c - 调试子进程不适用于 set detach-on-fork off

Question

我有下面的简单程序。

#include <unistd.h>
#include <sys/types.h>
#include <stdio.h>

#define CHILD 0

int main()
{
    pid_t pid;
    printf(" My pid = %d \n", getpid());
    getchar();
    pid = fork();
    if( pid == CHILD){
        printf(" child: My pid = %d \n", getpid());
        while(1);
    }
    else{
        printf(" My pid = %d \n", getpid());
        printf(" Newly created child pid = %d \n", pid);
        while(1);
    }
}

我正在尝试用 gdb 调试它。我想同时调试父进程和子进程。我使用了以下命令

Reading symbols from ./1...done.
(gdb) b 12
Breakpoint 1 at 0x73f: file 1.c, line 12.
(gdb) set detach-on-fork off
(gdb) r
Starting program: ./1 
 My pid = 121710 


Breakpoint 1, main () at 1.c:12
12      pid = fork();
(gdb) n
[New process 121715]
Reading symbols from ./1...done.
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x73f

(gdb) info inferior
  Num  Description       Executable        
* 1    process 121710    ./1 
  2    process 121715    ./1 
(gdb) bt
#0  0x00007ffff7ac8b1c in __libc_fork () at ../sysdeps/nptl/fork.c:135
#1  0x0000555555554744 in main () at 1.c:12
(gdb) n
[New process 121715]
Reading symbols from ./1...done.
Warning:
Cannot insert breakpoint 1.
Cannot access memory at address 0x73f
Cannot insert breakpoint 1.
Cannot access memory at address 0x73f

你们能帮我解决我在上面的 gdb 命令中犯的错误吗？

Answer 1

我在使用 gdb 8.1 调试 fork() 时遇到了同样的问题，调试选项相同。

一种解决方案是在调用 fork() 之前删除所有断点。比如你在fork()的前一个源码行创建了一个断点，用于单步执行fork()，当前inferior停在这个断点后应该删除所有的断点，然后当前inferior可以继续运行成功，不会有错误提示比如不能插入断点……。