更好的阅读体验

官方文档：pdos.csail.mit.edu/6.828/2020/…
官方指导：pdos.csail.mit.edu/6.S081/2021…

安装XV6

apt-get update
sudo apt-get install git build-essential gdb-multiarch qemu-system-misc gcc-riscv64-linux-gnu binutils-riscv64-linux-gnu

The latest xv6 source and text are available via

git clone git://github.com/mit-pdos/xv6-riscv.git

and

git clone git://github.com/mit-pdos/xv6-riscv-book.git

cd xv6-riscv
make qemu

在这里插入图片描述

安装成功

指针预备知识

#include <stdio.h>
#include <stdlib.h>

void f(void) {
    int a[4];
    int *b = malloc(16);
    int *c;
    int i;

    printf("1: a = %p, b = %p, c = %p\n", a, b, c);

    c = a;
    for (i = 0; i < 4; i++)
	a[i] = 100 + i;
    c[0] = 200;
    printf("2: a[0] = %d, a[1] = %d, a[2] = %d, a[3] = %d\n",
	   a[0], a[1], a[2], a[3]);

    c[1] = 300;
    *(c + 2) = 301;
    3[c] = 302;
    printf("3: a[0] = %d, a[1] = %d, a[2] = %d, a[3] = %d\n",
	   a[0], a[1], a[2], a[3]);

    c = c + 1;
    *c = 400;
    printf("4: a[0] = %d, a[1] = %d, a[2] = %d, a[3] = %d\n",
	   a[0], a[1], a[2], a[3]);

    c = (int *) ((char *) c + 1);
    *c = 500;
    printf("5: a[0] = %d, a[1] = %d, a[2] = %d, a[3] = %d\n",
	   a[0], a[1], a[2], a[3]);

    b = (int *) a + 1;
    c = (int *) ((char *) a + 1);
    printf("6: a = %p, b = %p, c = %p\n", a, b, c);
}

int main(int ac, char **av) {
    f();
    return 0;
}

在QEMU中使用GDB

打开两个终端窗口

在第一个窗口中输入make qemu-gdb

*** Now run 'gdb' in another window. qemu-system-riscv64 -machine virt -bios none -kernel kernel/kernel -m 128M -smp 3 -nographic -drive file=fs.img,if=none,format=raw,id=x0 -device virtio-blk-device,drive=x0,bus=virtio-mmio-bus.0 -S -gdb tcp::25500

在第二个窗口中，修改自己 home 目录下的 .gdbinit 文件，允许 gdb 在xv6-riscv这个目录启动的时候，加载该文件夹下的 .gdbinit 文件。
```
echo "add-auto-load-safe-path YOUR_PATH/xv6-riscv/.gdbinit " >> ~/.gdbinit
```

输入gdb-multiarch

$ echo "add-auto-load-safe-path /home/ubuntu/xv6-riscv/.gdbinit " >> ~/.gdbinit
$ gdb-multiarch                                                                                             
GNU gdb (Ubuntu 9.2-0ubuntu1~20.04) 9.2
Copyright (C) 2020 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.ht
ml>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.
Type "show copying" and "show warranty" for details.
This GDB was configured as "x86_64-linux-gnu".
Type "show configuration" for configuration details.
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.
Find the GDB manual and other documentation resources online at:
    <http://www.gnu.org/software/gdb/documentation/>.

For help, type "help".
Type "apropos word" to search for commands related to "word".
The target architecture is assumed to be riscv:rv64
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
0x0000000000001000 in ?? ()
(gdb)

给代码打断点 简单来说，就是以下几步：

file user/_ls
b main
c
之后就是正常的GDB 使用流程了

FINALLY：

第二个窗口：

(gdb) file user/_ls
Reading symbols from user/_ls...
(gdb) b main
Breakpoint 1 at 0x27a: file user/ls.c, line 75.
(gdb) c
Continuing.
[Switching to Thread 1.3]

Thread 3 hit Breakpoint 1, main (argc=0, argv=0x6c <fmtname+108>)
    at user/ls.c:75
75      {
(gdb)

第一个窗口

(......)
xv6 kernel is booting                                        

hart 1 starting                                                  
hart 2 starting                                                  
init: starting sh                                                
$ ls
(等待 gdb 发送 continue 信号)

之后我们就可以正常地通过 GDB 调试程序啦~

在这里插入图片描述

6.S081环境配置

更好的阅读体验

安装XV6

指针预备知识

在QEMU中使用GDB