向上或向下切换函数堆栈帧

#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调试程序时，当程序暂停后，可以用“up n”或“down n”命令向上或向下选择函数堆栈帧，其中n是层数。以上面程序为例：

(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);

可以看到程序断住后，先执行“frame 2”命令，切换到fun3函数。接着执行“up 1”命令，此时会切换到main函数，也就是会往外层的堆栈帧移动一层。反之，当执行“down 2”命令后，又会向内层堆栈帧移动二层。如果不指定n，则n默认为1.

还有“up-silently n”和“down-silently n”这两个命令，与“up n”和“down n”命令区别在于，切换堆栈帧后，不会打印信息，仍以上面程序为例：

(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

可以看到从func3切换到main函数堆栈帧时，并没有打印出相关信息。

参见 gdb手册.