ft(interpreter): impl push/pop

src/interpreter/computer.rs

@@ -1,16 +1,23 @@
 use core::fmt;
 
-use crate::operands::{ImmediateOperand, ModRmTarget};
+use crate::operands::{ImmediateOperand, MemoryIndex, ModRmTarget};
 
-use super::{flags::Flags, memory::Memory, register::Register};
+use super::{flags::Flags, interpreter::InterpreterError, memory::Memory, register::Register};
 
-/// Wrapper for easier argument passing of multi-type operations.
+/// Wrapper for easier argument passing of polymorph arithmetic operations.
 #[derive(Debug, Clone)]
 pub enum Operand {
     Immediate(crate::operands::ImmediateOperand),
     ModRmTarget(ModRmTarget),
 }
 
+/// Wrapper for easier argument passing of polymorph pop operations.
+#[derive(Debug, Clone)]
+pub enum PopTarget {
+    Register(crate::register::Register),
+    MemoryIndex(MemoryIndex),
+}
+
 type ArithmeticResult = ImmediateOperand;
 type Lhs = ImmediateOperand;
 type Rhs = ImmediateOperand;
@@ -31,6 +38,28 @@ impl Computer {
         }
     }
 
+    /// Decrement stack pointer and write `val` onto the stack.
+    pub fn push_stack(&mut self, val: ImmediateOperand) -> Result<(), InterpreterError> {
+        self.regs.push()?;
+        self.memory.write_raw(self.regs.sp, val.into())
+    }
+
+    /// Retrieve value from stack and increment stack pointer.
+    pub fn pop_stack(&mut self, target: PopTarget) -> Result<(), InterpreterError> {
+        let word = self.memory.read_raw(self.regs.sp)?;
+
+        match target {
+            PopTarget::Register(reg) => self.regs.write(reg, word.into()),
+            PopTarget::MemoryIndex(mem_idx) => self
+                .memory
+                .write_raw(Memory::calc_memidx(&self.regs, mem_idx).into(), word.into())?,
+        }
+
+        self.regs.pop()?;
+
+        Ok(())
+    }
+
     /// Perform binary `dest` = `dest` + `src`. Sets flags.
     pub fn add(&mut self, dest: ModRmTarget, src: Operand) {
         let op: fn(Lhs, Rhs) -> ArithmeticResult = |lhs, rhs| lhs + rhs;

src/interpreter/interpreter.rs

@@ -3,8 +3,8 @@ use std::{fmt::Debug, process::exit};
 
 use crate::{
     instructions::{Instruction, Mnemonic},
-    interpreter::{interrupt::Mess1, memory::Memory},
+    interpreter::{computer::PopTarget, interrupt::Mess1, memory::Memory},
-    operands::{Byte, ImmediateOperand, ModRmTarget},
+    operands::{Byte, ImmediateOperand, ModRmTarget, Word},
 };
 
 use super::{
@@ -17,8 +17,10 @@ type InstructionPointer<'a> = std::slice::Iter<'a, Instruction>;
 #[derive(Debug, Clone)]
 pub enum InterpreterError {
     EndOfData,
-    InvalidSyscall(u8),
+    InvalidSyscall(Byte),
-    InstructionNotFound(usize),
+    InstructionNotFound(Word),
+    MemoryOutOfBound(Word),
+    InvalidRegisterState(crate::interpreter::register::Register),
 }
 
 impl fmt::Display for InterpreterError {
@@ -31,6 +33,15 @@ impl fmt::Display for InterpreterError {
             InterpreterError::InstructionNotFound(addr) => {
                 write!(f, "IP({addr}) points at invalid instruction")
             }
+            InterpreterError::MemoryOutOfBound(addr) => {
+                write!(
+                    f,
+                    "Attempted memory write out of physical bounds: ({addr:#04x})"
+                )
+            }
+            InterpreterError::InvalidRegisterState(reg) => {
+                write!(f, "Invalid Register State: {reg:?}")
+            }
         }
     }
 }
@@ -90,10 +101,18 @@ impl Interpreter {
                 /*
                  * PUSH
                  */
+                Mnemonic::PUSH_R(reg) => self.computer.push_stack(self.computer.regs.read(reg))?,
+                Mnemonic::PUSH_Mod(target) => {
+                    self.computer.push_stack(self.computer.read_modrm(target))?
+                }
+                Mnemonic::PUSH_S(_) => todo!(),
 
                 /*
                  * POP
                  */
+                Mnemonic::POP_R(reg) => self.computer.pop_stack(PopTarget::Register(reg))?,
+                Mnemonic::POP_M(idx) => self.computer.pop_stack(PopTarget::MemoryIndex(idx))?,
+                Mnemonic::POP_S(_) => todo!(),
 
