# 選擇函數堆棧幀 ## 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，當程序暫停后，可以用“`frame n`”命令選擇函數堆棧幀，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); 可以看到程序斷住后，最內層的函數幀為第`0`幀。執行`frame 2`命令后，當前的堆棧幀變成了`fun3`的函數幀。 也可以用“`frame addr`”命令選擇函數堆棧幀，其中`addr`是堆棧地址。仍以上面程序為例： (gdb) frame 2 #2 0x0000000000400586 in func3 (a=10) at test.c:18 18 c = 2 * func2(a); (gdb) i frame Stack level 2, frame at 0x7fffffffe590: rip = 0x400586 in func3 (test.c:18); saved rip = 0x40059e called by frame at 0x7fffffffe5a0, caller of frame at 0x7fffffffe568 source language c. Arglist at 0x7fffffffe580, args: a=10 Locals at 0x7fffffffe580, Previous frame's sp is 0x7fffffffe590 Saved registers: rbp at 0x7fffffffe580, rip at 0x7fffffffe588 (gdb) frame 0x7fffffffe568 #1 0x0000000000400560 in func2 (a=10) at test.c:11 11 c = 2 * func1(a); 使用“`i frame`”命令可以知道`0x7fffffffe568`是`func2`的函數堆棧幀地址，使用“`frame 0x7fffffffe568`”可以切換到`func2`的函數堆棧幀。 參見[gdb手冊](https://sourceware.org/gdb/onlinedocs/gdb/Selection.html#Selection). ## 貢獻者 nanxiao