向上或向下切換函數堆棧幀

例子

#include <stdio.h>

int func1(int a)
{
        return 2 * a;
}

int func2(int a)
{
        int c = 0;
        c = 2 * func1(a);
        return c;
}

int func3(int a)
{
        int c = 0;
        c = 2 * func2(a);
        return c;
}

int main(void)
{
        printf("%d\n", func3(10));
        return 0;
}

技巧

用gdb調試程序時，當程序暫停後，可以用“up n”或“down n”命令向上或向下選擇函數堆棧幀，其中n是層數。以上面程序為例：

(gdb) b test.c:5
Breakpoint 1 at 0x40053d: file test.c, line 5.
(gdb) r
Starting program: /home/nanxiao/test

Breakpoint 1, func1 (a=10) at test.c:5
5               return 2 * a;
(gdb) bt
#0  func1 (a=10) at test.c:5
#1  0x0000000000400560 in func2 (a=10) at test.c:11
#2  0x0000000000400586 in func3 (a=10) at test.c:18
#3  0x000000000040059e in main () at test.c:24
(gdb) frame 2
#2  0x0000000000400586 in func3 (a=10) at test.c:18
18              c = 2 * func2(a);
(gdb) up 1
#3  0x000000000040059e in main () at test.c:24
24              printf("%d\n", func3(10));
(gdb) down 2
#1  0x0000000000400560 in func2 (a=10) at test.c:11
11              c = 2 * func1(a);

可以看到程序斷住後，先執行“frame 2”命令，切換到fun3函數。接著執行“up 1”命令，此時會切換到main函數，也就是會往外層的堆棧幀移動一層。反之，當執行“down 2”命令後，又會向內層堆棧幀移動二層。如果不指定n，則n默認為1.

還有“up-silently n”和“down-silently n”這兩個命令，與“up n”和“down n”命令區別在於，切換堆棧幀後，不會打印信息，仍以上面程序為例：

(gdb) up
#2  0x0000000000400586 in func3 (a=10) at test.c:18
18              c = 2 * func2(a);
(gdb) bt
#0  func1 (a=10) at test.c:5
#1  0x0000000000400560 in func2 (a=10) at test.c:11
#2  0x0000000000400586 in func3 (a=10) at test.c:18
#3  0x000000000040059e in main () at test.c:24
(gdb) up-silently
(gdb) i frame
Stack level 3, frame at 0x7fffffffe5a0:
 rip = 0x40059e in main (test.c:24); saved rip = 0x7ffff7a35ec5
 caller of frame at 0x7fffffffe590
 source language c.
 Arglist at 0x7fffffffe590, args:
 Locals at 0x7fffffffe590, Previous frame's sp is 0x7fffffffe5a0
 Saved registers:
  rbp at 0x7fffffffe590, rip at 0x7fffffffe598

可以看到從func3切換到main函數堆棧幀時，並沒有打印出相關信息。

參見gdb手冊.

貢獻者

nanxiao