Segmentation fault occurs during VFORK execution

1. First of all, understand vfork What is it for ？

Linux Type... On the command line man vfork enter

Look at the instructions in the red box , Which translates to vfork - Create a child process and block the parent process ,block n. block v. Blocking .

The red box below appears at the bottom of the manual BUGS, explain vfork By BUG Of . Translated into The details of signal processing are fuzzy , There are differences between systems ( Different ).BSD The man page indicates :“ To avoid deadlock ,vfork() Never send SIGTTOU( The background process attempts to write a signal from the control terminal ) or SIGTTIN( The background process attempts to read a signal from the control terminal ) The signal ; contrary , Allow output or ioctl, And the input will cause the file end instruction .”

2. appear Segmentation fault The error code is as follows ：

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
int main()
{
    
        pid_t pid=vfork();
        if(pid==-1)
        {
    
                printf("Create process is fault.\n");
        }
        if(pid==0)
        {
    
                printf("Child process %d is running.\n",getpid());
        }
        else
        {
    
                printf("Parent process %d is running.\n",getpid());
        }
        return 0;
}

The results of the program are as follows :

As can be seen from the program results ,vfork Execute subprocess first , Then execute the parent process , But this code appears Segmentation fault.

3. Use strace Command trace this program

stay Linux The input terminal strace -f -s 65500 -i -T ./vfork

From the tracking results, it is only called once exit_group(0), In the right case, it should be executed twice return 0;

How to modify a program ？

#include <stdio.h>
#include <sys/types.h>
#include <unistd.h>
#include <stdlib.h>
int main()
{
    
        pid_t pid=vfork();
        if(pid==-1)
        {
    
                printf("Create process is fault.\n");
        }
        if(pid==0)
        {
    
                printf("Child process %d is running.\n",getpid());
        }
        else
        {
    
                printf("Parent process %d is running.\n",getpid());
        }
        exit(0);// take return 0; To replace the ,exit() Function in stdlib.h Header file 
}

The execution result is :

And it turns out that Segmentation fault The mistake disappeared .