x86/cpu-policy: enable build of fuzzing harness by default

... on x86, to make sure its bit-rotting can be limited at least a little.

Since on Ubuntu fread()'s return value needs evaluating, adjust the code
there to also skip the test when there's no data at all.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/fuzz/Makefile

@@ -5,5 +5,7 @@ SUBDIRS-y :=
 SUBDIRS-y += libelf
 SUBDIRS-y += x86_instruction_emulator
 
+SUBDIRS-$(CONFIG_X86_64) += cpu-policy
+
 .PHONY: all clean distclean install uninstall
 all clean distclean install uninstall: %: subdirs-%

tools/fuzz/cpu-policy/afl-policy-fuzzer.c

@@ -133,6 +133,7 @@ int main(int argc, char **argv)
 #endif
     {
         struct cpu_policy *cp = NULL;
+        size_t size;
 
         if ( fp != stdin )
         {
@@ -150,9 +151,9 @@ int main(int argc, char **argv)
         if ( !cp )
             goto skip;
 
-        fread(cp, sizeof(*cp), 1, fp);
+        size = fread(cp, sizeof(*cp), 1, fp);
 
-        if ( !feof(fp) )
+        if ( !size || !feof(fp) )
             goto skip;
 
         check_policy(cp);