diff -up diffutils-3.6/src/cmp.c.cmp-s-empty diffutils-3.6/src/cmp.c

--- diffutils-3.6/src/cmp.c.cmp-s-empty	2017-05-18 18:39:59.000000000 +0100

+++ diffutils-3.6/src/cmp.c	2017-05-22 10:53:28.477147864 +0100

@@ -330,12 +330,15 @@ main (int argc, char **argv)

   /* If only a return code is needed,

      and if both input descriptors are associated with plain files,

+     and if both files are larger than 0 bytes (procfs files are always 0),

      conclude that the files differ if they have different sizes

      and if more bytes will be compared than are in the smaller file.  */

   if (comparison_type == type_status

       && S_ISREG (stat_buf[0].st_mode)

-      && S_ISREG (stat_buf[1].st_mode))

+      && S_ISREG (stat_buf[1].st_mode)

+      && stat_buf[0].st_size > 0

+      && stat_buf[1].st_size > 0)

     {

       off_t s0 = stat_buf[0].st_size - file_position (0);

       off_t s1 = stat_buf[1].st_size - file_position (1);