Update calling conventions.

src/bin/dvm/main.rs

@@ -1,7 +1,7 @@
 use deimos::object_file::{DvmObjectFile, DvmPath};
 use deimos::vm::constant::DvmConstant;
 use deimos::vm::function::DvmFunction;
-use deimos::vm::instruction::{Immediate, Instruction, Location};
+use deimos::vm::instruction::{Immediate, Instruction};
 use deimos::vm::platform::get_std_lib_platform_functions;
 use deimos::vm::source_code_location::SourceCodeLocation;
 use deimos::vm::{dump_state, run_main_function, DvmContext, DvmState};
@@ -16,16 +16,23 @@ fn main() {
     //
     // fn main() {
     //     println "Hello, World!"
+    //     println foo()
     // }
+    //
+    // fn foo() = 42
     let mut greeter_object_file = DvmObjectFile::new(DvmPath::new("greeter", "greeter.dmo"));
 
+    use Instruction::*;
     let main_instructions = vec![
-        Instruction::MoveImmediate {
+        MoveImmediate {
-            destination: Location::Register(0),
+            destination_register: 0,
             immediate: Immediate::Constant(DvmConstant::String(String::from("Hello, World!"))),
         },
-        Instruction::Push { source_register: 0 },
+        // prepare for call to println
-        Instruction::InvokeStaticPlatform {
+        Push { source_register: 0 }, // save r0
+        Push { source_register: 0 }, // arg0
+        // call
+        InvokeStaticPlatform {
             function_name: Rc::new(String::from("std::core::println")),
             source_code_location: SourceCodeLocation {
                 source_file_name: String::from("greeter.dm"),
@@ -33,20 +40,55 @@ fn main() {
                 char: 5,
             },
         },
-        Instruction::Pop {
+        // unwind from call
-            // println return value
+        Pop {
             destination_register: None,
+        }, // arg0
+        Pop {
+            destination_register: Some(0), // restore r0
         },
-        Instruction::Pop {
+        // prepare for call to foo
-            // arg0 to println
+        Push { source_register: 0 }, // save r0
+        InvokeStatic {
+            function_name: Rc::new(String::from("greeter::foo")),
+            source_code_location: SourceCodeLocation {
+                source_file_name: String::from("greeter.dm"),
+                line: 5,
+                char: 13,
+            },
+        },
+        Pop { destination_register: Some(0) }, // restore r0
+        TakeReturnValue {
+            destination_register: 1,
+        },
+        // call println again
+        Push { source_register: 1 }, // save r1
+        Push { source_register: 0 }, // save r0
+        Push { source_register: 1 }, // arg0
+        InvokeStaticPlatform {
+            function_name: Rc::new(String::from("std::core::println")),
+            source_code_location: SourceCodeLocation {
+                source_file_name: String::from("greeter.dm"),
+                line: 5,
+                char: 5,
+            },
+        },
+        Pop {
             destination_register: None,
+        }, // arg0
+        Pop {
+            destination_register: Some(0), // restore r0
         },
-        Instruction::MoveImmediate {
+        Pop {
-            destination: Location::Register(1),
+            destination_register: Some(1), // restore r1
+        },
+        // return 0
+        MoveImmediate {
+            destination_register: 2,
             immediate: Immediate::Int(0),
         },
-        Instruction::Push { source_register: 1 },
+        SetReturnValue { source_register: 2 },
-        Instruction::Return,
+        Return, // explicit, not needed
     ];
 
     let main_function = DvmFunction::new(
@@ -59,14 +101,32 @@ fn main() {
         },
     );
 
