除錯器 gdb 練習

1. gdb 工具 display，執行每一步驟都看變數 b 的值。

   [dywang@dyH gcc]$ gdb -q gdbtest1
   Reading symbols from gdbtest1...done.
   (gdb) l
   1	int main()
   2	{
   3		int a, b, c;
   4		a=5;
   5		b=10;
   6		b+=a;
   7		c=b+a;
   8		return 0;
   9	}
   (gdb) b 2
   Breakpoint 1 at 0x400478: file gdbtest1.c, line 2.
   (gdb) r
   Starting program: gdbtest1 
   
   Breakpoint 1, main () at gdbtest1.c:4
   4		a=5;
   (gdb) display b
   1: b = 0
   (gdb) n
   5		b=10;
   1: b = 0
   (gdb) n
   6		b+=a;
   1: b = 10
   (gdb) n
   7		c=b+a;
   1: b = 15
   (gdb) n
   8		return 0;
   1: b = 15
   (gdb) n
   9	}
   1: b = 15
   (gdb) c
   Continuing.
   
   Program exited normally.
   (gdb) q
   

2. 重新執行 gdb 工具，使用指令 info 查看狀況，目前沒有變數 display，有一個中斷點。

   [dywang@dyH gcc]$ gdb -q gdbtest1
   Reading symbols from gdbtest1...done.
   (gdb) b 2
   Breakpoint 1 at 0x400478: file gdbtest1.c, line 2.
   (gdb) r
   Starting program: gdbtest1 
   
   Breakpoint 1, main () at gdbtest1.c:4
   4		a=5;
   (gdb) info display
   There are no auto-display expressions now.
   (gdb) info break
   Num     Type           Disp Enb Address            What
   1       breakpoint     keep y   0x0000000000400478 in main at gdbtest1.c:2
   	breakpoint already hit 1 time
   

3. 產生變數 a 的 display，並用 info 查看狀況為 enable。

   (gdb) display a 
   1: a = 32767
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   1:   y  a
   

4. disable 變數 a 的 display，再用 info 查看狀況為 disable。

   (gdb) disable display  1
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   1:   n  a
   

5. disable 中斷點 1，再用 info 查看狀況為 disable。

   (gdb) disable break 1
   (gdb) info break
   Num     Type           Disp Enb Address            What
   1       breakpoint     keep n   0x0000000000400478 in main at gdbtest1.c:2
   	breakpoint already hit 1 time
   

6. 增加變數 b 與 c 的 display

   (gdb) display b
   2: b = 0
   (gdb) display c
   3: c = 0
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   3:   y  c
   2:   y  b
   1:   n  a
   

7. enable 變數 a 的 display

   (gdb) enable display  1
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   3:   y  c
   2:   y  b
   1:   y  a
   

8. 繼續下一步， a, b, c 三個變數的值皆 display

   (gdb) n
   5		b=10;
   3: c = 0
   2: b = 0
   1: a = 5
   

9. delete 變數的 display

   (gdb) delete display 1
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   3:   y  c
   2:   y  b
   (gdb) delete display 2
   (gdb) info display
   Auto-display expressions now in effect:
   Num Enb Expression
   3:   y  c