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cmd/asm: fix several panics with erroneous input
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The parser tries to read as much information as possible,
issuing some errors when needed. Errors generally do not
stop the parsing.

With some pathological input, it may result in various
panics when the error message itself is built, or when the
next operand is parsed. It happens while parsing
pseudo-instructions.

For instance, the following lines all generate a panic:

	TEXT
	TEXT%
	TEXT 1,1
	TEXT $"toto", 0, $1
	FUNCDATA
	DATA 0
	DATA(0),1
	FUNCDATA(SB
	GLOBL 0, 1
	PCDATA 1

Added corresponding tests.

Introduced a writer in the parser to capture error messages
for testing purpose. It defaults to os.Stderr.

Added an explicit check when symbol names cannot be displayed.

Interrupted parsing early when the number of operands is wrong for
pseudo-instructions.

Note that the last point is a change of behavior, because some
operands will not get parsed anymore in case of early error.

IMO, it is acceptable, because only the first error of the line
is considered anyway. If it is not acceptable, it can probably
be improved at the price of a more verbose CL.

Fixes #11765
Fixes #11760
Fixes #11759

Change-Id: I9602a848132e358a1bccad794d7555e0823970dd
Reviewed-on: https://go-review.googlesource.com/13925
Reviewed-by: Rob Pike <[email protected]>
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dspezia authored and robpike committed Sep 2, 2015
1 parent dc3540d commit df37c4b
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Showing 3 changed files with 103 additions and 13 deletions.
22 changes: 18 additions & 4 deletions src/cmd/asm/internal/asm/asm.go
Original file line number Diff line number Diff line change
Expand Up @@ -66,10 +66,10 @@ func (p *Parser) append(prog *obj.Prog, cond string, doLabel bool) {
// validateSymbol checks that addr represents a valid name for a pseudo-op.
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, addr.Sym.Name)
p.errorf("%s symbol %q must be a symbol(SB)", pseudo, symbolName(addr))
}
if !offsetOk && addr.Offset != 0 {
p.errorf("%s symbol %q must not be offset from SB", pseudo, addr.Sym.Name)
p.errorf("%s symbol %q must not be offset from SB", pseudo, symbolName(addr))
}
}

Expand All @@ -91,6 +91,7 @@ func (p *Parser) validateImmediate(pseudo string, addr *obj.Addr) {
func (p *Parser) asmText(word string, operands [][]lex.Token) {
if len(operands) != 2 && len(operands) != 3 {
p.errorf("expect two or three operands for TEXT")
return
}

// Labels are function scoped. Patch existing labels and
Expand All @@ -102,7 +103,7 @@ func (p *Parser) asmText(word string, operands [][]lex.Token) {
// That means symbol plus indirect on SB and no offset.
nameAddr := p.address(operands[0])
p.validateSymbol("TEXT", &nameAddr, false)
name := nameAddr.Sym.Name
name := symbolName(&nameAddr)
next := 1

// Next operand is the optional text flag, a literal integer.
Expand Down Expand Up @@ -171,19 +172,21 @@ func (p *Parser) asmText(word string, operands [][]lex.Token) {
func (p *Parser) asmData(word string, operands [][]lex.Token) {
if len(operands) != 2 {
p.errorf("expect two operands for DATA")
return
}

// Operand 0 has the general form foo<>+0x04(SB)/4.
op := operands[0]
n := len(op)
if n < 3 || op[n-2].ScanToken != '/' || op[n-1].ScanToken != scanner.Int {
p.errorf("expect /size for DATA argument")
return
}
scale := p.parseScale(op[n-1].String())
op = op[:n-2]
nameAddr := p.address(op)
p.validateSymbol("DATA", &nameAddr, true)
name := nameAddr.Sym.Name
name := symbolName(&nameAddr)

// Operand 1 is an immediate constant or address.
valueAddr := p.address(operands[1])
Expand Down Expand Up @@ -220,6 +223,7 @@ func (p *Parser) asmData(word string, operands [][]lex.Token) {
func (p *Parser) asmGlobl(word string, operands [][]lex.Token) {
if len(operands) != 2 && len(operands) != 3 {
p.errorf("expect two or three operands for GLOBL")
return
}

// Operand 0 has the general form foo<>+0x04(SB).
Expand Down Expand Up @@ -257,6 +261,7 @@ func (p *Parser) asmGlobl(word string, operands [][]lex.Token) {
func (p *Parser) asmPCData(word string, operands [][]lex.Token) {
if len(operands) != 2 {
p.errorf("expect two operands for PCDATA")
return
}

// Operand 0 must be an immediate constant.
Expand All @@ -283,6 +288,7 @@ func (p *Parser) asmPCData(word string, operands [][]lex.Token) {
func (p *Parser) asmFuncData(word string, operands [][]lex.Token) {
if len(operands) != 2 {
p.errorf("expect two operands for FUNCDATA")
return
}

// Operand 0 must be an immediate constant.
Expand Down Expand Up @@ -622,6 +628,14 @@ func newAddr(x obj.Addr) *obj.Addr {
return p
}

// symbolName returns the symbol name, or an error string if none if available.
func symbolName(addr *obj.Addr) string {
if addr.Sym != nil {
return addr.Sym.Name
}
return "<erroneous symbol>"
}

var emptyProg obj.Prog

// getConstantPseudo checks that addr represents a plain constant and returns its value.
Expand Down
23 changes: 14 additions & 9 deletions src/cmd/asm/internal/asm/parse.go
Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@ package asm

import (
"fmt"
"io"
"log"
"os"
"strconv"
Expand Down Expand Up @@ -37,6 +38,7 @@ type Parser struct {
firstProg *obj.Prog
lastProg *obj.Prog
dataAddr map[string]int64 // Most recent address for DATA for this symbol.
errorWriter io.Writer
}

type Patch struct {
Expand All @@ -46,11 +48,12 @@ type Patch struct {

func NewParser(ctxt *obj.Link, ar *arch.Arch, lexer lex.TokenReader) *Parser {
return &Parser{
ctxt: ctxt,
arch: ar,
lex: lexer,
labels: make(map[string]*obj.Prog),
dataAddr: make(map[string]int64),
ctxt: ctxt,
arch: ar,
lex: lexer,
labels: make(map[string]*obj.Prog),
dataAddr: make(map[string]int64),
errorWriter: os.Stderr,
}
}

Expand All @@ -67,10 +70,12 @@ func (p *Parser) errorf(format string, args ...interface{}) {
return
}
p.errorLine = p.histLineNum
// Put file and line information on head of message.
format = "%s:%d: " + format + "\n"
args = append([]interface{}{p.lex.File(), p.lineNum}, args...)
fmt.Fprintf(os.Stderr, format, args...)
if p.lex != nil {
// Put file and line information on head of message.
format = "%s:%d: " + format + "\n"
args = append([]interface{}{p.lex.File(), p.lineNum}, args...)
}
fmt.Fprintf(p.errorWriter, format, args...)
p.errorCount++
if p.errorCount > 10 {
log.Fatal("too many errors")
Expand Down
71 changes: 71 additions & 0 deletions src/cmd/asm/internal/asm/pseudo_test.go
Original file line number Diff line number Diff line change
@@ -0,0 +1,71 @@
// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package asm

import (
"bytes"
"strings"
"testing"

"cmd/asm/internal/arch"
"cmd/asm/internal/lex"
)

func tokenize(s string) [][]lex.Token {
res := [][]lex.Token{}
if len(s) == 0 {
return res
}
for _, o := range strings.Split(s, ",") {
res = append(res, lex.Tokenize(o))
}
return res
}

func TestErroneous(t *testing.T) {

tests := []struct {
pseudo string
operands string
expected string
}{
{"TEXT", "", "expect two or three operands for TEXT"},
{"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)"},
{"FUNCDATA", "", "expect two operands for FUNCDATA"},
{"FUNCDATA", "(SB ", "expect two operands for FUNCDATA"},
{"DATA", "", "expect two operands for DATA"},
{"DATA", "0", "expect two operands for DATA"},
{"DATA", "(0), 1", "expect /size for DATA argument"},
{"GLOBL", "", "expect two or three operands for GLOBL"},
{"GLOBL", "0,1", "GLOBL symbol \"<erroneous symbol>\" must be a symbol(SB)"},
{"PCDATA", "", "expect two operands for PCDATA"},
{"PCDATA", "1", "expect two operands for PCDATA"},
}

// Note these errors should be independent of the architecture.
// Just run the test with amd64.
parser := newParser("amd64")
var buf bytes.Buffer
parser.errorWriter = &buf

for _, test := range tests {
parser.errorCount = 0
parser.lineNum++
parser.histLineNum++
op, ok := arch.Pseudos[test.pseudo]
if !ok {
t.Fatalf("Wrong pseudo-instruction: %s", test.pseudo)
}
parser.pseudo(op, test.pseudo, tokenize(test.operands))
errorLine := buf.String()
if test.expected != errorLine {
t.Errorf("Unexpected error %q; expected %q", errorLine, test.expected)
}
buf.Reset()
}

}

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