Implement string out of bounds checks

src/runtime/runtime.go

@@ -56,3 +56,12 @@ func _panic(message interface{}) {
 	printnl()
 	C.exit(1)
 }
+
+func boundsCheck(s string, outOfRange bool) {
+	if outOfRange {
+		// printstring() here is safe as this function is excluded from bounds
+		// checking.
+		printstring("panic: runtime error: index out of range\n")
+		C.exit(1)
+	}
+}

tgo.go

@@ -44,6 +44,7 @@ type Compiler struct {
 	interfaceType   llvm.Type
 	typeassertType  llvm.Type
 	panicFunc       llvm.Value
+	boundsCheckFunc llvm.Value
 	printstringFunc llvm.Value
 	printintFunc    llvm.Value
 	printbyteFunc   llvm.Value
@@ -101,6 +102,9 @@ func NewCompiler(pkgName, triple string) (*Compiler, error) {
 	panicType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.interfaceType}, false)
 	c.panicFunc = llvm.AddFunction(c.mod, "runtime._panic", panicType)
 
+	boundsCheckType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.stringType, llvm.Int1Type()}, false)
+	c.boundsCheckFunc = llvm.AddFunction(c.mod, "runtime.boundsCheck", boundsCheckType)
+
 	printstringType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.stringType}, false)
 	c.printstringFunc = llvm.AddFunction(c.mod, "runtime.printstring", printstringType)
 	printintType := llvm.FunctionType(llvm.VoidType(), []llvm.Type{c.intType}, false)
@@ -476,13 +480,12 @@ func (c *Compiler) parseInstr(frame *Frame, instr ssa.Instruction) error {
 	}
 }
 
-func (c *Compiler) parseBuiltin(frame *Frame, instr *ssa.CallCommon, call *ssa.Builtin) (llvm.Value, error) {
-	fmt.Printf("    builtin: %v\n", call)
-	name := call.Name()
+func (c *Compiler) parseBuiltin(frame *Frame, args []ssa.Value, callName string) (llvm.Value, error) {
+	fmt.Printf("    builtin: %v\n", callName)
 
-	switch name {
+	switch callName {
 	case "print", "println":
-		for i, arg := range instr.Args {
+		for i, arg := range args {
 			if i >= 1 {
 				c.builder.CreateCall(c.printspaceFunc, nil, "")
 			}
@@ -507,17 +510,16 @@ func (c *Compiler) parseBuiltin(frame *Frame, instr *ssa.CallCommon, call *ssa.B
 				return llvm.Value{}, errors.New("unknown arg type: " + fmt.Sprintf("%#v", typ))
 			}
 		}
-		if name == "println" {
+		if callName == "println" {
 			c.builder.CreateCall(c.printnlFunc, nil, "")
 		}
 		return llvm.Value{}, nil // print() or println() returns void
 	case "len":
-		arg := instr.Args[0]
-		value, err := c.parseExpr(frame, arg)
+		value, err := c.parseExpr(frame, args[0])
 		if err != nil {
 			return llvm.Value{}, err
 		}
-		switch typ := arg.Type().(type) {
+		switch typ := args[0].Type().(type) {
 		case *types.Basic:
 			switch typ.Kind() {
 			case types.String:
@@ -529,7 +531,7 @@ func (c *Compiler) parseBuiltin(frame *Frame, instr *ssa.CallCommon, call *ssa.B
 			return llvm.Value{}, errors.New("todo: len: unknown type")
 		}
 	default:
-		return llvm.Value{}, errors.New("todo: builtin: " + name)
+		return llvm.Value{}, errors.New("todo: builtin: " + callName)
 	}
 }
 
@@ -564,7 +566,7 @@ func (c *Compiler) parseCall(frame *Frame, instr *ssa.Call) (llvm.Value, error)
 
 	switch call := instr.Common().Value.(type) {
 	case *ssa.Builtin:
-		return c.parseBuiltin(frame, instr.Common(), call)
+		return c.parseBuiltin(frame, instr.Common().Args, call.Name())
 	case *ssa.Function:
 		return c.parseFunctionCall(frame, instr.Common(), call)
 	default:
@@ -682,7 +684,22 @@ func (c *Compiler) parseExpr(frame *Frame, expr ssa.Value) (llvm.Value, error) {
 		if err != nil {
 			return llvm.Value{}, nil
 		}
-		// TODO: out-of-bounds checking
+
+		// Bounds check
+		// TODO: inline, and avoid if possible
+		if frame.llvmFn.Name() != "runtime.boundsCheck" {
+			constZero := llvm.ConstInt(c.intType, 0, false)
+			isNegative := c.builder.CreateICmp(llvm.IntSLT, index, constZero, "") // index < 0
+			strlen, err := c.parseBuiltin(frame, []ssa.Value{expr.X}, "len")
+			if err != nil {
+				return llvm.Value{}, err // shouldn't happen
+			}
+			isTooBig := c.builder.CreateICmp(llvm.IntSGE, index, strlen, "") // index >= len(value)
+			isOverflow := c.builder.CreateOr(isNegative, isTooBig, "")
+			c.builder.CreateCall(c.boundsCheckFunc, []llvm.Value{value, isOverflow}, "")
+		}
+
+		// Lookup byte
 		buf := c.builder.CreateExtractValue(value, 1, "")
 		bufPtr := c.builder.CreateGEP(buf, []llvm.Value{index}, "")
 		return c.builder.CreateLoad(bufPtr, ""), nil