+    let foo_function_instructions = vec![
+        MoveImmediate {
+            destination_register: 0,
+            immediate: Immediate::Int(42),
+        },
+        SetReturnValue { source_register: 0 },
+        Return, // explicit, not needed
+    ];
+
+    let foo_function = DvmFunction::new(
+        "greeter::foo",
+        &foo_function_instructions,
+        SourceCodeLocation {
+            source_file_name: String::from("greeter.dm"),
+            line: 8,
+            char: 1,
+        },
+    );
+
     greeter_object_file.add_function(main_function);
+    greeter_object_file.add_function(foo_function);
 
     let mut state = DvmState::new();
     let mut context = DvmContext::new("greeter::main");
     context.add_platform_functions(get_std_lib_platform_functions());
-    greeter_object_file.load_to_context(&mut context, &|path| {
+    greeter_object_file.load_to_context(&mut context, &|path| todo!());
-        todo!()
-    });
 
     let exit_code = run_main_function(&mut state, &context);
 

src/vm/instruction.rs

@@ -5,7 +5,7 @@ use std::rc::Rc;
 #[derive(Debug, Clone)]
 pub enum Instruction {
     MoveImmediate {
-        destination: Location,
+        destination_register: usize,
         immediate: Immediate,
     },
     Copy {
@@ -40,6 +40,12 @@ pub enum Instruction {
         function_name: Rc<String>,
         source_code_location: SourceCodeLocation,
     },
+    SetReturnValue {
+        source_register: usize,
+    },
+    TakeReturnValue {
+        destination_register: usize,
+    },
     Add {
         left: u8,
         right: u8,
@@ -104,6 +110,9 @@ pub enum Instruction {
         offset: isize,
     },
     Return,
+    DumpState {
+        message: String
+    }
 }
 
 #[derive(Debug, Clone)]
@@ -121,8 +130,11 @@ pub enum Immediate {
 #[derive(Debug, Clone)]
 pub enum Location {
     Register(usize),
-    Stack {
+    StackFrameBase {
-        offset: usize,
+        offset: isize,
+    },
+    StackTop {
+        offset: isize,
     },
     Field {
         object_register: usize,
@@ -131,6 +143,6 @@ pub enum Location {
     Array {
         array_register: usize,
         index_register: usize,
-        offset: Option<isize>,
+        offset: isize,
     },
 }

src/vm/mod.rs

@@ -43,10 +43,12 @@ pub fn dump_state(state: &DvmState, message: &str) {
     for (i, register) in state.registers.iter().enumerate() {
         println!("\tr{:x}: {:?}", i, register);
     }
+    println!("Return value register: {}", state.return_value_register);
     println!("Call stack:");
     for call in state.call_stack.iter() {
         println!("\t{}", call);
     }
+    println!("Frame base index: {}", state.frame_base_index);
     println!("Stack:");
     for (i, value) in state.stack.iter().enumerate() {
         println!("\t{}: {}", i, value);
@@ -63,10 +65,13 @@ macro_rules! dvm_panic {
 
 pub type PlatformFunction = fn(state: &mut DvmState, context: &DvmContext);
 
+#[derive(Clone)]
 pub struct DvmState {
     call_stack: Vec<DvmCall>,
     current_instruction: Option<Instruction>,
+    frame_base_index: usize,
     registers: Vec<DvmValue>,
+    return_value_register: DvmValue,
     stack: Vec<DvmValue>,
 }
 
@@ -75,7 +80,9 @@ impl DvmState {
         DvmState {
             call_stack: vec![],
             current_instruction: None,
+            frame_base_index: 0,
             registers: vec![DvmValue::Empty; 16],
+            return_value_register: DvmValue::Empty,
             stack: vec![],
         }
     }
@@ -87,8 +94,14 @@ impl DvmState {
     }
 
     pub fn get_stack_argument(&self, index: usize) -> DvmValue {
+        let target_index = self
+            .frame_base_index
+            .checked_sub(1 + index)
+            .unwrap_or_else(|| {
+                dvm_panic!(self, "Unsigned overflow: calculated negative target_index.");
+            });
         self.stack
-            .get(self.stack.len() - 2 - index)
+            .get(target_index)
             .unwrap_or_else(|| {
                 dvm_panic!(self, "Stack underflow!");
             })
@@ -150,6 +163,7 @@ impl DvmContext {
     }
 }
 
+#[derive(Clone)]
 pub struct DvmCall {
     function_name: Rc<String>,
     source_code_location: SourceCodeLocation,
@@ -169,9 +183,9 @@ impl Display for DvmCall {
 
 fn update_index(index: &mut usize, offset: isize) {
     if offset.is_negative() {
-        *index -= offset.abs() as usize;
+        *index -= offset.unsigned_abs();
     } else {
-        *index += offset as usize;
+        *index += offset.unsigned_abs();
     }
 }
 
