操作系统-xv6-debug方法

xv6 debug基本方法

Debug

• 参考

调试kernel代码

Console

• .gdbinit

  1 set confirm off
  2 set architecture riscv:rv64
  3 target remote 127.0.0.1:26000
  4 symbol-file kernel/kernel
  5 set disassemble-next-line auto
  6 set riscv use-compressed-breakpoints yes

• make qemu-gdb : 开启gdb server
• gdb-multiarch : 连接gdb server

• 

VsCode

• .gdbinit

  1 set confirm off
  2 set architecture riscv:rv64
  3 # target remote 127.0.0.1:26000
  4 symbol-file kernel/kernel
  5 # symbol-file user/_ls
  6 set disassemble-next-line auto
  7 set riscv use-compressed-breakpoints yes

• terminal : make qemu-gdb CPUs=1
• debug console : attach to gdbServer

• 

• 

调试user代码

Console

• .gdbinit

  1 set confirm off
  2 set architecture riscv:rv64
  3 target remote 127.0.0.1:26000
  4 # symbol-file kernel/kernel
  5 symbol-file user/_ls
  6 set disassemble-next-line auto
  7 set riscv use-compressed-breakpoints yes

• 

VsCode

• Step1: terminal : make qemu-gdb。
• Step2: 点击左侧按钮运行与调试，并点击左上角绿色三角（Attach to gdb)
• Step3 : debug console : interrupt
• Step5 : debug console : b *0x27a，即将断点置于ls程序入口
• Step6 : debug console : file user/_ls。加载ls的调试符号 ; then continue
• Step7 : terminal : (运行应用程序)ls
• debug console

  Reading symbols from /home/shc/OSLab/xv6-labs-2020/kernel/kernel...
  The target architecture is assumed to be riscv:rv64
  0x0000000000001000 in ?? ()
  => 0x0000000000001000:	97 02 00 00	auipc	t0,0x0
  **interrupt**
  Thread 1 received signal SIGINT, Interrupt. scheduler () at kernel/proc.c:465 \n 465	    intr_on();
  **b *0x27a**
  Breakpoint 1 at 0x27a
  **file user/_ls**
  Reading symbols from user/_ls...
  **c**
  Continuing.
  Thread 2 hit Breakpoint 1, main (argc=0, argv=0x6c <fmtname+108>) at user/ls.c:75
  75	{

  通过readelf确认应用程序入口点
  

调试系统调用 kernel -> user -> kernel

• step1 : gdb client 连接 gdb server，一开始是kenrel。

• step2 : 加载user文件,打断点

  • file user/_ls ; break [line at user program使用的system call]

  • 

• step3 : break point at (你想要调试的系统调用)(这里时fstat syscall); and then breakpoint at ecall

  • bug : 按理来说这时候page table应该是user的page table，不知道为什么这里时kernel的page table ?
  • b 38 ; b [at ecall] (ecall的语义类似于x86-64的syscall)

    
    

• step4 : 进入trampoline (进入kenrel前的最后阶段)

  • break at start of trampoline

    
    

  • break at end of trampoline

    

    • 如何知道trampoline最后jr t0的addr是0x3ffffff08e？
      • x/40i $pc显示当前PC后面的40条汇编

  • si从trampoline中出来。进入kernel的usertrap

    • 记得file kernel/kernel 因为现在要调试kernel

      

• step5: 成功进入kernel，接下来就是正常的调试 kernel的C code