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working on disasm
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Zellyn Hunter
parent
a9f4d9b8ff
commit
d504143800
118
asm/disasm.go
118
asm/disasm.go
@ -4,58 +4,92 @@ Package asm provides routines for decompiling 6502 assembly language.
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package asm
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import (
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"bufio"
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"fmt"
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"io"
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"os"
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"regexp"
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"strconv"
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"github.com/zellyn/go6502/opcodes"
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)
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// Symbols are symbol tables used to convert addresses to names
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type Symbols map[int]string
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// name returns a symbol for an address. If lookback is 1 or greater,
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// it can return strings like "FOO+1" for the addresses succeeding
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// defined symbols.
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func (s Symbols) name(addr int, lookback int) string {
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if n, ok := s[addr]; ok {
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return n
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}
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for i := 1; i <= lookback; i++ {
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if n, ok := s[addr-i]; ok {
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return fmt.Sprintf("%s+%d", n, i)
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}
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}
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return ""
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}
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// bytesString takes three bytes and a length, returning the formatted
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// hex bytes for an instrction of the given length.
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func bytesString(byte0, byte1, byte2 byte, length int) string {
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switch length {
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case 1:
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return fmt.Sprintf("%02X ", byte0)
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return fmt.Sprintf("%02X", byte0)
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case 2:
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return fmt.Sprintf("%02X %02X ", byte0, byte1)
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return fmt.Sprintf("%02X %02X", byte0, byte1)
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case 3:
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return fmt.Sprintf("%02X %02X %02X", byte0, byte1, byte2)
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}
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panic("Length must be 1, 2, or 3")
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}
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func (s *Symbols) addr4(addr uint16, lookback int) string {
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if n := s.name(int(addr), lookback); n != "" {
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return n
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}
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return fmt.Sprintf("$%04X", addr)
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}
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func (s *Symbols) addr2(addr byte, lookback int) string {
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if n := s.name(int(addr), lookback); n != "" {
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return n
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}
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return fmt.Sprintf("$%02X", addr)
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}
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// addrString returns the address part of a 6502 assembly language
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// instruction.
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func addrString(pc uint16, byte1, byte2 byte, length int, mode opcodes.AddressingMode) string {
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func addrString(pc uint16, byte1, byte2 byte, length int, mode opcodes.AddressingMode, s Symbols, lookback int) string {
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addr16 := uint16(byte1) + uint16(byte2)<<8
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addrRel := uint16(int32(pc+2) + int32(int8(byte1)))
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switch mode {
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case opcodes.MODE_IMPLIED:
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return " "
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case opcodes.MODE_IMPLIED, opcodes.MODE_A:
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return ""
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case opcodes.MODE_ABSOLUTE:
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return fmt.Sprintf("$%04X ", addr16)
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return fmt.Sprintf("%s", s.addr4(addr16, lookback))
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case opcodes.MODE_INDIRECT:
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return fmt.Sprintf("($%04X)", addr16)
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return fmt.Sprintf("(%s)", s.addr4(addr16, lookback))
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case opcodes.MODE_RELATIVE:
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return fmt.Sprintf("$%04X ", addrRel)
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return fmt.Sprintf("%s", s.addr4(addrRel, lookback))
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case opcodes.MODE_IMMEDIATE:
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return fmt.Sprintf("#$%02X ", byte1)
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return fmt.Sprintf("#$%02X", byte1)
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case opcodes.MODE_ABS_X:
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return fmt.Sprintf("$%04X,X", addr16)
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return fmt.Sprintf("%s,X", s.addr4(addr16, lookback))
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case opcodes.MODE_ABS_Y:
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return fmt.Sprintf("$%04X,Y", addr16)
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return fmt.Sprintf("%s,Y", s.addr4(addr16, lookback))
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case opcodes.MODE_ZP:
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return fmt.Sprintf("$%02X ", byte1)
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return fmt.Sprintf("%s", s.addr2(byte1, lookback))
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case opcodes.MODE_ZP_X:
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return fmt.Sprintf("$%02X,X ", byte1)
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return fmt.Sprintf("%s,X", s.addr2(byte1, lookback))
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case opcodes.MODE_ZP_Y:
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return fmt.Sprintf("$%02X,Y ", byte1)
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return fmt.Sprintf("%s,Y", s.addr2(byte1, lookback))
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case opcodes.MODE_INDIRECT_Y:
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return fmt.Sprintf("($%02X),Y", byte1)
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return fmt.Sprintf("(%s),Y", s.addr2(byte1, lookback))
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case opcodes.MODE_INDIRECT_X:
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return fmt.Sprintf("($%02X,X)", byte1)
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case opcodes.MODE_A:
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return " "
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return fmt.Sprintf("(%s,X)", s.addr2(byte1, lookback))
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}
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panic(fmt.Sprintf("Unknown op mode: %d", mode))
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}
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@ -64,19 +98,19 @@ func addrString(pc uint16, byte1, byte2 byte, length int, mode opcodes.Addressin
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// instruction. It returns the formatted bytes, the formatted
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// instruction and address, and the length. If it cannot find the
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// instruction, it returns a 1-byte "???" instruction.
