#define _GNU_SOURCE
#include <sched.h>
#include <sys/wait.h>
#include <stdlib.h>
#include <stdio.h>
#include <sys/mman.h>
#include <strings.h>
#include <unistd.h>

#define errExit(msg)    do { perror(msg); exit(EXIT_FAILURE); \
	                               } while (0)
#define STACK_SIZE (1024 * 1024)

int child(void* buf){
	printf("print buf (addr=%p): %s\n",buf,(char *) buf);
	sleep(2);
	printf("print buf (addr=%p): %s\n",buf, (char *)buf);
	exit(EXIT_SUCCESS);
}

int main(){
	char * stack = mmap(NULL,
			STACK_SIZE,
		       	PROT_READ | PROT_WRITE,
			MAP_PRIVATE | MAP_ANONYMOUS | MAP_STACK,
		       	-1,
		       	0);
	if (stack == MAP_FAILED)
		errExit("mmap");
	char * buf = malloc(256 * sizeof(char));
	snprintf(buf,256,"inital"); 
	int pid = clone(child, stack + STACK_SIZE,SIGCHLD | CLONE_THREAD | CLONE_SIGHAND | CLONE_VM, buf);
	if (pid < 0)
		errExit("failed to create child");
	sleep(1);
	snprintf(buf,256,"changed");
	sleep(2);
	exit(EXIT_SUCCESS);
}