GDB:为符号的更改分配断点

Question

我正在调试具有分段错误的C应用程序.我已经确定了导致问​​题的变量.但是,我还不知道,当分配变量时会导致分段错误.

如果将新值分配给现有变量,是否有办法在GDB中设置断点？

Answer 1

你需要一个watchpoint:

(gdb) watch my_var

Answer 2

#include <stdio.h>

struct foo {
  int i[12];
  int j;
};

int main(void) {
  struct foo foo = {{0}};
  int *p;

  p = foo.i;
  p[12] = 42;
  printf("j is %d\n", foo.j);
  return 0;
}

gdb ./a.out
[...]
Reading symbols from a.out...done.
(gdb) break main
Breakpoint 1 at 0x40052c: file 6469109.c, line 9.
(gdb) run
Starting program: a.out 

Breakpoint 1, main () at 6469109.c:9
9         struct foo foo = {{0}};
(gdb) watch foo.j
Hardware watchpoint 2: foo.j
(gdb) cont
Continuing.
Hardware watchpoint 2: foo.j

Old value = -7936
New value = 0
0x0000000000400545 in main () at 6469109.c:9
9         struct foo foo = {{0}};
(gdb) cont
Continuing.
Hardware watchpoint 2: foo.j

Old value = 0
New value = 42
main () at 6469109.c:14
14        printf("j is %d\n", foo.j);
(gdb) quit
A debugging session is active.

        Inferior 1 [process 572] will be killed.

Quit anyway? (y or n) y