Merge pull request #4 from Richard-Qin-001/dev/shell

Rebuilt the system's underlying structure; it is now stable enough to merge. 

The system now supports a read-only file system and has a simple shell implemented.

4 files changed, 154 insertions, 0 deletions

diff --git a/docs/debug/debug_slab.md b/docs/debug/debug_slab.md
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+++ b/docs/debug/debug_slab.md
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+# Debug
+
+发现user_init加载之后无法正常跳转到shell
+
+检查fork
+
+添加调试信息
+```cxx
+printf("fork start\n");
+int pid = fork();
+printf("fork suceess, pid=%i\n", pid);
+```
+正常打印，fork()没有问题
+
+尝试在 'exec(sh_path, argv);' 前后添加调试信息
+
+该代码之前有输出，之后无输出
+
+尝试解决exec.cc的问题
+
+在exec()函数开头处添加调试信息
+
+```CXX
+        Drivers::uart_puts("Enter Exec\n");
+        // Get Inode
+        Inode *raw_ip = VFS::namei(path);
+        if (!raw_ip)
+            return -1;
+        InodeGuard iguard(raw_ip);
+```
+
+没有输出
+
+怀疑是系统注册的问题，但不可能，因为在实现shell之前的简易测试程序证明系统调用没有问题
+
+尝试 GDB 调试
+
+![alt text](debug_slab_1.png)
+
+发现卡在 sret 返回的部分，跳转的地址没有问题，但是卡死，说明CPU没有跑飞，可能遇到了死循环
+
+检查sys_exec()
+
+通过在每行代码前后添加打印调试信息，发现问题出在这行代码：
+```cxx
+        kargv.args[i] = (char *)Slab::kmalloc(KernelArgv::MAX_ARG_LEN);
+```
+这行代码之后的打印信息没有输出，说明这里一直在执行！
+
+检查Slab
+
+像之前一样通过在每行代码前后添加打印调试信息，发现问题出在这里：
+```cxx
+for (uint i = 0; i < c->obj_count_per_slab - 1; i++)
+        {
+            // The content of the i-th object is i+1
+            uint16 *ptr = (uint16 *)(base + i * c->obj_size);
+            *ptr = i + 1;
+        }
+```
+这段代码之前的信息可以输出，之后的不能输出，说明这里出问题了
+
+在循环内部打印信息，发现调试信息刷屏
+
+证明了在GDB里面看到的消息，并不是CPU跑到了某些神秘地址，而是一直卡在这个死循环！
+
+这里出现了死循环，说明这里循环终止条件出了问题，根本原因需要排查
+
+可能是错误的计算，导致这里成了ull的最大值，即使在 3 GHz CPU 上跑空循环，跑满 unsigned long long 最大值次数也需要 近千年。
+
+怀疑之前这个值是0
+
+添加代码：
+```cxx
+    if (c->obj_count_per_slab == 0)
+        Drivers::uart_puts("it is 0");
+```
+证明猜测正确
+
+这里检查发现这个值确实是0，但它为什么能是0呢？
+
+可能是初始化的问题？？？？
+
+检查系统初始化main.cc
+
+发现Slab确实没有初始化，导致c->obj_count_per_slab这个值一直是0！
+
+初始化！
+
+正常加载shell
+
+说明 ELF 加载，只读 FAT32 文件系统 正常实现
+
+该bug解决
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diff --git a/docs/debug/debug_slab_1.png b/docs/debug/debug_slab_1.png
new file mode 100644
index 0000000..5cb9e66
--- /dev/null
+++ b/docs/debug/debug_slab_1.png
diff --git a/docs/dev/dev_device.md b/docs/dev/dev_device.md
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+++ b/docs/dev/dev_device.md
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+# Dev log
+## **3.Device Model & HAL:**
+* Interrupt Controller: PLIC:
+
+    * Implement the PLIC (Platform-Level Interrupt Controller) driver.
+
+    * Set the PLIC priority threshold and enable bits during the start() phase.
+
+    * Dispatch Cause 9 (External Interrupt) in kerneltrap/usertrap.
+
+* Character Device: Interrupt-Driven Console:
+
+    * Implement a Ring Buffer. uart_putc returns immediately after writing to the buffer.
+
+    * UART transmit interrupt: triggers when the serial port is idle, the ISR takes data from the Ring Buffer and writes it to the register.
+
+    * UART receive interrupt: triggers when a key is pressed, the ISR reads the character and wakes up the process waiting to read.
+
+* Block Device: VirtIO-Blk:
+
+    * Implement a block device driver for the PCI or MMIO transport layer according to the VirtIO 2.0 standard.
+
+    * DMA: Use the Buddy System to allocate contiguous memory as the descriptor table for the Virtqueue.
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diff --git a/docs/dev/dev_memory.md b/docs/dev/dev_memory.md
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index 0000000..f05e336
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+++ b/docs/dev/dev_memory.md
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+# Dev log 
+## **1. Process Management:** 
+The core architecture has been upgraded from a simple single queue to a Per-CPU scheduler, supporting multi-core concurrency. 
+
+* Process lifecycle: A complete process state machine has been implemented, including UNUSED, RUNNABLE, RUNNING, SLEEPING, and ZOMBIE states. 
+
+* Core operations: 
+    * fork(): process cloning, supporting COW (copy-on-write) isolation of memory space between parent and child processes. 
+    * exit(): process termination and resource cleanup. 
+    * wait(): parent process waits for child process to exit. 
+    * sleep()/wakeup(): channel-based sleep and wakeup mechanism. 
+
+* Scheduling algorithm: 
+    * O(1) priority scheduling has been implemented (supporting 4 priority queues). 
+
+    * Per-CPU RunQueue: each CPU has its own independent run queue. 
+
+    * Supports Work Stealing: idle CPUs can fetch tasks from other CPUs’ queues. 
+
+## **2. Memory Management:** 
+A complete virtual and physical memory management system has been implemented. 
+
+* Physical Memory (PMM): Implements the Buddy System, supporting memory allocation and deallocation in $2^n$ pages. 
+
+* Virtual Memory (VM): Based on RISC-V Sv39 paging mode. Provides secure data copying from user space to kernel space (copyin). 
+
+* COW (Copy-On-Write): During fork, only page table entries are copied and pages are set to read-only; writes trigger page faults for physical copy, greatly improving process creation efficiency. 
+
+* Kernel heap: Implements a Slab Allocator, providing efficient allocation of small objects (such as struct Proc). 
+
+## **3. Synchronization:**
+
+* Spinlock: Used to protect very short critical sections (e.g., scheduler lock, PMM lock), supports disabling interrupts to prevent deadlocks. 
+
+* Mutex (sleeping lock): Used for long critical sections (e.g., file I/O), allowing sleep while holding the lock. 
+
+* Lock Handoff: Implements a complex lock handoff mechanism in the scheduler to ensure atomicity of context switches. 
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