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/* 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) 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;
}
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