More bytecode ops

src/bytecode.rs

@@ -40,6 +40,7 @@ impl Bytecode {
             0x2C => (Instruction::LoadLocalReference2(), 1),
             0x2D => (Instruction::LoadLocalReference3(), 1),
 
+            0x32 => (Instruction::ArrayElement(), 1),
             0x3B => (Instruction::StoreLocalInt0(), 1),
             0x3C => (Instruction::StoreLocalInt1(), 1),
             0x3D => (Instruction::StoreLocalInt2(), 1),
@@ -59,7 +60,36 @@ impl Bytecode {
 
             0x80 => (Instruction::OrInt(), 1),
 
+            0x99 => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchZero(i16::from_be_bytes(bytes)), 3)
+            }
+            0x9A => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchNonZero(i16::from_be_bytes(bytes)), 3)
+            }
+            0x9B => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchNegative(i16::from_be_bytes(bytes)), 3)
+            }
+            0x9C => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchNonPositive(i16::from_be_bytes(bytes)), 3)
+            }
+            0x9D => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchPositive(i16::from_be_bytes(bytes)), 3)
+            }
+            0x9E => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchNonNegative(i16::from_be_bytes(bytes)), 3)
+            }
+
             0xAC => (Instruction::ReturnInt(), 1),
+            0xA7 => {
+                let bytes = [self.bytes[offset+1], self.bytes[offset+2]];
+                (Instruction::BranchAlways(i16::from_be_bytes(bytes)), 3)
+            }
 
             0xB0 => (Instruction::ReturnReference(), 1),
             0xB1 => (Instruction::ReturnVoid(), 1),
@@ -73,6 +103,7 @@ impl Bytecode {
             0xBA => (Instruction::InvokeDynamic((self.bytes[offset+1] as u16) << 8 | self.bytes[offset+2] as u16, (self.bytes[offset+3] as u16) << 8 | self.bytes[offset+4] as u16), 5),
             0xBB => (Instruction::NewObject((self.bytes[offset+1] as u16) << 8 | self.bytes[offset+2] as u16), 3),
             0xBD => (Instruction::NewArray((self.bytes[offset+1] as u16) << 8 | self.bytes[offset+2] as u16), 3),
+            0xBE => (Instruction::ArrayLength(), 1),
             _ => (Instruction::Unknown(opcode), 1)
         }
     }
@@ -104,68 +135,84 @@ impl Debug for Bytecode {
 #[derive(Debug)]
 #[repr(u8)]
 pub enum Instruction {
-    NoOperation()           = 0x00, // No-Operation
-    StoreIntoIntArray()     = 0x01, // ..., arrayref, index, value
-    PushConstIntM1()        = 0x02, // Push -1
-    PushConstInt0()         = 0x03, // Push 0
-    PushConstInt1()         = 0x04, // Push 1
-    PushConstInt2()         = 0x05, // Push 2
-    PushConstInt3()         = 0x06, // Push 3
-    PushConstInt4()         = 0x07, // Push 4
-    PushConstInt5()         = 0x08, // Push 5
-    PushConstDouble0()      = 0x0E, // Push 0.0
-    PushConstDouble1()      = 0x0F, // Push 1.0
+    NoOperation()               = 0x00, // No-Operation
+    StoreIntoIntArray()         = 0x01, // ..., arrayref, index, value
+    PushConstIntM1()            = 0x02, // Push -1
+    PushConstInt0()             = 0x03, // Push 0
+    PushConstInt1()             = 0x04, // Push 1
+    PushConstInt2()             = 0x05, // Push 2
+    PushConstInt3()             = 0x06, // Push 3
+    PushConstInt4()             = 0x07, // Push 4
+    PushConstInt5()             = 0x08, // Push 5
+    PushConstDouble0()          = 0x0E, // Push 0.0
+    PushConstDouble1()          = 0x0F, // Push 1.0
 
-    LoadByteImmediate(u8)   = 0x10, // push immediate short
-    LoadShortImmediate(u16) = 0x11, // push immediate short
-    LoadConstant(u8)        = 0x12, // Push from constant pool
-    LoadConstant64(u16)     = 0x14, // Push Long or Double from constant pool
-    LoadLocalInt0()         = 0x1A, // Load int from local variable
-    LoadLocalInt1()         = 0x1B, // Load int from local variable
-    LoadLocalInt2()         = 0x1C, // Load int from local variable
-    LoadLocalInt3()         = 0x1D, // Load int from local variable
+    LoadByteImmediate(u8)       = 0x10, // push immediate short
+    LoadShortImmediate(u16)     = 0x11, // push immediate short
+    LoadConstant(u8)            = 0x12, // Push from constant pool
+    LoadConstant64(u16)         = 0x14, // Push Long or Double from constant pool
+    LoadLocalInt0()             = 0x1A, // Load int from local variable
+    LoadLocalInt1()             = 0x1B, // Load int from local variable
+    LoadLocalInt2()             = 0x1C, // Load int from local variable
+    LoadLocalInt3()             = 0x1D, // Load int from local variable
 
-    LoadLocalDouble0()      = 0x26, // Load local double variable reference onto stack
-    LoadLocalDouble1()      = 0x27, // Load local double variable reference onto stack
-    LoadLocalDouble2()      = 0x28, // Load local double variable reference onto stack
-    LoadLocalDouble3()      = 0x29, // Load local double variable reference onto stack
-    LoadLocalReference0()   = 0x2A, // Load local reference variable reference onto stack
-    LoadLocalReference1()   = 0x2B, // Load local reference variable reference onto stack
-    LoadLocalReference2()   = 0x2C, // Load local reference variable reference onto stack
-    LoadLocalReference3()   = 0x2D, // Load local reference variable reference onto stack
+    LoadLocalDouble0()          = 0x26, // Load local double variable reference onto stack
+    LoadLocalDouble1()          = 0x27, // Load local double variable reference onto stack
+    LoadLocalDouble2()          = 0x28, // Load local double variable reference onto stack
+    LoadLocalDouble3()          = 0x29, // Load local double variable reference onto stack
+    LoadLocalReference0()       = 0x2A, // Load local reference variable reference onto stack
+    LoadLocalReference1()       = 0x2B, // Load local reference variable reference onto stack
+    LoadLocalReference2()       = 0x2C, // Load local reference variable reference onto stack
+    LoadLocalReference3()       = 0x2D, // Load local reference variable reference onto stack
 
-    StoreLocalInt0()        = 0x3B, // store int into local variable
-    StoreLocalInt1()        = 0x3C, // store int into local variable
-    StoreLocalInt2()        = 0x3D, // store int into local variable
-    StoreLocalInt3()        = 0x3E, // store int into local variable
-    StoreReference0()       = 0x4B, // store reference into local variable
-    StoreReference1()       = 0x4C, // store reference into local variable
-    StoreReference2()       = 0x4D, // store reference into local variable
-    StoreReference3()       = 0x4E, // store reference into local variable
+    ArrayElement()              = 0x32, // load element from array
+    StoreLocalInt0()            = 0x3B, // store int into local variable
+    StoreLocalInt1()            = 0x3C, // store int into local variable
+    StoreLocalInt2()            = 0x3D, // store int into local variable
+    StoreLocalInt3()            = 0x3E, // store int into local variable
+    StoreReference0()           = 0x4B, // store reference into local variable
+    StoreReference1()           = 0x4C, // store reference into local variable
+    StoreReference2()           = 0x4D, // store reference into local variable
+    StoreReference3()           = 0x4E, // store reference into local variable
 
-    Pop()                   = 0x57, // Pop top stack value
-    Duplicate()             = 0x59, // duplicate top stack value
+    Pop()                       = 0x57, // Pop top stack value
+    Duplicate()                 = 0x59, // duplicate top stack value
 
-    MultiplyInt()           = 0x68, // int multiplication
-    DivideLong()            = 0x6D, // long division
+    MultiplyInt()               = 0x68, // int multiplication
+    DivideLong()                = 0x6D, // long division
 
-    ShiftIntRight()         = 0x7a, // shift int
+    ShiftIntRight()             = 0x7a, // shift int
 
-    OrInt()                 = 0x80, // value, value => or
+    OrInt()                     = 0x80, // value, value => or
 
