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#include <sys/mman.h>
#include <signal.h>
#include <stdio.h>
#include <unistd.h>
enum {
kMmapSize = 0x1000,
kMagicValue = 47,
};
void *address;
volatile sig_atomic_t signaled = 0;
void handler(int sig)
{
signaled = 1;
if (munmap(address, kMmapSize) != 0)
{
perror("munmap");
_exit(5);
}
void* newaddr = mmap(address, kMmapSize, PROT_READ | PROT_WRITE,
MAP_ANON | MAP_FIXED | MAP_PRIVATE, -1, 0);
if (newaddr != address)
{
fprintf(stderr, "Newly mmaped address (%p) does not equal old address (%p).\n",
newaddr, address);
_exit(6);
}
*(int*)newaddr = kMagicValue;
}
int main()
{
if (signal(SIGSEGV, handler) == SIG_ERR)
{
perror("signal");
return 1;
}
address = mmap(NULL, kMmapSize, PROT_NONE, MAP_ANON | MAP_PRIVATE, -1, 0);
if (address == MAP_FAILED)
{
perror("mmap");
return 2;
}
// This should first trigger a segfault. Our handler will make the memory readable and write
// the magic value into memory.
if (*(int*)address != kMagicValue)
return 3;
if (! signaled)
return 4;
return 0;
}
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