Implemented basic support for function pointers

src/asm/Finalize.go

@@ -26,6 +26,7 @@ func (a Assembler) Finalize(dlls dll.List) ([]byte, []byte) {
 		dataLabels   map[string]Address
 		codePointers []*Pointer
 		dataPointers []*Pointer
+		funcPointers []*Pointer
 		dllPointers  []*Pointer
 	)
 
@@ -293,6 +294,33 @@ func (a Assembler) Finalize(dlls dll.List) ([]byte, []byte) {
 				} else {
 					code = x64.StoreDynamicNumber(code, operands.Address.Base, operands.Address.OffsetRegister, operands.Address.Length, operands.Number)
 				}
+			case *MemoryLabel:
+				start := len(code)
+
+				if operands.Address.OffsetRegister == math.MaxUint8 {
+					code = x64.StoreNumber(code, operands.Address.Base, operands.Address.Offset, operands.Address.Length, 0b00_00_00_00)
+				} else {
+					code = x64.StoreDynamicNumber(code, operands.Address.Base, operands.Address.OffsetRegister, operands.Address.Length, 0b00_00_00_00)
+				}
+
+				size := 4
+				opSize := len(code) - size - start
+				memLabel := x.Data.(*MemoryLabel)
+
+				funcPointers = append(funcPointers, &Pointer{
+					Position: Address(len(code) - size),
+					OpSize:   uint8(opSize),
+					Size:     uint8(size),
+					Resolve: func() Address {
+						destination, exists := codeLabels[memLabel.Label]
+
+						if !exists {
+							panic("unknown label")
+						}
+
+						return Address(destination)
+					},
+				})
 			case *MemoryRegister:
 				if operands.Address.OffsetRegister == math.MaxUint8 {
 					code = x64.StoreRegister(code, operands.Address.Base, operands.Address.Offset, operands.Address.Length, operands.Register)
@@ -397,6 +425,12 @@ restart:
 	dataStart, _ := fs.Align(codeStart+Address(len(code)), config.Align)
 	data, dataLabels = a.Data.Finalize()
 
+	for _, pointer := range funcPointers {
+		address := config.BaseAddress + Address(codeStart) + pointer.Resolve()
+		slice := code[pointer.Position : pointer.Position+4]
+		binary.LittleEndian.PutUint32(slice, uint32(address))
+	}
+
 	for _, pointer := range dataPointers {
 		address := config.BaseAddress + Address(dataStart) + pointer.Resolve()
 		slice := code[pointer.Position : pointer.Position+4]

src/asm/MemoryLabel.go

@@ -0,0 +1,27 @@
+package asm
+
+import (
+	"fmt"
+)
+
+// MemoryLabel operates with a memory address and a number.
+type MemoryLabel struct {
+	Address Memory
+	Label   string
+}
+
+// String returns a human readable version.
+func (data *MemoryLabel) String() string {
+	return fmt.Sprintf("%dB [%s+%s+%d], %s", data.Address.Length, data.Address.Base, data.Address.OffsetRegister, data.Address.Offset, data.Label)
+}
+
+// MemoryLabel adds an instruction with a memory address and a label.
+func (a *Assembler) MemoryLabel(mnemonic Mnemonic, address Memory, label string) {
+	a.Instructions = append(a.Instructions, Instruction{
+		Mnemonic: mnemonic,
+		Data: &MemoryLabel{
+			Address: address,
+			Label:   label,
+		},
+	})
+}