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func Disasm(pc uint16, byte0, byte1, byte2 byte) (string, string, int) {
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func Disasm(pc uint16, byte0, byte1, byte2 byte, s Symbols, lookback int) (string, string, int) {
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op, ok := opcodes.Opcodes[byte0]
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if !ok {
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op = opcodes.NoOp
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}
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length := opcodes.ModeLengths[op.Mode]
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bytes := bytesString(byte0, byte1, byte2, length)
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addr := addrString(pc, byte1, byte2, length, op.Mode)
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addr := addrString(pc, byte1, byte2, length, op.Mode, s, lookback)
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return bytes, op.Name + " " + addr, length
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}
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// DisasmBlock disassembles an entire block, writing out the disassembly.
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func DisasmBlock(block []byte, startAddr uint16, w io.Writer) {
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func DisasmBlock(block []byte, startAddr uint16, w io.Writer, s Symbols, lookback int, printLabels bool) {
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l := len(block)
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for i := 0; i < l; i++ {
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byte0 := block[i]
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@ -89,8 +123,46 @@ func DisasmBlock(block []byte, startAddr uint16, w io.Writer) {
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byte2 = block[i+2]
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}
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addr := uint16(i) + startAddr
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bytes, op, length := Disasm(addr, byte0, byte1, byte2)
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fmt.Fprintf(w, "$%04X: %s %s\n", addr, bytes, op)
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bytes, op, length := Disasm(addr, byte0, byte1, byte2, s, lookback)
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if printLabels {
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label, ok := s[int(addr)]
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if ok {
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fmt.Fprintf(w, "$%04X: %s:\n", addr, label)
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}
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}
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fmt.Fprintf(w, "$%04X: %-8s %s\n", addr, bytes, op)
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i += length - 1
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}
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}
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var symRe = regexp.MustCompile(`(?i)^([0-9a-z_]+) *(?:.eq|equ|epz|=) *\$([0-9a-f]+)\b`)
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func ReadSymbols(filename string) (Symbols, error) {
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file, err := os.Open(filename)
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if err != nil {
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return nil, err
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}
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scanner := bufio.NewScanner(file)
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s := make(Symbols)
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lineNum := 0
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for scanner.Scan() {
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line := scanner.Text()
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lineNum++
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groups := symRe.FindStringSubmatch(line)
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if groups == nil {
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continue
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}
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i, err := strconv.ParseInt(groups[2], 16, 32)
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if err != nil {
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return nil, fmt.Errorf("%d: %s: %s", lineNum, line, err)
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}
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if i > 0xffff {
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return nil, fmt.Errorf("%d: %s: Value %d out of range", lineNum, line, i)
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}
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s[int(i)] = groups[1]
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}
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if err := scanner.Err(); err != nil {
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return nil, err
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}
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return s, nil
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}
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26
asm/disasm_test.go
Normal file
26
asm/disasm_test.go
Normal file
@ -0,0 +1,26 @@
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package asm
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import "testing"
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func TestSymbolRE(t *testing.T) {
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tests := []struct {
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line string
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label string
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address string
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}{
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{"SHAPEL EQU $1A POINTER TO", "SHAPEL", "1A"},
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}
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for i, tt := range tests {
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groups := symRe.FindStringSubmatch(tt.line)
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if groups == nil {
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t.Errorf(`%d. Unable to parse '%s'`, i, tt.line)
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}
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if groups[1] != tt.label {
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t.Errorf(`%d. want label='%s'; got '%s' for line: '%s'`, i, tt.label, groups[1], tt.line)
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}
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if groups[2] != tt.address {
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t.Errorf(`%d. want address='%s'; got '%s' for line: '%s'`, i, tt.address, groups[2], tt.line)
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}
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}
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}
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@ -132,7 +132,7 @@ func (c *cpu) Reset() {
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// status prints out the current CPU instruction and register status.
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func status(c *cpu, m Memory) string {
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bytes, text, _ := asm.Disasm(c.PC(), m.Read(c.PC()), m.Read(c.PC()+1), m.Read(c.PC()+2))
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return fmt.Sprintf("$%04X: %s %s A=$%02X X=$%02X Y=$%02X SP=$%02X P=$%08b",
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return fmt.Sprintf("$%04X: %-8s %-11s A=$%02X X=$%02X Y=$%02X SP=$%02X P=$%08b",
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c.PC(), bytes, text, c.A(), c.X(), c.Y(), c.SP(), c.P())
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}
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