Improved Windows DLL calls

src/asm/Finalize.go

@@ -113,24 +113,6 @@ func (a Assembler) Finalize(dlls dll.List) ([]byte, []byte) {
 
 			codePointers = append(codePointers, pointer)
 
-		case CALL_AT:
-			code = x64.CallAtAddress(code, 0x00_00_00_00)
-			size := 4
-			label := x.Data.(*Label)
-
-			pointer := &Pointer{
-				Position: Address(len(code) - size),
-				OpSize:   2,
-				Size:     uint8(size),
-			}
-
-			pointer.Resolve = func() Address {
-				index := dlls.Index("kernel32.dll", label.Name)
-				return Address(index * 8)
-			}
-
-			dllPointers = append(dllPointers, pointer)
-
 		case COMMENT:
 			continue
 
@@ -142,6 +124,36 @@ func (a Assembler) Finalize(dlls dll.List) ([]byte, []byte) {
 				code = x64.CompareRegisterRegister(code, operands.Destination, operands.Source)
 			}
 
+		case DLLCALL:
+			size := 4
+
+			code = x64.SubRegisterNumber(code, x64.RSP, 32)
+			code = x64.CallAtAddress(code, 0x00_00_00_00)
+			position := len(code) - size
+			code = x64.AddRegisterNumber(code, x64.RSP, 32)
+
+			label := x.Data.(*Label)
+			pointer := &Pointer{
+				Position: Address(position),
+				OpSize:   2,
+				Size:     uint8(size),
+			}
+
+			pointer.Resolve = func() Address {
+				dot := strings.Index(label.Name, ".")
+				library := label.Name[:dot]
+				funcName := label.Name[dot+1:]
+				index := dlls.Index(library, funcName)
+
+				if index == -1 {
+					panic("unknown DLL function " + label.Name)
+				}
+
+				return Address(index * 8)
+			}
+
+			dllPointers = append(dllPointers, pointer)
+
 		case JE, JNE, JG, JGE, JL, JLE, JUMP:
 			switch x.Mnemonic {
 			case JE:

src/asm/Instructions.go

@@ -20,6 +20,16 @@ func (a *Assembler) Call(name string) {
 	})
 }
 
+// DLLCall calls a function in a DLL file.
+func (a *Assembler) DLLCall(name string) {
+	a.Instructions = append(a.Instructions, Instruction{
+		Mnemonic: DLLCALL,
+		Data: &Label{
+			Name: name,
+		},
+	})
+}
+
 // Return returns back to the caller.
 func (a *Assembler) Return() {
 	if len(a.Instructions) > 0 {

src/asm/Mnemonic.go

@@ -29,7 +29,7 @@ const (
 
 	// Control flow
 	CALL
-	CALL_AT
+	DLLCALL
 	JE
 	JNE
 	JG
@@ -55,8 +55,8 @@ func (m Mnemonic) String() string {
 		return "and"
 	case CALL:
 		return "call"
-	case CALL_AT:
-		return "call at"
+	case DLLCALL:
+		return "dllcall"
 	case COMMENT:
 		return "comment"
 	case COMPARE: