cmd/asm: fix some fuzz bugs

One (12466) was an actual logic error, backing up when there was
nothing there. The others were due to continuing to process an
instruction when it cannot work.

Methodically stop assembling an instruction when it's not going to
succeed.

Fixes #12466.
Fixes #12467.
Fixes #12468.

Change-Id: I88c568f2b9c1a8408043b2ac5a78f5e2ffd62abd
Reviewed-on: https://go-review.googlesource.com/14498Reviewed-by: Andrew Gerrand <adg@golang.org>

src/cmd/asm/internal/asm/asm.go

@@ -27,15 +27,18 @@ func (p *Parser) append(prog *obj.Prog, cond string, doLabel bool) {
 		case '5':
 			if !arch.ARMConditionCodes(prog, cond) {
 				p.errorf("unrecognized condition code .%q", cond)
+				return
 			}
 
 		case '7':
 			if !arch.ARM64Suffix(prog, cond) {
 				p.errorf("unrecognized suffix .%q", cond)
+				return
 			}
 
 		default:
 			p.errorf("unrecognized suffix .%q", cond)
+			return
 		}
 	}
 	if p.firstProg == nil {
@@ -49,6 +52,7 @@ func (p *Parser) append(prog *obj.Prog, cond string, doLabel bool) {
 		for _, label := range p.pendingLabels {
 			if p.labels[label] != nil {
 				p.errorf("label %q multiply defined", label)
+				return
 			}
 			p.labels[label] = prog
 		}
@@ -67,8 +71,7 @@ func (p *Parser) append(prog *obj.Prog, cond string, doLabel bool) {
 func (p *Parser) validateSymbol(pseudo string, addr *obj.Addr, offsetOk bool) {
 	if addr.Name != obj.NAME_EXTERN && addr.Name != obj.NAME_STATIC || addr.Scale != 0 || addr.Reg != 0 {
 		p.errorf("%s symbol %q must be a symbol(SB)", pseudo, symbolName(addr))
-	}
-	if !offsetOk && addr.Offset != 0 {
+	} else if !offsetOk && addr.Offset != 0 {
 		p.errorf("%s symbol %q must not be offset from SB", pseudo, symbolName(addr))
 	}
 }
@@ -144,6 +147,7 @@ func (p *Parser) asmText(word string, operands [][]lex.Token) {
 		// There is an argument size. It must be a minus sign followed by a non-negative integer literal.
 		if len(op) != 2 || op[0].ScanToken != '-' || op[1].ScanToken != scanner.Int {
 			p.errorf("TEXT %s: argument size must be of form -integer", name)
+			return
 		}
 		argSize = p.positiveAtoi(op[1].String())
 	}
@@ -195,11 +199,13 @@ func (p *Parser) asmData(word string, operands [][]lex.Token) {
 		// OK
 	default:
 		p.errorf("DATA value must be an immediate constant or address")
+		return
 	}
 
 	// The addresses must not overlap. Easiest test: require monotonicity.
 	if lastAddr, ok := p.dataAddr[name]; ok && nameAddr.Offset < lastAddr {
 		p.errorf("overlapping DATA entry for %s", name)
+		return
 	}
 	p.dataAddr[name] = nameAddr.Offset + int64(scale)
 
@@ -340,6 +346,7 @@ func (p *Parser) asmJump(op int, cond string, a []obj.Addr) {
 			reg, ok := p.arch.RegisterNumber("R", int16(reg))
 			if !ok {
 				p.errorf("bad register number %d", reg)
+				return
 			}
 			prog.Reg = reg
 			break
@@ -390,6 +397,7 @@ func (p *Parser) asmJump(op int, cond string, a []obj.Addr) {
 		prog.To = a[0]
 	default:
 		p.errorf("cannot assemble jump %+v", target)
+		return
 	}
 
