[MIT6.828] xv6, a simple Unix-like teaching operating system

╰半橙微兮° 2021-10-13 03:43 315阅读 0赞

address: https://pdos.csail.mit.edu/6.828/2018/xv6.html  
book: https://pdos.csail.mit.edu/6.828/2018/xv6/book-rev10.pdf  
git: git clone git://github.com/mit-pdos/xv6-public.git

## xv6 使用gdb调试 ##

1.在xv6顶层目录运行xv6: `make qemu-nox-gdb`  
2.在另一个终端（terminal）运行gdb： `gdb kernel`  
3.在gdb接口，运行 `(gdb) target remote localhost:26000` 26000 是step1运行后给到的端口号  
4.加载用户程序：`(gdb)file user_program`  
5.断点`(gdb) break main`  
6.继续`(gdb) continue`  
7.其它命令  
gdb) info reg  
…  
(gdb) x/24x $esp  
…  
(gdb)

## 常用的一些gdb调试方法 ##

GDB  
See the [GDB manual][] for a full guide to GDB commands. Here are some particularly useful commands for 6.828, some of which don’t typically come up outside of OS development.  
`Ctrl-c`  
Halt the machine and break in to GDB at the current instruction. If QEMU has multiple virtual CPUs, this halts all of them.  
`c (or continue)`  
Continue execution until the next breakpoint or Ctrl-c.  
`si (or stepi)`  
Execute one machine instruction.  
b function or b file:line (or breakpoint)  
Set a breakpoint at the given function or line.  
`b *addr (or breakpoint)`  
Set a breakpoint at the EIP addr.  
`set print pretty`  
Enable pretty-printing of arrays and structs.  
`info registers`  
Print the general purpose registers, eip, eflags, and the segment selectors. For a much more thorough dump of the machine register state, see QEMU’s own info registers command.  
`x/Nx addr`  
Display a hex dump of N words starting at virtual address addr. If N is omitted, it defaults to 1. addr can be any expression.  
`x/Ni addr`  
Display the N assembly instructions starting at addr. Using $eip as addr will display the instructions at the current instruction pointer.  
`symbol-file file`  
(Lab 3+) Switch to symbol file file. When GDB attaches to QEMU, it has no notion of the process boundaries within the virtual machine, so we have to tell it which symbols to use. By default, we configure GDB to use the kernel symbol file, obj/kern/kernel. If the machine is running user code, say hello.c, you can switch to the hello symbol file using symbol-file obj/user/hello.  
QEMU represents each virtual CPU as a thread in GDB, so you can use all of GDB’s thread-related commands to view or manipulate QEMU’s virtual CPUs.  
`thread n`  
GDB focuses on one thread (i.e., CPU) at a time. This command switches that focus to thread n, numbered from zero.  
`info threads`  
List all threads (i.e., CPUs), including their state (active or halted) and what function they’re in.

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gdb调试xv6参考自： https://stackoverflow.com/questions/10534798/debugging-user-code-on-xv6-with-gdb

[GDB manual]: https://sourceware.org/gdb/current/onlinedocs/gdb/