| 1 | #include <sys/mman.h> |
| 2 | #include <sys/shm.h> |
| 3 | #include <unistd.h> |
| 4 | #include <stdio.h> |
| 5 | |
| 6 | int main() |
| 7 | { |
| 8 | int psize = getpagesize(); |
| 9 | int id; |
| 10 | void *p; |
| 11 | |
| 12 | /* |
| 13 | * We need a shared mapping to enter CF_PARALLEL mode. |
| 14 | * The easiest way to get that is shmat. |
| 15 | */ |
| 16 | id = shmget(IPC_PRIVATE, 2 * psize, IPC_CREAT | 0600); |
| 17 | if (id < 0) { |
| 18 | perror("shmget"); |
| 19 | return 2; |
| 20 | } |
| 21 | p = shmat(id, NULL, 0); |
| 22 | if (p == MAP_FAILED) { |
| 23 | perror("shmat"); |
| 24 | return 2; |
| 25 | } |
| 26 | |
| 27 | /* Protect the second page. */ |
| 28 | if (mprotect(p + psize, psize, PROT_NONE) < 0) { |
| 29 | perror("mprotect"); |
| 30 | return 2; |
| 31 | } |
| 32 | |
| 33 | /* |
| 34 | * Load 4 bytes, 6 bytes from the end of the page. |
| 35 | * On success this will load 0 from the newly allocated shm. |
| 36 | */ |
| 37 | return *(int *)(p + psize - 6); |
| 38 | } |