 	p.append(prog, cond, true)
@@ -400,9 +408,9 @@ func (p *Parser) patch() {
 		targetProg := p.labels[patch.label]
 		if targetProg == nil {
 			p.errorf("undefined label %s", patch.label)
-		} else {
-			p.branch(patch.prog, targetProg)
+			return
 		}
+		p.branch(patch.prog, targetProg)
 	}
 	p.toPatch = p.toPatch[:0]
 }
@@ -468,6 +476,7 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 					break
 				}
 				p.errorf("unrecognized addressing for %s", obj.Aconv(op))
+				return
 			}
 			if arch.IsARMFloatCmp(op) {
 				prog.From = a[0]
@@ -506,6 +515,7 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 				prog.To = a[1]
 				if a[2].Type != obj.TYPE_REG {
 					p.errorf("invalid addressing modes for third operand to %s instruction, must be register", obj.Aconv(op))
+					return
 				}
 				prog.RegTo2 = a[2].Reg
 				break
@@ -541,9 +551,11 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 				prog.To = a[2]
 			default:
 				p.errorf("invalid addressing modes for %s instruction", obj.Aconv(op))
+				return
 			}
 		default:
 			p.errorf("TODO: implement three-operand instructions for this architecture")
+			return
 		}
 	case 4:
 		if p.arch.Thechar == '5' && arch.IsARMMULA(op) {
@@ -577,6 +589,7 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 			break
 		}
 		p.errorf("can't handle %s instruction with 4 operands", obj.Aconv(op))
+		return
 	case 5:
 		if p.arch.Thechar == '9' && arch.IsPPC64RLD(op) {
 			// Always reg, reg, con, con, reg.  (con, con is a 'mask').
@@ -598,6 +611,7 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 			break
 		}
 		p.errorf("can't handle %s instruction with 5 operands", obj.Aconv(op))
+		return
 	case 6:
 		if p.arch.Thechar == '5' && arch.IsARMMRC(op) {
 			// Strange special case: MCR, MRC.
@@ -621,6 +635,7 @@ func (p *Parser) asmInstruction(op int, cond string, a []obj.Addr) {
 		fallthrough
 	default:
 		p.errorf("can't handle %s instruction with %d operands", obj.Aconv(op), len(a))
+		return
 	}
 
 	p.append(prog, cond, true)

src/cmd/asm/internal/asm/operand_test.go

@@ -293,6 +293,7 @@ var armOperandTests = []operandTest{
 	{"[R0,R1,g,R15", ""}, // Issue 11764 - asm hung parsing ']' missing register lists.
 	{"[):[o-FP", ""},     // Issue 12469 - there was no infinite loop for ARM; these are just sanity checks.
 	{"[):[R0-FP", ""},
+	{"(", ""}, // Issue 12466 - backed up before beginning of line.
 }
 
 var ppc64OperandTests = []operandTest{

src/cmd/asm/internal/asm/parse.go

@@ -155,6 +155,7 @@ func (p *Parser) line() bool {
 					// Remember this location so we can swap the operands below.
 					if colon >= 0 {
 						p.errorf("invalid ':' in operand")
+						return true
 					}
 					colon = len(operands)
 				}
@@ -338,8 +339,13 @@ func (p *Parser) operand(a *obj.Addr) bool {
 	case scanner.Int, scanner.Float, scanner.String, scanner.Char, '+', '-', '~':
 		haveConstant = true
 	case '(':
-		// Could be parenthesized expression or (R).
-		rname := p.next().String()
+		// Could be parenthesized expression or (R). Must be something, though.
+		tok := p.next()
+		if tok.ScanToken == scanner.EOF {
+			p.errorf("missing right parenthesis")
+			return false
+		}
+		rname := tok.String()
 		p.back()
 		haveConstant = !p.atStartOfRegister(rname)
 		if !haveConstant {
@@ -361,6 +367,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 		if p.have(scanner.String) {
 			if prefix != '$' {
 				p.errorf("string constant must be an immediate")
+				return false
 			}
 			str, err := strconv.Unquote(p.get(scanner.String).String())
 			if err != nil {
@@ -952,7 +959,11 @@ func (p *Parser) next() lex.Token {
 }
 
 func (p *Parser) back() {
-	p.inputPos--
+	if p.inputPos == 0 {
+		p.errorf("internal error: backing up before BOL")
+	} else {
+		p.inputPos--
+	}
 }
 
 func (p *Parser) peek() lex.ScanToken {

src/cmd/asm/internal/asm/pseudo_test.go

@@ -35,6 +35,8 @@ func TestErroneous(t *testing.T) {
 		{"TEXT", "%", "expect two or three operands for TEXT"},
 		{"TEXT", "1, 1", "TEXT symbol \"<erroneous symbol>\" must be a symbol(SB)"},
 		{"TEXT", "$\"foo\", 0, $1", "TEXT symbol \"<erroneous symbol>\" must be a symbol(SB)"},
+		{"TEXT", "$0É:0, 0, $1", "expected EOF, found É"},   // Issue #12467.
+		{"TEXT", "$:0:(SB, 0, $1", "expected '(', found 0"}, // Issue 12468.
 		{"FUNCDATA", "", "expect two operands for FUNCDATA"},
 		{"FUNCDATA", "(SB ", "expect two operands for FUNCDATA"},
 		{"DATA", "", "expect two operands for DATA"},