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Created Jan 10, 2018
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Map physical memory from /dev/mem to user space and print value of memroy location specified in command line
#include <cinttypes>
#include <stdio.h>
#include <stdlib.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <unistd.h>
int main(int argc, char *argv[]) {
if (argc < 3) {
printf("Usage: %s <phys_addr> <offset>\n", argv[0]);
return 0;
off_t offset = strtoul(argv[1], NULL, 0);
size_t len = strtoul(argv[2], NULL, 0);
// Truncate offset to a multiple of the page size, or mmap will fail.
size_t pagesize = sysconf(_SC_PAGE_SIZE);
off_t page_base = (offset / pagesize) * pagesize;
off_t page_offset = offset - page_base;
int fd = open("/dev/iomem", O_SYNC);
uint8_t* mem = static_cast<uint8_t*>(mmap(NULL, page_offset + len, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, page_base));
if (mem == MAP_FAILED) {
perror("Can't map memory");
return -1;
size_t i;
for (i = 0; i < len; ++i)
printf("%02x ", (int)mem[page_offset + i]);
return 0;
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