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#include <sys/mman.h>
#include <sys/shm.h>
#include <unistd.h>
#include <stdio.h>
int main()
{
int psize = getpagesize();
int id;
void *p;
/*
* We need a shared mapping to enter CF_PARALLEL mode.
* The easiest way to get that is shmat.
*/
id = shmget(IPC_PRIVATE, 2 * psize, IPC_CREAT | 0600);
if (id < 0) {
perror("shmget");
return 2;
}
p = shmat(id, NULL, 0);
if (p == MAP_FAILED) {
perror("shmat");
return 2;
}
/* Protect the second page. */
if (mprotect(p + psize, psize, PROT_NONE) < 0) {
perror("mprotect");
return 2;
}
/*
* Load 4 bytes, 6 bytes from the end of the page.
* On success this will load 0 from the newly allocated shm.
*/
return *(int *)(p + psize - 6);
}
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