
     * The macro NEWLIB_VERSION_NUM is provided by Newlib headers.
     */
#if defined(NEWLIB_VERSION_NUM) && (NEWLIB_VERSION_NUM < 30400U)
    /* __sdidinit is present, set to 1 to indicate stdio streams are initialized */
    _GLOBAL_REENT->__sdidinit = 1;
#endif
    /*
     * For custom or unknown Newlib versions, if __sdidinit is defined in _reent,
     * you may add extra macro checks here for higher safety.
     */
}

补充说明

• 若你的 toolchain 没有定义 NEWLIB_VERSION_NUM，可通过 CMake 或 makefile 手动传递宏定义，或者用 #ifdef 保护。
• 如果担心极端情况下 NEWLIB_VERSION_NUM 也没有、但 __sdidinit 还在，可以用如下宏补充：

#if (!defined(NEWLIB_VERSION_NUM) && defined(__sdidinit)) || \
     (defined(NEWLIB_VERSION_NUM) && (NEWLIB_VERSION_NUM < 30400U))
    _GLOBAL_REENT->__sdidinit = 1;
#endif

英文注释重点

• Clearly state which Newlib versions require setting __sdidinit.
• Explain why the check is necessary (struct member may not exist).
• Mention that directly accessing __sdidinit in newer Newlib versions will cause build errors.
• Note that the macro NEWLIB_VERSION_NUM is key for version detection.

---

Summary:
Use version macros to guard the access of _GLOBAL_REENT->__sdidinit, and clearly annotate the reason for compatibility. This ensures smooth compilation and execution regardless of Newlib version in RT-Thread’s POSIX layer.