Question

我正在远程调试ARM微控制器并尝试在以下代码块中使用gdb修改变量：

for (int i = 0; i < 100; i++) {
    __asm__("nop");
}

当我执行print i时，我可以看到变量的值

(gdb) print i
$1 = 0

执行whatis i会返回此

whatis i
~"type = int\n"

但是当我尝试更改变量时，我得到以下错误

(gdb) set variable i=99
Left operand of assignment is not an lvalue.

我在这里做错了什么？

更新：这里是汇编代码

!        for (int i = 0; i < 100; i++) {
main+38: subs\tr3, #1
main+40: bne.n\t0x80001d0 <main+36>
main+42: b.n\t0x80001c4 <main+24>
main+44: lsrs\tr0, r0, #16
main+46: ands\tr2, r0
!            __asm__("nop");
main+36: nop

Answer 1

我遇到了同样的问题，并使变量volatile有所帮助。

Answer 2

命令只是set i = 99

Answer 3

以这种方式尝试：

(gdb) print i
$1 = 3
(gdb) set var i=6
(gdb) print i
$2 = 6

Answer 4

这里有两个问题，将变量名从i更改为var_i，因为有一些以i开头的set命令，因此set i=6将给出模糊的命令集错误。

“赋值的左操作数不是左值。”可以通过如下所示的代码更改来解决。

volatile int var_i = 1;
  TRACE((2255, 0, NORMAL, "Ravi I am sleeping here........."));
  do
  {
          sleep(5);
          var_i = 1;
  }while(var_i);

(gdb)bt
#1  0x00007f67fd7b9404 in sleep () from /lib64/libc.so.6
#2  0x00000000004cd410 in pgWSNVBUHandleGetUser (warning: Source file is more recent than executable.
ptRequest=<optimized out>, oRequest=<optimized out>,

(gdb) finish
Run till exit from #0  0x00007f67fd7b9550 in __nanosleep_nocancel () from /lib64/libc.so.6
0x00007f67fd7b9404 in sleep () from /lib64/libc.so.6
(gdb) finish
Run till exit from #0  0x00007f67fd7b9404 in sleep () from /lib64/libc.so.6
0x00000000004cd410 in pgWSNVBUHandleGetUser (ptRequest=<optimized out>, oRequest=<optimized out>,
    pptResponse=0x7fff839e8760) at /root/Checkouts/trunk/source/base/webservice/provnvbuuser.c:376
    (gdb)
      │372       volatile int var_i = 1;                                                                                           │
       │373       TRACE((2255, 0, NORMAL, "Ravi I am sleeping here........."));                                            │
       │374       do                                                                                                       │
       │375       {                                                                                                        │
      >│376         sleep(5);                                                                                              │
       │377         var_i = 1;                                                                                             │
       │378       }while(var_i);        

(gdb) set var_i=0
(gdb) n
(gdb) p var_i
$1 = 1
(gdb) set var_i=0
(gdb) p var_i
$2 = 0
(gdb) n
(gdb) n

gdb：“赋值的左操作数不是左值。”

4 个答案: