cmd/asm: fix EOF message on operand parsing errors.

If the parsing of an operand completes but the parser thinks there
is more to read, return an "expected end of operand" error message
instead of "expected EOF." This also removes extra "asm: " prefixes
in error strings since "asm: " is already set as the global log
prefix.

Fixes #14071

Change-Id: I7d621c1aea529a0eca3bcba032359bd25b3e1080
Reviewed-on: https://go-review.googlesource.com/19731Reviewed-by: Rob Pike <r@golang.org>

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

@@ -297,7 +297,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 			p.errorf("illegal use of register list")
 		}
 		p.registerList(a)
-		p.expect(scanner.EOF)
+		p.expectOperandEnd()
 		return true
 	}
 
@@ -331,7 +331,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 			}
 		}
 		// fmt.Printf("REG %s\n", obj.Dconv(&emptyProg, 0, a))
-		p.expect(scanner.EOF)
+		p.expectOperandEnd()
 		return true
 	}
 
@@ -363,7 +363,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 			a.Type = obj.TYPE_FCONST
 			a.Val = p.floatExpr()
 			// fmt.Printf("FCONST %s\n", obj.Dconv(&emptyProg, 0, a))
-			p.expect(scanner.EOF)
+			p.expectOperandEnd()
 			return true
 		}
 		if p.have(scanner.String) {
@@ -378,7 +378,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 			a.Type = obj.TYPE_SCONST
 			a.Val = str
 			// fmt.Printf("SCONST %s\n", obj.Dconv(&emptyProg, 0, a))
-			p.expect(scanner.EOF)
+			p.expectOperandEnd()
 			return true
 		}
 		a.Offset = int64(p.expr())
@@ -392,7 +392,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 				a.Type = obj.TYPE_MEM
 			}
 			// fmt.Printf("CONST %d %s\n", a.Offset, obj.Dconv(&emptyProg, 0, a))
-			p.expect(scanner.EOF)
+			p.expectOperandEnd()
 			return true
 		}
 		// fmt.Printf("offset %d \n", a.Offset)
@@ -402,7 +402,7 @@ func (p *Parser) operand(a *obj.Addr) bool {
 	p.registerIndirect(a, prefix)
 	// fmt.Printf("DONE %s\n", p.arch.Dconv(&emptyProg, 0, a))
 
-	p.expect(scanner.EOF)
+	p.expectOperandEnd()
 	return true
 }
 
@@ -983,14 +983,19 @@ func (p *Parser) more() bool {
 
 // get verifies that the next item has the expected type and returns it.
 func (p *Parser) get(expected lex.ScanToken) lex.Token {
-	p.expect(expected)
+	p.expect(expected, expected.String())
 	return p.next()
 }
 
+// expectOperandEnd verifies that the parsing state is properly at the end of an operand.
+func (p *Parser) expectOperandEnd() {
+	p.expect(scanner.EOF, "end of operand")
+}
+
 // expect verifies that the next item has the expected type. It does not consume it.
-func (p *Parser) expect(expected lex.ScanToken) {
-	if p.peek() != expected {
-		p.errorf("expected %s, found %s", expected, p.next())
+func (p *Parser) expect(expectedToken lex.ScanToken, expectedMessage string) {
+	if p.peek() != expectedToken {
+		p.errorf("expected %s, found %s", expectedMessage, p.next())
 	}
 }
 

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

@@ -35,8 +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.
+		{"TEXT", "$0É:0, 0, $1", "expected end of operand, found É"}, // Issue #12467.
+		{"TEXT", "$: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"},

src/cmd/asm/internal/lex/input.go

@@ -30,7 +30,7 @@ type Input struct {
 	peekText        string
 }
 
-// NewInput returns a
+// NewInput returns an Input from the given path.
 func NewInput(name string) *Input {
 	return &Input{
 		// include directories: look in source dir, then -I directories.

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

@@ -77,7 +77,7 @@ func NewLexer(name string, ctxt *obj.Link) TokenReader {
 	input := NewInput(name)
 	fd, err := os.Open(name)
 	if err != nil {
-		log.Fatalf("asm: %s\n", err)
+		log.Fatalf("%s\n", err)
 	}
 	input.Push(NewTokenizer(name, fd, fd))
 	return input

src/cmd/asm/main.go

@@ -26,7 +26,7 @@ func main() {
 
 	architecture := arch.Set(GOARCH)
 	if architecture == nil {
-		log.Fatalf("asm: unrecognized architecture %s", GOARCH)
+		log.Fatalf("unrecognized architecture %s", GOARCH)
 	}
 
 	flags.Parse()
@@ -66,7 +66,7 @@ func main() {
 		obj.Writeobjdirect(ctxt, output)
 	}
 	if !ok || diag {
-		log.Printf("asm: assembly of %s failed", flag.Arg(0))
+		log.Printf("assembly of %s failed", flag.Arg(0))
 		os.Remove(*flags.OutputFile)
 		os.Exit(1)
 	}