Initial FENCE implementation

src/instructions.rs

@@ -112,6 +112,16 @@ pub(crate) fn find_and_exec(instr: Instruction, core: &mut Core) -> Result<(), E
                 Err(IllegalInstruction)
             }
         }
+        0b00011 => match instr.funct3() {
+            // MISC_MEM
+            0b000 => {
+                // FENCE is just implemented as a SeqCst fence always here
+                // I dont yet care about the potential performance issue this may bring
+                std::sync::atomic::fence(std::sync::atomic::Ordering::SeqCst);
+                Ok(())
+            }
+            _ => Err(IllegalInstruction),
+        },
         _ => Err(IllegalInstruction),
     }
 }