In elfutils 0.124, libdwfl's compare_modules routine screws up for
x86_64.  The problem is that the kernel pseudo-module's address gets
compared incorrectly to module addresses, and is consequently not
correctly sorted in the dwfl->modules array.

The following simpler implementation works and explains:

static int
compare_modules (const void *a, const void *b)
{
  Dwfl_Module *const *p1 = a, *const *p2 = b;
  const Dwfl_Module *m1 = *p1, *m2 = *p2;
  if (m1 == NULL)
    return -1;
  if (m2 == NULL)
    return 1;

  // NB: Computing a signed difference between m1-> and m2-> is not
  // good enough, since the possible range of the difference exceeds
  // the representational limits of signed numbers of the same
  // bit-width.
  //
  // e.g: take 8-bit values.
  // m1=255 m2=0 => m1 larger, should return 1, but (signed char) (255-0) = -1 !

  if (m1->low_addr < m2->low_addr)
    return -1;
  else if (m1->low_addr > m2->low_addr)
    return 1;
  else
    return 0;
}