@@ -193,27 +207,40 @@ fn pop_call_frame(state: &mut DvmState) {
 fn compute_index_with_offset(
     registers: &Vec<DvmValue>,
     index_register: usize,
-    offset: &Option<isize>,
+    offset: isize,
 ) -> usize {
     let index = registers[index_register].as_usize().expect(&format!(
         "Could not convert the value of index_register {} to usize; found {:?}",
         index_register, registers[index_register]
     ));
-    if let Some(o) = offset {
+    if offset.is_negative() {
-        if o.is_negative() {
+        index - offset.unsigned_abs()
-            index - o.unsigned_abs()
     } else {
-            index + o.unsigned_abs()
+        index + offset.unsigned_abs()
-        }
-    } else {
-        index
     }
 }
 
 fn copy_from_source(state: &DvmState, source: &Location) -> DvmValue {
     match source {
         Location::Register(register) => state.registers[*register].clone(),
-        Location::Stack { offset } => state.stack[*offset].clone(),
+        Location::StackFrameBase { offset } => {
+            let index = if offset.is_negative() {
+                state.frame_base_index - offset.unsigned_abs()
+            } else {
+                state.frame_base_index + offset.unsigned_abs()
+            };
+            state.stack[index].clone()
+        }
+        Location::StackTop { offset } => {
+            if *offset >= 0 {
+                dvm_panic!(
+                    state,
+                    &format!("Offset {} out of bounds (must be negative)", offset)
+                );
+            }
+            let stack_length = state.stack.len();
+            state.stack[stack_length - offset.unsigned_abs()].clone()
+        }
         Location::Field {
             object_register,
             field_name,
@@ -228,7 +255,7 @@ fn copy_from_source(state: &DvmState, source: &Location) -> DvmValue {
             index_register,
             offset,
         } => {
-            let index = compute_index_with_offset(&state.registers, *index_register, offset);
+            let index = compute_index_with_offset(&state.registers, *index_register, *offset);
             state.registers[*array_register].map_array(
                 |a| a.borrow().read_element(index),
                 |v| {
@@ -244,8 +271,26 @@ fn write_to_destination(state: &mut DvmState, destination: &Location, value: Dvm
         Location::Register(register) => {
             state.registers[*register] = value;
         }
-        Location::Stack { offset } => {
+        Location::StackFrameBase { offset } => {
-            state.stack[*offset] = value;
+            let index = if offset.is_negative() {
+                state.frame_base_index - offset.unsigned_abs()
+            } else {
+                state.frame_base_index + offset.unsigned_abs()
+            };
+            state.stack[index] = value;
+        }
+        Location::StackTop { offset } => {
+            if *offset >= 0 {
+                dvm_panic!(
+                    state,
+                    &format!(
+                        "Stack top offset {} is out of range (must be negative)",
+                        offset
+                    )
+                );
+            }
+            let stack_length = state.stack.len();
+            state.stack[stack_length - offset.unsigned_abs()] = value;
         }
         Location::Field {
             object_register,
@@ -261,7 +306,7 @@ fn write_to_destination(state: &mut DvmState, destination: &Location, value: Dvm
             index_register,
             offset,
         } => {
-            let index = compute_index_with_offset(&state.registers, *index_register, offset);
+            let index = compute_index_with_offset(&state.registers, *index_register, *offset);
             state.registers[*array_register]
                 .expect_array()
                 .borrow_mut()
@@ -310,7 +355,9 @@ fn immediate_to_value(immediate: &Immediate) -> DvmValue {
 }
 
 pub fn run_main_function(state: &mut DvmState, context: &DvmContext) -> i32 {
-    let main_function = context.static_functions.get(&context.main_function)
+    let main_function = context
+        .static_functions
+        .get(&context.main_function)
         .expect(&format!("No such main function: {}", context.main_function));
     push_call_frame(
         Rc::new(main_function.fqn().to_string()),
@@ -319,23 +366,29 @@ pub fn run_main_function(state: &mut DvmState, context: &DvmContext) -> i32 {
     );
     run(main_function.instructions(), state, context);
     pop_call_frame(state);
-    state.pop_stack().expect_int_or_else(|v| {
+    state.return_value_register.expect_int_or_else(|v| {
-        dvm_panic!(state, &format!("Expected DvmValue::Int, but found {}", v));
+        dvm_panic!(
+            state,
+            &format!("Expected main to return DvmValue::Int, but found {}", v)
+        );
     })
 }
 
