Hotfix: runtime error when trying to shift a negative amount in RISC-V

gboncoffee · Jul 11, 2024 · 447e3eb · 447e3eb
1 parent 3cb5549
commit 447e3eb
Showing 1 changed file with 12 additions and 5 deletions.
diff --git a/riscv/riscv.go b/riscv/riscv.go
@@ -127,7 +127,7 @@ func parseJ(i uint32) (uint8, uint32) {
 	return rd, signExtend(imm, 20)
 }
 
-func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func7 uint8) {
+func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func7 uint8) error {
 	rs1v64, _ := m.GetRegister(uint64(rs1))
 	rs1v := int32(rs1v64)
 	rs2v64, _ := m.GetRegister(uint64(rs2))
@@ -146,7 +146,7 @@ func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func
 		case 0x2:
 			rs1v64 := int64(signExtend64(uint32(rs1v)))
 			rs2v64 := int64(uint64(rs2v)) & 0x00000000ffffffff
-			tmp := int64(rs1v64 * rs2v64) >> 32
+			tmp := int64(rs1v64*rs2v64) >> 32
 			r = int32(tmp)
 		case 0x3:
 			rs1v64 := uint64(rs1v) & 0x00000000ffffffff
@@ -187,7 +187,7 @@ func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func
 				r = rs1v + rs2v
 			}
 		case 0x1:
-			r = rs1v << rs2v
+			r = int32(uint32(rs1v) << uint32(rs2v))
 		case 0x2:
 			// In C this would look terrible but in Go bools and ints are different.
 			if rs1v < rs2v {
@@ -206,6 +206,9 @@ func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func
 			r = rs1v ^ rs2v
 		case 0x5:
 			if func7 == 0x20 {
+				if rs2v < 0 {
+					return fmt.Errorf("error executing sra: negative shift amount")
+				}
 				r = rs1v >> rs2v
 			} else {
 				r = int32(uint32(rs1v) >> uint32(rs2v))
@@ -220,6 +223,8 @@ func (m *RiscV) execArithmetic(rd uint8, rs1 uint8, rs2 uint8, func3 uint8, func
 	m.SetRegister(uint64(rd), uint64(r))
 
 	m.pc += 4
+
+	return nil
 }
 
 func (m *RiscV) execImmArithmetic(rd uint8, rs1 uint8, imm uint32, func3 uint8) {
@@ -395,10 +400,12 @@ func (m *RiscV) execAuipc(rd uint8, imm uint32) {
 
 func (m *RiscV) execute(i uint32) (*machine.Call, error) {
 	opcode := i & 0b01111111
+	var err error = nil
+
 	switch opcode {
 	case 0b0110011:
 		rd, rs1, rs2, func3, func7 := parseR(i)
-		m.execArithmetic(rd, rs1, rs2, func3, func7)
+		err = m.execArithmetic(rd, rs1, rs2, func3, func7)
 	case 0b0010011:
 		rd, rs1, imm, func3 := parseI(i)
 		m.execImmArithmetic(rd, rs1, imm, func3)
@@ -439,7 +446,7 @@ func (m *RiscV) execute(i uint32) (*machine.Call, error) {
 		return nil, fmt.Errorf(machine.InterCtx.Get("unknown opcode: %b"), opcode)
 	}
 
-	return nil, nil
+	return nil, err
 }
 
 func (m *RiscV) LoadProgram(program []uint8) error {