Segmentation fault (core dumped) when using clone() system call

[binladenvn88]

I'm trying write small test code using clone() system call.

/*
 * test.c
 */
#include <stdio.h>
#include <stdlib.h>
#include <linux/sched.h>

struct shared_data_struct {
        unsigned int data1;
        unsigned int data2;
};

struct shared_data_struct shared_data;

static int inc_second(struct shared_data_struct *);

int main(){

        int i, j, pid;
        void *child_stack;

        /* allocate memory for other process to execute in */
        if((child_stack = (void *) malloc(4096)) == NULL) {
                perror("Cannot allocate stack for child");
                exit(1);
        }

        /* clone process and run in the same memory space */
        if ((pid = clone((void *)&inc_second, child_stack,
                        CLONE_VM, &shared_data)) < 0) {
                perror("clone called failed.");
                exit(1);
        }

        /* increment first member of shared struct */
        for (j = 0; j < 2000; j++) {
                for (i = 0; i < 100000; i++) {
                        shared_data.data1++;
                }
        }

        return 0;
}

int inc_second(struct shared_data_struct *sd)
{
        int i,j;

        /* increment second member of shared struct */
        for (j = 1; j < 2000; j++) {
                for (i = 1; i < 100000; i++) {
                        sd->data2++;
                }
        }
}

Compile above source code has not any warning or error.

$ gcc -o test test.c

But, when i run this program, i have gotten error message:

Segmentation fault (core dumped)

I really don't know why have this error?
Please suggest for me solve this problem.
Thank so much!

[kbw]

Shortcuts cost time.

#include <stdio.h>
#include <stdlib.h>
#include <linux/sched.h>

struct shared_data_struct
{
	unsigned long data1;
	unsigned long data2;
};

struct shared_data_struct shared_data;

static int inc_second(struct shared_data_struct *);

int main()
{
	int i, j, pid;
	void *child_stack;

	/* allocate memory for other process to execute in */
	child_stack = (void *) malloc(4096);
	if (child_stack == NULL)
	{
		perror("Cannot allocate stack for child");
		exit(1);
	}

	/* clone process and run in the same memory space */
	pid = clone((void *)&inc_second, child_stack, CLONE_VM, &shared_data);
	if (pid < 0)
	{
		perror("clone called failed.");
		exit(1);
	}

	/* increment first member of shared struct */
	for (j = 0; j < 2000; ++j)
		for (i = 0; i < 100000; ++i)
			++shared_data.data1;

	sleep(10);	/* let things settle down */
	printf("%lu %lu\n", shared_data.data1, shared_data.data2);

	return 0;
}

int inc_second(struct shared_data_struct *sd)
{
	int i,j;

	/* increment second member of shared struct */
	for (j = 1; j < 2000; ++j)
		for (i = 1; i < 100000; ++i)
			++(sd->data2);
}

[binladenvn88]

Thank you for reply, but perhap have some thing wrong. After compile above source code of you successfully, i have gotten same error "Segmentation fault (core dumped)" when run program.
I'm running on Ubuntu 12.04, gcc (Ubuntu/Linaro 4.6.3-1ubuntu5) 4.6.3
Could you have suggest for me to solve this problem,
Thank you so much!

[kbw]

Mine runs ok (using an up to date ArchLinux), both in and outside of gdb. I'll take another look when I get onto a Linux box.

[binladenvn88]

Thank you, but my program require run on Ubuntu or Debian, and now i can't found error anywhere, ^_^,

[kbw]

You may find this article useful.
http://www.linuxjournal.com/article/5211?page=0,0