| 1 | #include <sys/mman.h> |
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| 2 | #include <signal.h> |
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| 3 | #include <stdio.h> |
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| 4 | #include <unistd.h> |
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| 5 | |
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| 6 | enum { |
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| 7 | kMmapSize = 0x1000, |
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| 8 | kMagicValue = 47, |
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| 9 | }; |
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| 10 | |
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| 11 | void *address; |
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| 12 | volatile sig_atomic_t signaled = 0; |
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| 13 | |
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| 14 | void handler(int sig) |
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| 15 | { |
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| 16 | signaled = 1; |
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| 17 | if (munmap(addr: address, len: kMmapSize) != 0) |
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| 18 | { |
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| 19 | perror(s: "munmap" ); |
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| 20 | _exit(status: 5); |
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| 21 | } |
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| 22 | |
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| 23 | void* newaddr = mmap(addr: address, len: kMmapSize, PROT_READ | PROT_WRITE, |
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| 24 | MAP_ANON | MAP_FIXED | MAP_PRIVATE, fd: -1, offset: 0); |
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| 25 | if (newaddr != address) |
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| 26 | { |
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| 27 | fprintf(stderr, format: "Newly mmaped address (%p) does not equal old address (%p).\n" , |
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| 28 | newaddr, address); |
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| 29 | _exit(status: 6); |
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| 30 | } |
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| 31 | *(int*)newaddr = kMagicValue; |
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| 32 | } |
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| 33 | |
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| 34 | int main() |
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| 35 | { |
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| 36 | if (signal(SIGSEGV, handler: handler) == SIG_ERR) |
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| 37 | { |
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| 38 | perror(s: "signal" ); |
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| 39 | return 1; |
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| 40 | } |
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| 41 | |
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| 42 | address = mmap(NULL, len: kMmapSize, PROT_NONE, MAP_ANON | MAP_PRIVATE, fd: -1, offset: 0); |
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| 43 | if (address == MAP_FAILED) |
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| 44 | { |
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| 45 | perror(s: "mmap" ); |
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| 46 | return 2; |
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| 47 | } |
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| 48 | |
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| 49 | // This should first trigger a segfault. Our handler will make the memory readable and write |
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| 50 | // the magic value into memory. |
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| 51 | if (*(int*)address != kMagicValue) |
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| 52 | return 3; |
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| 53 | |
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| 54 | if (! signaled) |
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| 55 | return 4; |
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| 56 | |
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| 57 | return 0; |
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| 58 | } |
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| 59 | |
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