/* When trying to map /dev/mem with offset 0xFFFFF000 on the ARM platform, mmap * returns -EOVERFLOW. * * Since off_t is defined as a long int and the sign bit is set in the address, * the shift operation shifts in ones instead of zeroes * from the left. This results the offset sent to the kernel function becomes * 0xFFFFFFFF instead of 0x000FFFFF with MMAP2_PAGE_SHIFT set to 12. */ #include <unistd.h> #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <fcntl.h> #include <sys/mman.h> #define FATAL do { fprintf(stderr, "Error at line %d, file %s (%d) [%s]\n", \ __LINE__, __FILE__, errno, strerror(errno)); exit(1); } while(0) #define MAP_SIZE 4096UL #define MAP_MASK (MAP_SIZE - 1) int main(int argc, char **argv) { void* map_base = 0; int fd; off_t target = 0xfffff000; if((fd = open("/dev/mem", O_RDWR | O_SYNC)) == -1) { /* skip test for non-root users */ if (errno == EACCES) return 0; FATAL; } printf("/dev/mem opened.\n"); fflush(stdout); /* Map one page */ map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, fd, target & ~MAP_MASK); if(map_base == (void *) -1) FATAL; printf("Memory mapped at address %p.\n", map_base); fflush(stdout); if(munmap(map_base, MAP_SIZE) == -1) FATAL; close(fd); return 0; }