What causes a segmentation fault on a call to inb_p()?

Question

I am getting a segmentation fault when trying to read a port with inb_p( ). I\'m compiling this on a Debian system running 2.6.6 kernel on an Intel D525 dual-core system (Ad

Answer 1

I found the problem. The call to inb_p() requires access to port 0x80 in addition to the port to be read.

Apparently, when I tried iopl(), I didn't call it correctly, because that should have worked.

The following code eliminated the segfault:

  /* Get access to the ports */
  if (ioperm(0x80, 1, 1)) 
  {
     perror("ioperm");
     exit(EXIT_FAILURE);
  }
  if (ioperm(BASEPORT+DIPSWITCH, 10, 1)) 
  {
     perror("ioperm");
     exit(EXIT_FAILURE);
  }