Implemented function calls

src/build/asm/Assembler.go

@@ -4,7 +4,6 @@ import (
 	"encoding/binary"
 
 	"git.akyoto.dev/cli/q/src/build/arch/x64"
-	"git.akyoto.dev/cli/q/src/build/config"
 )
 
 // Assembler contains a list of instructions.
@@ -23,19 +22,14 @@ func New() *Assembler {
 func (a *Assembler) Finalize() ([]byte, []byte) {
 	code := make([]byte, 0, len(a.Instructions)*8)
 	data := make([]byte, 0, 16)
+	labels := map[string]Address{}
 	pointers := []Pointer{}
 
 	for _, x := range a.Instructions {
 		switch x.Mnemonic {
 		case MOVE:
-			code = x64.MoveRegNum32(code, uint8(x.Data.(*RegisterNumber).Register), uint32(x.Data.(*RegisterNumber).Number))
-
-			if x.Data.(*RegisterNumber).IsPointer {
-				pointers = append(pointers, Pointer{
-					Position: Address(len(code) - 4),
-					Address:  Address(x.Data.(*RegisterNumber).Number),
-				})
-			}
+			regNum := x.Data.(*RegisterNumber)
+			code = x64.MoveRegNum32(code, uint8(regNum.Register), uint32(regNum.Number))
 
 		case RETURN:
 			code = x64.Return(code)
@@ -43,17 +37,33 @@ func (a *Assembler) Finalize() ([]byte, []byte) {
 		case SYSCALL:
 			code = x64.Syscall(code)
 
+		case CALL:
+			code = x64.Call(code, 0x00_00_00_00)
+			label := x.Data.(*Label)
+			nextInstructionAddress := len(code)
+
+			pointers = append(pointers, Pointer{
+				Position: Address(len(code) - 4),
+				Resolve: func() Address {
+					destination := labels[label.Name]
+					distance := int32(destination) - int32(nextInstructionAddress)
+					return Address(distance)
+				},
+			})
+
+		case LABEL:
+			labels[x.Data.(*Label).Name] = Address(len(code))
+
 		default:
 			panic("Unknown mnemonic: " + x.Mnemonic.String())
 		}
 	}
 
-	dataStart := config.BaseAddress + config.CodeOffset + Address(len(code))
+	// dataStart := config.BaseAddress + config.CodeOffset + Address(len(code))
 
 	for _, pointer := range pointers {
 		slice := code[pointer.Position : pointer.Position+4]
-		address := dataStart + pointer.Address
-		binary.LittleEndian.PutUint32(slice, address)
+		binary.LittleEndian.PutUint32(slice, pointer.Resolve())
 	}
 
 	return code, data

src/build/asm/Instructions.go

@@ -7,21 +7,28 @@ func (a *Assembler) MoveRegisterNumber(reg cpu.Register, number uint64) {
 	a.Instructions = append(a.Instructions, Instruction{
 		Mnemonic: MOVE,
 		Data: &RegisterNumber{
-			Register:  reg,
-			Number:    number,
-			IsPointer: false,
+			Register: reg,
+			Number:   number,
 		},
 	})
 }
 
-// MoveRegisterAddress moves an address into the given register.
-func (a *Assembler) MoveRegisterAddress(reg cpu.Register, address Address) {
+// Label adds a label at the current position.
+func (a *Assembler) Label(name string) {
 	a.Instructions = append(a.Instructions, Instruction{
-		Mnemonic: MOVE,
-		Data: &RegisterNumber{
-			Register:  reg,
-			Number:    uint64(address),
-			IsPointer: true,
+		Mnemonic: LABEL,
+		Data: &Label{
+			Name: name,
+		},
+	})
+}
+
+// Call calls a function whose position is identified by a label.
+func (a *Assembler) Call(name string) {
+	a.Instructions = append(a.Instructions, Instruction{
+		Mnemonic: CALL,
+		Data: &Label{
+			Name: name,
 		},
 	})
 }

src/build/asm/Label.go

@@ -0,0 +1,11 @@
+package asm
+
+// Label represents a jump label.
+type Label struct {
+	Name string
+}
+
+// String returns a human readable version.
+func (data *Label) String() string {
+	return data.Name
+}

src/build/asm/Mnemonic.go

@@ -7,6 +7,8 @@ const (
 	MOVE
 	RETURN
 	SYSCALL
+	LABEL
+	CALL
 )
 
 // String returns a human readable version.
@@ -20,6 +22,12 @@ func (m Mnemonic) String() string {
 
 	case SYSCALL:
 		return "syscall"
+
+	case LABEL:
+		return "label"
+
+	case CALL:
+		return "call"
 	}
 
 	return "NONE"

src/build/asm/Pointer.go

@@ -5,8 +5,8 @@ type Address = uint32
 
 // Pointer stores a relative memory address that we can later turn into an absolute one.
 // Position: The machine code offset where the address was inserted.
-// Address:  The offset inside the section.
+// Resolve:  The function that will return the final address.
 type Pointer struct {
-	Position uint32
-	Address  uint32
+	Position Address
+	Resolve  func() Address
 }

src/build/asm/RegisterNumber.go

@@ -8,9 +8,8 @@ import (
 
 // RegisterNumber operates with a register and a number.
 type RegisterNumber struct {
-	Register  cpu.Register
-	Number    uint64
-	IsPointer bool
+	Register cpu.Register
+	Number   uint64
 }
 
 // String returns a human readable version.