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‎2023/08/rcore_os_lab1_qemu_gdb.md

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# [rcore lab1 qemu gdb](/2023/08/rcore_os_lab1_qemu_gdb)
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yay -S riscv-gnu-toolchain-bin
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riscv64-unknown-elf-gdb: error while loading shared libraries: libpython3.8.so.1.0
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从 ubuntu20.04 拷贝 libpython3.8.so 之后
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> Fatal Python error: init_fs_encoding: failed to get the Python codec of the filesystem encoding
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Python runtime state: core initialized
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好吧还是从 https://github.com/riscv-collab/riscv-gnu-toolchain 源码安装
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结果 make linux 卡在 `git clone submodule`... 所以 rcore 官方教程推荐下载 <https://static.dev.sifive.com/dev-tools/riscv64-unknown-elf-gcc-8.3.0-2020.04.1-x86_64-linux-ubuntu14.tar.gz>
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---
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## rcore 实验一
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<http://rcore-os.cn/rCore-Tutorial-Book-v3/chapter1/4first-instruction-in-kernel2.html?highlight=strip%20all>
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先掌握下作业题和实验代码的方法论，在操作系统训练营中
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- 作业题通常是 github classroom 克隆一份代码仓库 make rustlings 解决完编译错误提交代码跑 CI 打分
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- 实验题通常是克隆一个代码仓库，例如实验一就 git checkout ch1 最后 make run
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由于 makefile 没有 `set -x` 我也不熟悉，我把 rcore 实验一的 makefile 代码整理成 shell 脚本
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```sh
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<<- EOF
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[build]
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target = "riscv64gc-unknown-none-elf"
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[target.riscv64gc-unknown-none-elf]
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rustflags = [
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"-Clink-arg=-Tsrc/linker.ld", "-Cforce-frame-pointers=yes"
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]
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EOF
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cargo clean
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cp src/linker-qemu.ld src/linker.ld
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cargo b
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# objcopy --only-section copy code/data section only?
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target=target/riscv64gc-unknown-none-elf/debug
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riscv64-unknown-elf-objcopy $target/os --strip-all -O binary $target/os.bin
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qemu-system-riscv64 -machine virt -nographic \
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-bios ../bootloader/rustsbi-qemu.bin \
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-s -S \
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-device loader,file=$target/os.bin,addr=0x80200000
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```
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`-device` 告诉 qemu 帮忙将二进制镜像加载到内存指定位置
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想着 gdb 能看点函数符号，我尝试去掉 --strip-all 结果 qemu 一运行就卡死了
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我的思考是 0x802 内存地址必须紧凑排满生成出的代码块，因此就不能 debug symbol? 这里我没想明白，linux kernel 确实也有 debug symbol 相关配置
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解答: 看本文后续 ELF section 解释以及 linker-qemu.ld 源码中都是将各个 section 位置写死装载到内存中
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## qemu gdb 初体验
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> riscv64-unknown-elf-gdb -ex 'file target/riscv64gc-unknown-none-elf/debug/os' -ex 'set arch riscv:rv64' -ex 'target remote localhost:1234'
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ubuntu 用 gdb-multiarch 亦可
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用 `i r` 命令也就是 info registers 的缩写看看寄存器的值
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`i r mstatus` 能看一些特殊寄存器
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结果全是 0 只有当前执行指令地址的 pc 寄存器有值 0x1000
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```
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(gdb) x/10x 0x1000
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0x1000: 0x00000297 0x02828613 0xf1402573 0x0202b583
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0x1010: 0x0182b283 0x00028067 0x80000000 0x00000000
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0x1020: 0x87e00000 0x00000000
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```
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用 `x /10x 0x1000` 命令看内存地址 0x1000 开始，往后看 10 个 32bit，x 表示用 16 进制显示
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由于 RustSBI 版本有所变动，所以这 10 个指令内容跟书中不一样很正常
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## vscode gdb 看不到寄存器
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毕竟内核代码是编译出来的 ELF 文件 strip 掉一堆元信息，vscode 调试窗口看不到变量值，估计 CLion 也是看不到
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```json
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{
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"name": "rcore-os",
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"type": "cppdbg",
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"request": "launch",
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"program": "${workspaceFolder}/os/target/riscv64gc-unknown-none-elf/debug/os",
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"args": [
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"-ex",
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"file target/riscv64gc-unknown-none-elf/debug/os",
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"-ex",
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"set arch riscv:rv64"
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],
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"stopAtEntry": false,
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"cwd": "${workspaceFolder}",
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"environment": [],
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"externalConsole": false,
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"MIMode": "gdb",
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"setupCommands": [
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{