                 /*
                  * OR

src/interpreter/memory.rs

@@ -1,16 +1,47 @@
 use crate::operands::{Byte, Displacement, ImmediateOperand, MemoryIndex, Word};
 
+use super::interpreter::InterpreterError;
+
 #[derive(Debug, Clone, Copy)]
 pub struct Memory {
-    memory: [Byte; 65536],
+    memory: [Byte; Word::MAX as usize],
 }
 
 impl Memory {
     pub fn new() -> Self {
-        Self { memory: [0; 65536] }
+        Self {
+            memory: [0; Word::MAX as usize],
+        }
     }
 
-    // Write an [`ImmediateOperand`] to a memory location indexed by a [`MemoryIndex`].
+    /// Safely writes a [`Word`] into an index of memory.
+    pub fn write_raw(&mut self, idx: Word, val: Word) -> Result<(), InterpreterError> {
+        if idx + 1 > Word::MAX {
+            return Err(InterpreterError::MemoryOutOfBound(idx));
+        } else {
+            let [low, high] = val.to_le_bytes();
+            self.memory[idx as usize] = low;
+            self.memory[(idx + 1) as usize] = high;
+            Ok(())
+        }
+    }
+
+    /// Safely reads a [`Word`] from an index of memory
+    pub fn read_raw(&self, idx: Word) -> Result<Word, InterpreterError> {
+        let b1 = self
+            .memory
+            .get(idx as usize)
+            .ok_or(InterpreterError::MemoryOutOfBound(idx))?
+            .to_owned();
+        let b2 = self
+            .memory
+            .get((idx + 1) as usize)
+            .ok_or(InterpreterError::MemoryOutOfBound(idx))?
+            .to_owned();
+        Ok(Word::from_be_bytes([b1, b2]))
+    }
+
+    /// Write an [`ImmediateOperand`] to a memory location indexed by a [`MemoryIndex`].
     pub fn write(
         &mut self,
         regs: &crate::interpreter::register::Register,

src/interpreter/register.rs

@@ -1,6 +1,8 @@
 use crate::operands::{Byte, ImmediateOperand, Word};
 use core::fmt;
 
+use super::interpreter::InterpreterError;
+
 #[derive(Debug, Clone, Copy)]
 pub struct Register {
     pub ax: AX,
@@ -20,13 +22,33 @@ impl Register {
             bx: BX::new(),
             cx: CX::new(),
             dx: DX::new(),
-            sp: 0,
+            sp: 0xffff,
             bp: 0,
             si: 0,
             di: 0,
         }
     }
 
+    /// Decrement stack pointer
+    pub fn push(&mut self) -> Result<(), InterpreterError> {
+        if self.sp <= 2 {
+            return Err(InterpreterError::InvalidRegisterState(*self));
+        } else {
+            self.sp -= 2;
+            Ok(())
+        }
+    }
+
+    /// Increment stack pointer
+    pub fn pop(&mut self) -> Result<(), InterpreterError> {
+        if self.sp >= 0xffff - 2 {
+            return Err(InterpreterError::InvalidRegisterState(*self));
+        } else {
+            self.sp += 2;
+            Ok(())
+        }
+    }
+
     /// Read value from a [`crate::register::Register`].
     pub fn read(&self, reg: crate::register::Register) -> ImmediateOperand {
         match reg {

src/operands.rs

@@ -34,9 +34,9 @@ impl ImmediateOperand {
         match self {
             Self::Byte(_) => {
                 return if self.msb() {
-                    self.flip_sign().as_word().flip_sign()
+                    self.flip_sign().word().flip_sign()
                 } else {
-                    self.as_word()
+                    self.word()
                 };
             }
             Self::Word(_) => self,
@@ -46,7 +46,7 @@ impl ImmediateOperand {
     /// Interprets [`Self::Byte`] as [`Self::Word`].
     /// Returns word, if already a [`Self::Word`].
     /// CAUTION: You probably want to use [`Self::sign_extend()`] instead.
-    fn as_word(self) -> Self {
+    fn word(self) -> Self {
         match self {
             Self::Byte(b) => Self::Word(b as Word),
             Self::Word(_) => self,
@@ -566,7 +566,7 @@ mod tests {
         let b: u8 = 5;
         let byte = ImmediateOperand::Byte(b);
         let word = ImmediateOperand::Word(b as Word);
-        assert_eq!(byte.as_word(), word);
+        assert_eq!(byte.word(), word);
         assert_eq!(word, word);
     }