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<ol class="chapter"><li class="chapter-item expanded affix "><a href="index.html">简明 zCore 教程</a></li><li class="chapter-item expanded affix "><a href="zcore-intro.html">🚧 zCore 整体结构和设计模式</a></li><li class="chapter-item expanded affix "><a href="fuchsia.html">🚧 Fuchsia OS 和 Zircon 微内核</a></li><li class="chapter-item expanded "><a href="ch01-00-object.html"><strong aria-hidden="true">1.</strong> 内核对象</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch01-01-kernel-object.html"><strong aria-hidden="true">1.1.</strong> ✅ 初识内核对象</a></li><li class="chapter-item expanded "><a href="ch01-02-process-object.html"><strong aria-hidden="true">1.2.</strong> 🚧 对象管理器：Process 对象</a></li><li class="chapter-item expanded "><a href="ch01-03-channel-object.html"><strong aria-hidden="true">1.3.</strong> 🚧 对象传送器：Channel 对象</a></li></ol></li><li class="chapter-item expanded "><a href="ch02-00-task.html"><strong aria-hidden="true">2.</strong> 任务管理</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch02-01-zircon-task.html"><strong aria-hidden="true">2.1.</strong> 🚧 Zircon 任务管理体系</a></li><li class="chapter-item expanded "><a href="ch02-02-process-job-object.html"><strong aria-hidden="true">2.2.</strong> 🚧 进程管理：Process 与 Job 对象</a></li><li class="chapter-item expanded "><a href="ch02-03-thread-object.html"><strong aria-hidden="true">2.3.</strong> 🚧 线程管理：Thread 对象</a></li></ol></li><li class="chapter-item expanded "><a href="ch03-00-memory.html"><strong aria-hidden="true">3.</strong> 内存管理</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch03-01-zircon-memory.html"><strong aria-hidden="true">3.1.</strong> 🚧 Zircon 内存管理模型</a></li><li class="chapter-item expanded "><a href="ch03-02-vmo.html"><strong aria-hidden="true">3.2.</strong> 🚧 物理内存：VMO 对象</a></li><li class="chapter-item expanded "><a href="ch03-03-vmo-paged.html"><strong aria-hidden="true">3.3.</strong> 🚧 物理内存：按页分配的 VMO</a></li><li class="chapter-item expanded "><a href="ch03-04-vmar.html"><strong aria-hidden="true">3.4.</strong> 🚧 虚拟内存：VMAR 对象</a></li></ol></li><li class="chapter-item expanded "><a href="ch04-00-userspace.html"><strong aria-hidden="true">4.</strong> 用户程序</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch04-01-user-program.html"><strong aria-hidden="true">4.1.</strong> 🚧 Zircon 用户程序</a></li><li class="chapter-item expanded "><a href="ch04-02-context-switch.html" class="active"><strong aria-hidden="true">4.2.</strong> 🚧 上下文切换</a></li><li class="chapter-item expanded "><a href="ch04-03-syscall.html"><strong aria-hidden="true">4.3.</strong> 🚧 系统调用</a></li></ol></li><li class="chapter-item expanded "><a href="ch05-00-signal-and-waiting.html"><strong aria-hidden="true">5.</strong> 信号和等待</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch05-01-wait-signal.html"><strong aria-hidden="true">5.1.</strong> 🚧 等待内核对象的信号</a></li><li class="chapter-item expanded "><a href="ch05-02-port-object.html"><strong aria-hidden="true">5.2.</strong> 🚧 同时等待多个信号：Port 对象</a></li><li class="chapter-item expanded "><a href="ch05-03-more-signal-objects.html"><strong aria-hidden="true">5.3.</strong> 🚧 实现更多：EventPair, Timer 对象</a></li><li class="chapter-item expanded "><a href="ch05-04-futex-object.html"><strong aria-hidden="true">5.4.</strong> 🚧 用户态同步互斥：Futex 对象</a></li></ol></li><li class="chapter-item expanded "><a href="ch06-00-hal.html"><strong aria-hidden="true">6.</strong> 硬件抽象层</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="ch06-01-zcore-hal-unix.html"><strong aria-hidden="true">6.1.</strong> ✅ UNIX硬件抽象层</a></li></ol></li></ol> </div>
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<h1 id="上下文切换"><a class="header" href="#上下文切换">上下文切换</a></h1>
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<blockquote>
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<p>本节介绍 trapframe-rs 中 <a href="https://github.com/rcore-os/trapframe-rs/blob/master/src/arch/x86_64/fncall.rs">fncall.rs</a> 的魔法实现</p>
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<h2 id="保存和恢复通用寄存器"><a class="header" href="#保存和恢复通用寄存器">保存和恢复通用寄存器</a></h2>
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<blockquote>
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<p>定义 UserContext 结构体</p>
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<p>保存 callee-saved 寄存器到栈上，恢复 UserContext 寄存器，进入用户态，反之亦然</p>
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</blockquote>
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<h2 id="找回内核上下文线程局部存储-与-fs-寄存器"><a class="header" href="#找回内核上下文线程局部存储-与-fs-寄存器">找回内核上下文：线程局部存储 与 FS 寄存器</a></h2>
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<blockquote>
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<p>在用户程序跳转回内核代码的那一刻，如何在不破坏用户寄存器的情况下切换回内核栈？</p>
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<p>进入用户态前，将内核栈指针保存在内核 glibc 的 TLS 区域中。为此我们需要查看 glibc 源码，找到一个空闲位置。</p>
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<p>Linux 和 macOS 下如何分别通过系统调用设置 fsbase / gsbase</p>
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<h2 id="测试"><a class="header" href="#测试">测试</a></h2>
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<p>编写单元测试验证上述过程</p>
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</blockquote>
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<h2 id="macos-的麻烦动态二进制修改"><a class="header" href="#macos-的麻烦动态二进制修改">macOS 的麻烦：动态二进制修改</a></h2>
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<blockquote>
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<p>由于 macOS 用户程序无法修改 fs 寄存器，当运行相关指令时会访问非法内存地址触发段错误。</p>
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<p>我们需要实现段错误信号处理函数，并在其中动态修改用户程序指令，将 fs 改为 gs。</p>
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