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"description": "",
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"text": "-enable-pretty-printing",
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"ignoreFailures": true
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}
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],
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"miDebuggerPath": "/home/w/files/apps/riscv64_toolchain/bin/riscv64-unknown-elf-gdb",
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"miDebuggerServerAddress": "localhost:1234"
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}
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```
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## 常用工具使用方法笔记
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http://rcore-os.cn/rCore-Tutorial-Book-v3/appendix-b/index.html#
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### readelf/rust-readobj
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readelf -h os/target/riscv64gc-unknown-none-elf/debug/os
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```
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ELF Header:
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Magic: 7f 45 4c 46 02 01 01 00 00 00 00 00 00 00 00 00
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Class: ELF64
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Data: 2's complement, little endian
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Version: 1 (current)
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OS/ABI: UNIX - System V
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ABI Version: 0
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Type: EXEC (Executable file)
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Machine: RISC-V
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```
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rust-readobj require cargo-binutils and rustup llvm-tools-preview component
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rust-readobj -all os/target/riscv64gc-unknown-none-elf/debug/os | head
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```
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File: os/target/riscv64gc-unknown-none-elf/debug/os
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Format: elf64-littleriscv
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Arch: riscv64
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AddressSize: 64bit
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LoadName: <Not found>
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ElfHeader {
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Ident {
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Magic: (7F 45 4C 46)
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Class: 64-bit (0x2)
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```
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Magic 前 4 byte 是固定组合让加载器快速确定文件是不是一个 ELF
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text section 就是代码段一般在前两个位置 text section 的例子
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```
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Section {
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Index: 1
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Name: .text (1)
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Type: SHT_PROGBITS (0x1)
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Flags [ (0x6)
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SHF_ALLOC (0x2)
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SHF_EXECINSTR (0x4)
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]
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Address: 0x80200000
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Offset: 0x1000
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Size: 21684
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```
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当将程序加载到内存的时候，对于每个 program header 所指向的区域，我们需要将对应的数据从文件复制到内存中
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!> 这也是为什么 cargo b 编译出 elf 必须 strip-all 去掉所有无关 section 才能让首个地址才是代码
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由于实验一代码限定死了内存布局，只有 strip-all 才能让我们手动完成【加载】任务
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说起 ELF 文件加载想起一本必须要看的经典书《程序员的自我修养：链接、装载与库》
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### ELF 三个核心 section
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- text: 放代码和常量
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- bss: 未初始化的 static 变量
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- data: 已初始化的 static 变量
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## objdump 反汇编
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rust-objdump -all target/riscv64gc-unknown-none-elf/release/os
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可以去找下 main/_start 的汇编代码
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## objcopy
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实验一中已经用熟练了

‎2023/08/riscv_asm_swap_two_integer.md

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|x10,x11|a0,a1|function argument or return value register|
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|x12,x17|a2,a7|function argument register|
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除了 general register 还有以下几个特殊寄存器
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- pc: Program Counter, address of the current instruction being executed
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## 试试编译汇编
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我还不会写汇编，可以先写出 C 代码编译出汇编来学习下

‎2023/08/riscv_qemu_opensbi.md

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## qemu 命令解读
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以 mit-pdos/xv6-riscv 仓库的 make qemu 为例
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> qemu-system-riscv64 -machine virt -bios none -kernel kernel/kernel -m 128M -smp 3 -nographic -global virtio-mmio.force-legacy=false -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0

‎README.md

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- [文章列表 - 吴翱翔的博客](/)
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- [正在读的书](/books.md)
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- **2023-08**
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- [qemu vscode gdb](/2023/08/qemu_riscv_vscode_gdb.md)
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- [gcc/ld --as-needed](/2023/08/gcc_ld_as_needed.md)
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- [dumpbin](/2023/08/dumpbin_ldd_alternative_on_windows.md)
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- [ptr::addr_of!](/2023/08/ptr_addr_of.md)

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