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