public static ObjectCodeHeader ReadObjectCodeHeader(byte[] objectCode)
{
var header = new ObjectCodeHeader();
using (var br = new BinaryReader(new MemoryStream(objectCode)))
{
int hasEntryPoint = br.ReadInt32();
int entryPointFunctionLabel = br.ReadInt32();
int numRelocations = br.ReadInt32();
int numLabels = br.ReadInt32();
int numSymbols = br.ReadInt32();
int dataOffset = br.ReadInt32();
header.DataStart = dataOffset;
header.SizeOfDataAndCode = (int)br.BaseStream.Length - dataOffset;
header.HasEntryPoint = hasEntryPoint == 1;
header.EntryPointFunctionLabel = entryPointFunctionLabel;
//Read relocations
header.RelocationAddresses = new List <int>();
for (int i = 0; i < numRelocations; i++)
{
header.RelocationAddresses.Add(br.ReadInt32());
}
//Read label addresses
header.LabelAddresses = new List <LabelAddressTableEntry>();
for (int i = 0; i < numLabels; i++)
{
int type = br.ReadInt32();
switch (type)
{
case 0: //null entry
header.LabelAddresses.Add(null);
br.ReadInt32();
break;
case 1: //internal address
header.LabelAddresses.Add(
new LabelAddressTableEntry()
{
Index = i,
IsExtern = false,
Address = br.ReadInt32()
}
);
break;
case 2: //external symbol
header.LabelAddresses.Add(
new LabelAddressTableEntry()
{
Index = i,
IsExtern = true,
SymbolName = br.ReadString()
}
);
break;
}
}
//Read exported symbols
header.ExportedSymbols = new Dictionary <string, int>();
for (int i = 0; i < numSymbols; i++)
{
string name = br.ReadString();
int labelNum = br.ReadInt32();
header.ExportedSymbols.Add(name, labelNum);
}
}
return(header);
}
public static void WriteObjectFileHeader(ObjectCodeHeader header, BinaryWriter bw)
{
//Label address table
byte[] labelAddressTableData;
using (var stream = new BinaryWriter(new MemoryStream()))
{
if (header.LabelAddresses.Count > 0)
{
for (int i = 0; i < header.LabelAddresses.Max(a => a.Index) + 1; i++)
{
var addressRow = header.LabelAddresses.FirstOrDefault(a => a.Index == i);
if (addressRow == null)
{
stream.Write(0); //type
stream.Write(0); //value
}
else
{
if (addressRow.IsExtern)
{
stream.Write(2); //type
stream.Write(addressRow.SymbolName);
}
else
{
stream.Write(1);
stream.Write(addressRow.Address);
}
}
}
}
labelAddressTableData = ((MemoryStream)stream.BaseStream).ToArray();
}
//Symbol table
byte[] symbolTableData;
using (var stream = new BinaryWriter(new MemoryStream()))
{
foreach (var exportedSymbol in header.ExportedSymbols)
{
stream.Write(exportedSymbol.Key);
stream.Write(exportedSymbol.Value);
}
symbolTableData = ((MemoryStream)stream.BaseStream).ToArray();
}
//Compute offsets
int relocationsOffset = 24;
int labelsOffset = relocationsOffset + (header.RelocationAddresses.Count * 4);
int symbolTableOffset = labelsOffset + labelAddressTableData.Length;
int dataOffset = symbolTableOffset + symbolTableData.Length;
//Offset values
bw.Write(header.HasEntryPoint ? 1 : 0);
bw.Write(header.EntryPointFunctionLabel);
bw.Write(header.RelocationAddresses.Count); //# relocations
if (header.LabelAddresses.Count > 0)
{
bw.Write(header.LabelAddresses.Max(a => a.Index) + 1); //# labels
}
else
{
bw.Write(0);
}
bw.Write(header.ExportedSymbols.Count); //# symbols
bw.Write(dataOffset); //where data section starts
//Relocation addresses
foreach (int loc in header.RelocationAddresses)
{
bw.Write(loc);
}
//Label addresses
bw.Write(labelAddressTableData, 0, labelAddressTableData.Length);
//Symbol table
bw.Write(symbolTableData, 0, symbolTableData.Length);
}