 // TODO: find all possible unwraps/expects and wrap with call to dvm_panic
 pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmContext) {
+    state.frame_base_index = state.stack.len();
     let mut index = 0;
     while index < instructions.len() {
-        state.current_instruction = Some(instructions[index].clone());
+        let current_instruction = &instructions[index];
+        state.current_instruction = Some(current_instruction.clone());
+        index += 1;
         use Instruction::*;
-        match &instructions[index] {
+        match current_instruction {
             MoveImmediate {
-                destination,
+                destination_register,
                 immediate,
             } => {
-                write_to_destination(state, destination, immediate_to_value(immediate));
+                state.registers[*destination_register] = immediate_to_value(immediate);
             }
             Copy {
                 source,
@@ -392,9 +445,18 @@ pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmCont
                     .clone();
 
                 // Do call
-                state.stack.push(DvmValue::Empty); // space for return value
+                // before:
+                // - push call frame
+                // - save current frame base index
+                // - set current frame base index to current stack size
                 push_call_frame(function_name.clone(), source_code_location.clone(), state);
+                let saved_frame_base_index = state.frame_base_index;
+                state.frame_base_index = state.stack.len();
+                // actual call
                 run(static_function.instructions(), state, context);
+
+                // reverse order
+                state.frame_base_index = saved_frame_base_index;
                 pop_call_frame(state);
             }
             InvokeObject {
@@ -426,12 +488,12 @@ pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmCont
                 let instructions = function.instructions();
 
                 // Do call
-                state.stack.push(DvmValue::Empty); // space for return value
-                state.stack.push(object_value); // self object
                 push_call_frame(function_name.clone(), source_code_location.clone(), state);
+                let saved_frame_base_index = state.frame_base_index;
+                state.frame_base_index = state.stack.len();
                 run(instructions, state, context);
+                state.frame_base_index = saved_frame_base_index;
                 pop_call_frame(state);
-                state.stack.pop(); // self object
             }
             InvokeStaticPlatform {
                 function_name,
@@ -449,9 +511,11 @@ pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmCont
                     });
 
                 // Do call
-                state.stack.push(DvmValue::Empty); // space for return value
                 push_call_frame(function_name.clone(), source_code_location.clone(), state);
+                let saved_frame_base_index = state.frame_base_index;
+                state.frame_base_index = state.stack.len();
                 platform_function(state, context);
+                state.frame_base_index = saved_frame_base_index;
                 pop_call_frame(state);
             }
             InvokeObjectPlatform {
@@ -483,12 +547,22 @@ pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmCont
                 }
 
                 // Do call
-                state.stack.push(DvmValue::Empty); // space for return value
-                state.stack.push(object_value); // self object
                 push_call_frame(function_name.clone(), source_code_location.clone(), state);
+                let saved_frame_base_index = state.frame_base_index;
+                state.frame_base_index = state.stack.len();
                 object_platform_function(state, context);
+                state.frame_base_index = saved_frame_base_index;
                 pop_call_frame(state);
-                state.stack.pop(); // self object
+            }
+            SetReturnValue { source_register } => {
+                state.return_value_register =
+                    std::mem::take(&mut state.registers[*source_register]);
+            }
+            TakeReturnValue {
+                destination_register,
+            } => {
+                state.registers[*destination_register] =
+                    std::mem::take(&mut state.return_value_register);
             }
             Add { .. } => {}
             Subtract { .. } => {}
@@ -518,7 +592,7 @@ pub fn run(instructions: &[Instruction], state: &mut DvmState, context: &DvmCont
             Return => {
                 break;
             }
-        }
+            DumpState { message } => dump_state(state, message),
-        index += 1;
+        }
     }
 }