-    ReturnInt()             = 0xAC, // return integer from function
+    BranchZero(i16)             = 0x99, // branch if value == 0
+    BranchNonZero(i16)          = 0x9A, // branch if value != 0
+    BranchNegative(i16)         = 0x9B, // branch if value <  0
+    BranchNonPositive(i16)      = 0x9C, // branch if value <= 0
+    BranchPositive(i16)         = 0x9D, // branch if value >  0
+    BranchNonNegative(i16)      = 0x9E, // branch if value >= 0
 
-    ReturnReference()       = 0xB0, // return top-ref from current function
-    ReturnVoid()            = 0xB1, // return void from function
-    GetStatic(u16)          = 0xB2, // get static field from class
-    PutStatic(u16)          = 0xB3, // set static field on class
-    GetField(u16)           = 0xB4, // get field from class
-    PutField(u16)           = 0xB5, // set field to a value
-    InvokeVirtual(u16)      = 0xB6, // invoke function on a class
-    InvokeSpecial(u16)      = 0xB7, // invoke instance method
-    InvokeStatic(u16)       = 0xB8, // invoke static function
-    InvokeDynamic(u16, u16) = 0xBA, // invoke dynamic function
-    NewObject(u16)          = 0xBB, // Create a new object from a constant-pool class reference
-    NewArray(u16)           = 0xBD, // Create a new array from a constant-pool component class reference
+    BranchIntEquality(i16)      = 0x9F,
+    BranchIntInequality(i16)    = 0xA0,
+    BranchIntLessThan(i16)      = 0xA1,
+    BranchIntGreaterEquals(i16) = 0xA2,
+    BranchIntGreaterThan(i16)   = 0xA3,
+
+    BranchAlways(i16)           = 0xA7, // branch if true
+    ReturnInt()                 = 0xAC, // return integer from function
+
+    ReturnReference()           = 0xB0, // return top-ref from current function
+    ReturnVoid()                = 0xB1, // return void from function
+    GetStatic(u16)              = 0xB2, // get static field from class
+    PutStatic(u16)              = 0xB3, // set static field on class
+    GetField(u16)               = 0xB4, // get field from class
+    PutField(u16)               = 0xB5, // set field to a value
+    InvokeVirtual(u16)          = 0xB6, // invoke function on a class
+    InvokeSpecial(u16)          = 0xB7, // invoke instance method
+    InvokeStatic(u16)           = 0xB8, // invoke static function
+    InvokeDynamic(u16, u16)     = 0xBA, // invoke dynamic function
+    NewObject(u16)              = 0xBB, // Create a new object from a constant-pool class reference
+    NewArray(u16)               = 0xBD, // Create a new array from a constant-pool component class reference
+    ArrayLength()               = 0xBE, // Get length from array reference
     Unknown(u8),
 }

src/classfile.rs

@@ -786,6 +786,14 @@ impl Into<String> for &AbstractTypeDescription {
 }
 
 impl AbstractTypeDescription {
+    pub fn parse_full(s: &str) -> Result<Self, Error> {
+        let (c, parsed) = Self::parse_first(s)?;
+
+        assert!(c == s.len());
+
+        Ok(parsed)
+    }
+
     pub fn parse_first(s: &str) -> Result<(usize, Self), Error> {
         let mut offset: usize = 0;
         let arrays_parsed = s.trim_start_matches("[");

src/classstore.rs

@@ -168,6 +168,13 @@ impl ClassStore {
         }
     }
 
+    pub fn class_name_from_index(&self, index: usize) -> Option<&String> {
+        return match self.class_file_from_idx(index) {
+            Some(file) => Some(file.get_classname().unwrap()),
+            None => None,
+        }
+    }
+
     pub fn class_file_from_idx(&self, idx: usize) -> Option<&JavaClassFile> {
         return match self.classes.get(idx) {
             Some(entry) => Some(&entry.class_file),

src/heap_area.rs

@@ -200,15 +200,15 @@ impl ObjectArea {
         return class_store.get_native_class_name(native_name_index as usize);
     }
 
-    fn get_object_class_index(&self, reference: ObjectReference) -> usize {
-        match self.get_object(reference) {
+    pub fn get_object_class_index(&self, reference: ObjectReference) -> usize {
+        match self.get_entry(reference) {
             CompartmentEntry::Object(o) => o.class_index,
             _ => unreachable!(),
         }
     }
 
     fn get_reference_class_ref(&self, reference: ObjectReference, class_store: &ClassStore) -> ObjectReference {
-        match self.get_object(reference) {
+        match self.get_entry(reference) {
             CompartmentEntry::Object(o) => class_store.get_class_objectref_from_index(o.class_index),
             CompartmentEntry::Array(a) => a.class_ref,
             _ => unreachable!(),
@@ -230,7 +230,7 @@ impl ObjectArea {
         return ObjectReference(object_index + (DEFAULT_COMPARTMENT_CAPACITY * (compartment_index as u32 + 1)));
     }
 
-    fn get_object(&self, reference: ObjectReference) -> &CompartmentEntry {
+    fn get_entry(&self, reference: ObjectReference) -> &CompartmentEntry {
         let index = reference.0;
         let compartment_index: u32 = (index / DEFAULT_COMPARTMENT_CAPACITY) - 1;
         let object_index: u32      = index % DEFAULT_COMPARTMENT_CAPACITY;
@@ -241,7 +241,7 @@ impl ObjectArea {
         return object;
     }
 
-    fn get_object_mut(&mut self, reference: ObjectReference) -> &mut CompartmentEntry {
+    fn get_entry_mut(&mut self, reference: ObjectReference) -> &mut CompartmentEntry {
         let index = reference.0;
         let compartment_index: u32 = (index / DEFAULT_COMPARTMENT_CAPACITY) - 1;
         let object_index: u32      = index % DEFAULT_COMPARTMENT_CAPACITY;
@@ -252,9 +252,29 @@ impl ObjectArea {
         return object;
     }
 
+    pub fn get_array_length(&self, reference: ObjectReference) -> usize {
+        // TODO: Throw errors
+        let array = match self.get_entry(reference) {
+            CompartmentEntry::Array(a) => a,
+            _ => unreachable!(),
+        };
+
+        array.content.len()
+    }
+
+    pub fn get_array_element(&self, array_ref: ObjectReference, element_index: i32) -> ObjectReference {
+        // TODO: Throw errors
+        let array = match self.get_entry(array_ref) {
+            CompartmentEntry::Array(a) => a,
+            _ => unreachable!(),
+        };
+
+        array.content[element_index as usize]
+    }
+
     pub fn get_object_field(&self, reference: ObjectReference, field_name: &str, accessing_class_idx: usize, class_store: &ClassStore) -> Result<FieldValue, Error> {
         // TODO: Check access rights
-        let object = match self.get_object(reference) {
+        let object = match self.get_entry(reference) {
             CompartmentEntry::Object(o) => o,
             _ => unreachable!(),
         };
@@ -282,7 +302,7 @@ impl ObjectArea {
     }
 
     pub fn set_array_element(&mut self, array_reference: ObjectReference, index: usize, element: ObjectReference) {
-        let array = match self.get_object_mut(array_reference) {
+        let array = match self.get_entry_mut(array_reference) {
             CompartmentEntry::Array(a) => a,
             _ => unreachable!(),
         };
@@ -294,7 +314,7 @@ impl ObjectArea {
 
     pub fn set_object_field(&mut self, reference: ObjectReference, field_name: &str, value: FieldValue, accessing_class_idx: usize, class_store: &ClassStore) -> Result<(), Error> {
         // TODO: Check access rights
-        let object = match self.get_object_mut(reference) {
+        let object = match self.get_entry_mut(reference) {
             CompartmentEntry::Object(o) => o,
             _ => unreachable!(),
         };
@@ -425,6 +445,26 @@ pub struct StaticArea {
 
 impl StaticArea {
 
+    pub fn get(&self, class_name: &String, field_name: &String, expected_field_descriptor: AbstractTypeDescription) -> Result<FieldValue, Error> {
+        // TODO: Access permission checking
+        let static_object = match self.static_objects.get(class_name) {
+            Some(o) => o,
+            None => return Err(Error::RunTimeError(format!("Trying to get '{}.{}' but there is no such static object.", class_name, field_name))),
+        };
+
+        let field_index = match static_object.field_index_from_name(&field_name) {
+            Some(i) => i,
+            None => return Err(Error::RunTimeError(format!("Trying to get '{}.{}' but there is no such static field on this object.", class_name, field_name))),
+        };
+
+        let field_descriptor = &static_object.fields[field_index].descriptor;
+        if expected_field_descriptor != *field_descriptor { 
+            return Err(Error::RunTimeError(format!("Descriptor Mismatch: Trying to get a {expected_field_descriptor:?} from '{class_name}.{field_name} but the field is of type '{field_descriptor:?}'.")));
+        }
+
+        Ok(static_object.fields[field_index].value)
+    }
+
     pub fn set(&mut self, class_name: &String, field_name: &String, field_value: FieldValue) -> Result<(), Error> {
         // TODO: Access permission checking
         let static_object = match self.static_objects.get_mut(class_name) {

src/jvm.rs

@@ -194,7 +194,7 @@ impl JVM {
                     ConstantPoolInfo::NameAndType(ConstantNameAndTypeInfo { name_index: 8, descriptor_index: 9 }),
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: class_name.to_string() }),
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: method_name.to_string() }),
-                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "()V".to_string() }),
+                    ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "([Ljava/lang/String;)V".to_string() }),
                     ConstantPoolInfo::MethodRef(ConstantMethodRefInfo { class_index: 11, name_and_type_index: 13}), // 10
                     ConstantPoolInfo::Class(ConstantClassInfo { name_index: 12 } ),
                     ConstantPoolInfo::Utf8(ConstantUtf8Info { utf8: "java/lang/String".to_string() }),
@@ -227,10 +227,12 @@ impl JVM {
                             attribute_name_index: 3,
                             data: AttributeData::Code(
                                 CodeAttributeData {
-                                    max_stack: 0,
+                                    max_stack: 1,
                                     max_locals: 1,
                                     code: Bytecode {
                                         bytes: Box::new([
+                                            0x2A_u8.to_be(), // aload_0
+
                                             0xB8_u8.to_be(), // invokestatic
                                             0x04_u16.to_be_bytes()[0], // index 4 into the constant
                                             0x04_u16.to_be_bytes()[1], // pool                      
@@ -243,54 +245,12 @@ impl JVM {
                         }
                     ])
                 },
-              MethodInfo {
-                  access_flags: MethodAccessFlagMask { 
-                      mask: MethodAccessFlag::Public.discriminant() | MethodAccessFlag::Static.discriminant()
-                  },
-                  name: "make_arg_string".to_string(),
-                  descriptor: MethodDescriptor {
-                      argument_types: Box::new([]),
-                      return_type: AbstractTypeDescription {
-                          array_level: 0,
-                          kind: AbstractTypeKind::Void(),
-                      }
-                  },
-                  code_attribute_index: 0,
-                  attributes: Box::new([
-                      AttributeInfo {
-                          attribute_name_index: 3,
-                          data: AttributeData::Code(
-                              CodeAttributeData {
-                                  max_stack: 3,
-                                  max_locals: 3,
-                                  code: Bytecode {
-                                      bytes: Box::new([
-                                            0xBB_u8.to_be(), // new
-                                            11_u16.to_be_bytes()[0], // index 11 into the constant
-                                            11_u16.to_be_bytes()[1], // pool                      
-
-                                            0x59_u8.to_be(), // dup
-
-                                            0x2A_u8.to_be(), // aload 0
-
-                                            0xB7_u8.to_be(), // invokespecial
-                                            10_u16.to_be_bytes()[0], // index 10 into the constant
-                                            10_u16.to_be_bytes()[1], // pool                      
-                                      ])
-                                  },
-                                  exception_table: Box::new([]),
-                                  attributes: Box::new([]),
-                              }
-                          )
-                      }
-                  ])
-              }
             ]),
             attributes: Box::new([]),
         };
 
         self.class_store.add_class(entry_class, true)?;                         // 0
-        self.class_store.add_class(JVM::class_native_class_data(), true)?;             // 1
+        self.class_store.add_class(JVM::class_native_class_data(), true)?;      // 1
         self.class_store.load_class(&"java/lang/Object".to_string())?;          // 2
         self.class_store.load_class(&"java/lang/Number".to_string())?;          // 3
         self.class_store.load_class(&"java/lang/Byte".to_string())?;            // 4
@@ -537,13 +497,100 @@ impl JVM {
 
             match instruction {
 
+                Instruction::ArrayLength() => {
+                    let array_reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    let array_length = self.heap_area.object_area.get_array_length(array_reference);
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Int(array_length as i32)))?;
+                },
+
+                Instruction::ArrayElement() => {
+                    let element_index   = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+                    let array_reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    let element = self.heap_area.object_area.get_array_element(array_reference, element_index);
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Reference(element)))?;
+                },
+
+                Instruction::BranchAlways(branch_offset) => {
+                    frame.instruction_pointer -= offset as u32;
+                    frame.instruction_pointer = if branch_offset < 0 { frame.instruction_pointer - branch_offset.abs() as u32} else { frame.instruction_pointer + branch_offset.abs() as u32};
+                }
+
+                Instruction::BranchZero(branch_offset) => {
+                    let test_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                    if test_value == 0 {
+                        frame.instruction_pointer -= offset as u32;
+                        frame.instruction_pointer = if branch_offset < 0 { frame.instruction_pointer - branch_offset.abs() as u32} else { frame.instruction_pointer + branch_offset.abs() as u32};
+                    }
+                }
+
                 Instruction::Duplicate() => {
                     let popped_value = wrap_stackframe_error(class, method, frame.operand_stack.pop_computational_1(0))?;
                     wrap_stackframe_error(class, method, frame.operand_stack.push(popped_value))?;
                     wrap_stackframe_error(class, method, frame.operand_stack.push(popped_value))?;
                 }
 
+                Instruction::GetField(fieldref_index) => {
+                    let (class_name, field_name, field_descriptor) = class.gather_fieldref(fieldref_index).unwrap();
+
+                    let this_object = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    // TODO: Are there any methods callable on arrays?
+                    let this_object_class_index = self.heap_area.object_area.get_object_class_index(this_object);
+                    let this_object_class_name  = self.class_store.class_name_from_index(this_object_class_index).unwrap().to_string();
+                    let this_object_descriptor  = AbstractTypeDescription {
+                        array_level: 0,
+                        kind: AbstractTypeKind::Classname(this_object_class_name.clone())
+                    };
+                    let object_descriptor = AbstractTypeDescription {
+                        array_level: 0,
+                        kind: AbstractTypeKind::Classname(class_name.to_string())
+                    };
+
+                    if ! self.class_store.are_types_compatible(&this_object_descriptor, &object_descriptor) {
+                        return Err(Error::RunTimeError(format!(
+                                    "GetField: Cannot fetch '{field_name}' from class '{class_name}' on instance from class '{}: Types are incompatible'", 
+                                    this_object_class_name  
+                                    )))
+                    }
+
+                    let fetched_value = self.heap_area.object_area.get_object_field(this_object, field_name, frame.class_index, &self.class_store).unwrap();
+
+                    // println!("{fetched_value:?} {field_descriptor}");
+                    // TODO: Check field and value compatability
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push_field_value(fetched_value))?;
+                }
+
+                Instruction::GetStatic(fieldref_index) => {
+                    let (class_name, field_name, field_descriptor) = class.gather_fieldref(fieldref_index).unwrap();
+
+                    if ! self.class_store.have_class(class_name) {
+                        // rewind the bytecode offset, I'll need to execute this instruction again
+                        frame.instruction_pointer -= offset as u32;
+                        return Ok(JVMCallbackOperation::LoadClass(class_name.to_string()));
+                    }
+                    if ! self.class_store.was_init(class_name).unwrap() {
+                        // rewind the bytecode offset, I'll need to execute this instruction again
+                        frame.instruction_pointer -= offset as u32;
+                        return Ok(JVMCallbackOperation::InitClass(class_name.to_string()));
+                    }
+
+                    // TODO: Throw error
+                    let parsed_field_descriptor = AbstractTypeDescription::parse_full(field_descriptor).unwrap();
+
+                    // TODO: Throw error
+                    let fetched_value = self.heap_area.static_area.get(class_name, field_name, parsed_field_descriptor).unwrap();
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push_field_value(fetched_value))?;
+                }
+
                 Instruction::InvokeSpecial(methodref_index) => {
+                    // No instance-based dispatch
                     let (supplied_class_name, supplied_method_name, supplied_descriptor_string) = class.gather_methodref(methodref_index)?;
 
                     if ! self.class_store.have_class(supplied_class_name) {
@@ -654,6 +701,77 @@ impl JVM {
                     return Ok(JVMCallbackOperation::PushFrame(new_frame));
                 },
 
+                Instruction::InvokeVirtual(methodref_index) => {
+                    let (base_class_name, base_method_name, base_descriptor_string) = class.gather_methodref(methodref_index)?;
+
+                    if ! self.class_store.have_class(base_class_name) {
+                        // rewind the bytecode offset, I'll need to execute this instruction again
+                        frame.instruction_pointer -= offset as u32;
+                        return Ok(JVMCallbackOperation::LoadClass(base_class_name.to_string()));
+                    }
+                    if ! self.class_store.was_init(base_class_name).unwrap() {
+                        // rewind the bytecode offset, I'll need to execute this instruction again
+                        frame.instruction_pointer -= offset as u32;
+                        return Ok(JVMCallbackOperation::InitClass(base_class_name.to_string()));
+                    }
+
+                    let base_descriptor = MethodDescriptor::try_from(base_descriptor_string).unwrap();
+
+
+                    // extract arguments, they are on top of the stack
+                    let mut arguments = VecDeque::new();
+                    fill_arguments(class, method, &mut arguments, &base_descriptor.argument_types, &mut frame.operand_stack)?;
+                    let this_object = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+                    arguments.push_front(StackValue::Reference(this_object));
+
+                    // TODO: Are there any methods callable on arrays?
+                    let this_object_class_index = self.heap_area.object_area.get_object_class_index(this_object);
+                    let this_object_class_name  = self.class_store.class_name_from_index(this_object_class_index).unwrap().to_string();
+                    let this_object_descriptor  = AbstractTypeDescription {
+                        array_level: 0,
+                        kind: AbstractTypeKind::Classname(this_object_class_name.clone())
+                    };
+                    let base_object_descriptor = AbstractTypeDescription {
+                        array_level: 0,
+                        kind: AbstractTypeKind::Classname(base_class_name.to_string())
+                    };
+
+
+                    // TODO: Throw error
+                    if ! self.class_store.are_types_compatible(&this_object_descriptor, &base_object_descriptor) {
+                        return Err(Error::RunTimeError(format!(
+                                    "InvokeVirtual: Cannot call '{base_method_name}' from class '{base_class_name}' on instance from class '{}: Types are incompatible'", 
+                                    this_object_class_name  
+                                    )))
+                    }
+
+                    let (invoked_class_index, invoked_method_index, _invoked_method_info) = match ClassMethodIterator::new(this_object_class_index, &self.class_store)
+                        .filter(|(_, _, method_info)| method_info.name       == *base_method_name)
+                        .filter(|(_, _, method_info)| method_info.descriptor == base_descriptor)
+                        .next() 
+                        {
+                            Some(t) => t,
+                            None => {
+                                return Err(Error::RunTimeError(format!(
+                                            "InvokeVirtual: Failed to find requested method '{}' with descriptor '{}' in the type hierarchy of '{}'", 
+                                            base_method_name, 
+                                            base_descriptor_string, 
+                                            this_object_class_name,
+                                        )));
+                            },
+                    };
+
+                    let invoked_class_file = self.class_store.class_file_from_idx(invoked_class_index).unwrap();
+                    let new_frame = StackFrame::new(
+                        invoked_class_file,
+                        invoked_class_index,
+                        invoked_method_index as u16,
+                        arguments.make_contiguous()
+                    );
+
+                    return Ok(JVMCallbackOperation::PushFrame(new_frame));
+                },
+
                 Instruction::LoadByteImmediate(byte) => {
                     // sign extend into int
                     let i8_int = i8::from_be_bytes([byte]);
@@ -681,6 +799,15 @@ impl JVM {
                 Instruction::LoadLocalReference0() => {
                     load_local_reference(class, method, frame, 0)?;
                 }
+                Instruction::LoadLocalReference1() => {
+                    load_local_reference(class, method, frame, 1)?;
+                }
+                Instruction::LoadLocalReference2() => {
+                    load_local_reference(class, method, frame, 2)?;
+                }
+                Instruction::LoadLocalReference3() => {
+                    load_local_reference(class, method, frame, 3)?;
+                }
 
                 Instruction::MultiplyInt() => {
                     let factor_1 = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
@@ -834,12 +961,9 @@ impl JVM {
                 }
 
                 Instruction::ReturnInt() => {
-                    let expected_type = AbstractTypeDescription {
-                        array_level: 0,
-                        kind: AbstractTypeKind::Int(),
-                    };
-                    if method.descriptor.return_type != expected_type {
-                        return Err(Error::OpcodeError(format!("Found opcode '{:?}' on method returning '{:?}'", instruction, method.descriptor.return_type)))
+                    match (method.descriptor.return_type.array_level, &method.descriptor.return_type.kind) {
+                        (_, AbstractTypeKind::Byte() | AbstractTypeKind::Boolean()| AbstractTypeKind::Int() | AbstractTypeKind::Char() | AbstractTypeKind::Short()) => (),
+                        _ => return Err(Error::OpcodeError(format!("Found opcode '{:?}' on method returning '{:?}'", instruction, method.descriptor.return_type)))
                     }
 
                     let int = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
@@ -859,6 +983,13 @@ impl JVM {
                     return Ok(JVMCallbackOperation::PopFrame());
                 },
 
+                Instruction::ShiftIntRight() => {
+                    let shift = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))? as u8 & 0b00011111;
+                    let int   = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
+
+                    wrap_stackframe_error(class, method, frame.operand_stack.push(StackValue::Int(int >> shift)))?;
+                },
+
                 Instruction::StoreLocalInt0() => {
                     let int = wrap_stackframe_error(class, method, frame.operand_stack.pop_int(0))?;
 
@@ -880,6 +1011,27 @@ impl JVM {
                     wrap_stackframe_error(class, method, frame.store_local(3, StackValue::Int(int)))?;
                 },
 
+                Instruction::StoreReference0() => {
+                    let reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    wrap_stackframe_error(class, method, frame.store_local(0, StackValue::Reference(reference)))?;
+                },
+                Instruction::StoreReference1() => {
+                    let reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    wrap_stackframe_error(class, method, frame.store_local(1, StackValue::Reference(reference)))?;
+                },
+                Instruction::StoreReference2() => {
+                    let reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    wrap_stackframe_error(class, method, frame.store_local(2, StackValue::Reference(reference)))?;
+                },
+                Instruction::StoreReference3() => {
+                    let reference = wrap_stackframe_error(class, method, frame.operand_stack.pop_reference(0))?;
+
+                    wrap_stackframe_error(class, method, frame.store_local(3, StackValue::Reference(reference)))?;
+                },
+
                 _ => {
                     return Err(Error::RunTimeError(format!("Opcode not implemented yet: {:?}", instruction)))
                 },

src/main.rs

@@ -20,18 +20,18 @@ fn main() {
     let mut jvm = jvm::JVM::new();
 
     match jvm.entrypoint(
-        &"java/Math".to_string(), 
-        &"v".to_string(),
+        &"Main".to_string(), 
+        &"main".to_string(),
         &["Hello World"],
     ) {
         Ok(()) => (),
         Err(e) => println!("{:#?}", e),
     }
 
-  //  match jvm.run() {
-  //      Ok(()) => (),
-  //      Err(e) => println!("{:#?}", e),
-  //  };
+    match jvm.run() {
+        Ok(()) => (),
+        Err(e) => println!("{:#?}", e),
+    };
 
     //println!("{:#?}", jvm.heap_area.static_area);
 }

src/stackframe.rs

@@ -1,5 +1,5 @@
 use crate::classfile::{ JavaClassFile, AttributeData };
-use crate::heap_area::ObjectReference;
+use crate::heap_area::{ ObjectReference, FieldValue };
 
 #[derive(Copy, Clone, Debug)]
 pub enum StackValue {
@@ -48,6 +48,27 @@ impl OperandStack {
 
         Ok(())
     }
+
+    pub fn push_field_value(&mut self, value: FieldValue) -> Result<(), Error> {
+        match value {
+            FieldValue::Reference(r) => {
+                self.push(StackValue::Reference(r))
+            }
+
+            FieldValue::Boolean(b) => {
+                self.push(StackValue::Int(if b { 1 } else { 0 }))
+            }
+
+            FieldValue::Byte(b) => {
+                self.push(StackValue::Int(b as i32))
+            }
+
+            _ => {
+                println!("{value:?}");
+                todo!();
+            }
+        }
+    }
     
     pub fn pop_computational_1(&mut self, index: usize) -> Result<StackValue, Error> {
         let absolute_index = self.depth as usize - 1 - index;