diff -up diffutils-3.10/src/cmp.c.orig diffutils-3.10/src/cmp.c
--- diffutils-3.10/src/cmp.c.orig	2024-07-23 12:27:16.243455513 +0200
+++ diffutils-3.10/src/cmp.c	2024-07-23 12:31:55.560196269 +0200
@@ -343,12 +343,13 @@ 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
-      && 0 <= stat_buf[0].st_size && S_ISREG (stat_buf[0].st_mode)
-      && 0 <= stat_buf[1].st_size && S_ISREG (stat_buf[1].st_mode))
+      && 0 < stat_buf[0].st_size && S_ISREG (stat_buf[0].st_mode)
+      && 0 < stat_buf[1].st_size && S_ISREG (stat_buf[1].st_mode))
     {
       off_t s0 = stat_buf[0].st_size - file_position (0);
       off_t s1 = stat_buf[1].st_size - file_position (1);