Question

假设返回值不分配给变量，是否可以检查gdb中函数的返回值？

Answer 1

我想有更好的方法可以做到，但是finish命令会执行，直到当前的堆栈帧弹出并打印返回值 - 给定程序

int fun() {
    return 42;
}

int main( int argc, char *v[] ) {
    fun();
    return 0;
}

你可以这样调试 -

(gdb) r
Starting program: /usr/home/hark/a.out 

Breakpoint 1, fun () at test.c:2
2               return 42;
(gdb) finish
Run till exit from #0  fun () at test.c:2
main () at test.c:7
7               return 0;
Value returned is $1 = 42
(gdb)

finish命令可以缩写为fin。请勿使用f，它是frame命令的缩写！

Answer 2

是的，只需输入EAX来检查print $eax注册表。对于大多数函数，返回值存储在该寄存器中，即使它未被使用。

对此的例外是函数返回大于32位的类型，特别是64位整数（long long），double和structs或classes。< / p>

另一个例外是如果您没有在英特尔架构上运行。在这种情况下，您必须确定使用哪个寄存器，如果有的话。

Answer 3

这是没有符号的todo。

gdb ls
This GDB was configured as "ppc64-yellowdog-linux-gnu"...
(no debugging symbols found)
Using host libthread_db library "/lib64/libthread_db.so.1".

(gdb) break __libc_start_main
Breakpoint 1 at 0x10013cb0
(gdb) r
Starting program: /bin/ls
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
Breakpoint 1 at 0xfdfed3c
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread 4160418656 (LWP 10650)]
(no debugging symbols found)
(no debugging symbols found)
[Switching to Thread 4160418656 (LWP 10650)]

Breakpoint 1, 0x0fdfed3c in __libc_start_main () from /lib/libc.so.6
(gdb) info frame
Stack level 0, frame at 0xffd719a0:
 pc = 0xfdfed3c in __libc_start_main; saved pc 0x0
 called by frame at 0x0
 Arglist at 0xffd71970, args:
 Locals at 0xffd71970, Previous frame's sp is 0xffd719a0
 Saved registers:
  r24 at 0xffd71980, r25 at 0xffd71984, r26 at 0xffd71988, r27 at 0xffd7198c,
  r28 at 0xffd71990, r29 at 0xffd71994, r30 at 0xffd71998, r31 at 0xffd7199c,
  pc at 0xffd719a4, lr at 0xffd719a4
(gdb) frame 0
#0  0x0fdfed3c in __libc_start_main () from /lib/libc.so.6
(gdb) info fr
Stack level 0, frame at 0xffd719a0:
 pc = 0xfdfed3c in __libc_start_main; saved pc 0x0
 called by frame at 0x0
 Arglist at 0xffd71970, args:
 Locals at 0xffd71970, Previous frame's sp is 0xffd719a0
 Saved registers:
  r24 at 0xffd71980, r25 at 0xffd71984, r26 at 0xffd71988, r27 at 0xffd7198c,
  r28 at 0xffd71990, r29 at 0xffd71994, r30 at 0xffd71998, r31 at 0xffd7199c,
  pc at 0xffd719a4, lr at 0xffd719a4

格式化有点混乱，请注意使用“info frame”检查帧，并使用“frame＃”将您的上下文导航到另一个上下文（堆栈上下）

bt还显示了一个缩写堆栈来帮助。

如何在GDB中检查函数的返回值？

3 个答案: