可以在gdb中检查函数的返回值吗?假设返回值是,而不是赋值给变量的?
发布于 2008-11-06 05:01:15
我想有更好的方法可以做到这一点,但是finish命令会一直执行,直到当前堆栈帧被弹出并打印出返回值--给定程序
int fun() {
return 42;
}
int main( int argc, char *v[] ) {
fun();
return 0;
}
你可以这样调试它--
(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
。不要使用frame
命令的缩写f
!
发布于 2008-11-06 04:57:28
可以,只需输入print $eax
即可检查EAX
寄存器。对于大多数函数,返回值存储在该寄存器中,即使它不被使用。
例外情况是返回大于32位的类型的函数,特别是64位整数(long long
)、double
和structs
或classes
。
另一个例外是如果您不是在英特尔架构上运行。在这种情况下,您必须确定使用了哪个寄存器(如果有的话)。
发布于 2009-07-14 02:05:06
下面是如何在没有符号的情况下做到这一点。
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,注意使用"info frame“来检查帧,使用"frame #”将上下文导航到另一个上下文(在堆栈中上下移动)
bt还展示了一个缩写的堆栈来帮助解决问题。
https://stackoverflow.com/questions/267674
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