MIT6.S081 lab3利用gdb调试qemu

在MIT6.S081采用gdb调试qemu的实验中，一开始老出现这样的错误

启动在xv6-lab目录下，开启终端启动GDB调试，弹出警告

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ gdb
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warning: File "/home/hitszfxy/xv6/lab_source/xv6-labs-2020/.gdbinit" auto-loading has been declined by your `auto-load safe-path' set to "$debugdir:$datadir/auto-load".

最后一段，查找相关资料，需要添加修改.gdbinit文件

auto-load safe-path' set to "$debugdir:$datadir/auto-load".

因为.开头的文件，在目录下是隐藏文件，因此需要采用

ls -dl .*

命令查看

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ ls -dl .*
drwxr-xr-x 8 hitszfxy hitszfxy 4096 3月  28 16:44 .
drwxr-xr-x 3 hitszfxy hitszfxy 4096 3月  17 15:41 ..
-rw-r--r-- 1 hitszfxy hitszfxy   86 9月  19  2020 .dir-locals.el
-rw-r--r-- 1 hitszfxy hitszfxy  248 9月  19  2020 .editorconfig
-rw-r--r-- 1 hitszfxy hitszfxy  208 3月  28 16:44 .gdbinit
-rw-r--r-- 1 hitszfxy hitszfxy  130 9月  19  2020 .gdbinit.tmpl-riscv
drwxr-xr-x 8 hitszfxy hitszfxy 4096 9月  19  2020 .git
-rw-r--r-- 1 hitszfxy hitszfxy  195 9月  19  2020 .gitignore

得到以下文件，通过

cat -.gdbinit

指令查看

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ cat .gdbinit
set confirm off
set architecture riscv:rv64
target remote 127.0.0.1:26000
symbol-file kernel/kernel
set disassemble-next-line auto

.gdbinit命令中是否为riscv:rv64，发现是的，无须修改，如果不是的话，可以通过

vi .gdbinit

进入修改，输入i进入编辑界面，编辑完成之后，按下esc，输入：wq保存退出。

然后修改自己 home 目录下的 .gdbinit 文件，允许 gdb 在xv6-labs-2020这个目录启动的时候，加载该文件夹下的 .gdbinit 文件。我这里路径为/home/hitszfxy/xv6/lab_source
/xv6-labs-2020/

echo "add-auto-load-safe-path /home/hitszfxy/xv6/lab_source
/xv6-labs-2020/.gdbinit" >> ~/.gdbinit

目录不同，请按照这里修改

echo "add-auto-load-safe-path "你的路径/.gdbinit" >> ~/.gdbinit

之后启动在/home/hitszfxy/xv6/lab_source/xv6-labs-2020/目录下启动make CPUS=1 qemu-gdb

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ make CPUS=1 qemu-gdb
*** Now run 'gdb' in another window.
qemu-system-riscv64 -machine virt -bios none -kernel kernel/kernel -m 128M -smp 1 -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::26000

端口号为26000

此时在/home/hitszfxy/xv6/lab_source/xv6-labs-2020/目录下重新打开一个终端，输入gdb-multiarch

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ gdb-multiarch

进入gdb调试界面，使用target remote:26000进行连接（target remote : 端口号)

(gdb) target remote:26000
Remote debugging using :26000
warning: No executable has been specified and target does not support
determining executable automatically.  Try using the "file" command.
0x0000000000001000 in ?? ()
=> 0x0000000000001000:	97 02 00 00	auipc	t0,0x0

之后就可以添加断点，开始调试内核启动过程啦！

总结：

1.修改home目录下的.gdbinit文件

echo "add-auto-load-safe-path /home/hitszfxy/xv6/lab_source
/xv6-labs-2020/.gdbinit" >> ~/.gdbinit

2.新建终端1 启动qemu-gdb

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ make CPUS=1 qemu-gdb

3.新建终端2 启动gdb-multiarch，并建立连接,(注意采用gdb-multiarch启动，而不是gdb）

hitszfxy@HItfxy:~/xv6/lab_source/xv6-labs-2020$ gdb-multiarch
(gdb) target remote:26000

4.开始调试