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WasmReaderBase.cs
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WasmReaderBase.cs
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using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using NameMap = System.Collections.Generic.Dictionary<System.UInt32, string>;
namespace WebAssemblyInfo
{
public abstract class WasmReaderBase
{
public readonly BinaryReader Reader;
public UInt32 Version { get; private set; }
public string Path { get; private set; }
protected readonly long Length;
protected readonly Stack<long> EndOfModulePositions = new();
public WasmReaderBase(string path)
{
if (Program.Verbose)
Console.WriteLine($"Reading wasm file: {path}");
Path = path;
var stream = File.Open(Path, FileMode.Open);
Length = stream.Length;
Reader = new BinaryReader(stream);
EndOfModulePositions.Push(Length);
}
public WasmReaderBase(Stream stream, long len)
{
Length = len;
Path = "[embedded]";
Reader = new BinaryReader(stream);
EndOfModulePositions.Push(stream.Position + len);
}
public void Parse()
{
ReadModule();
PostParse();
}
protected virtual void PostParse() { }
protected byte[] MagicWasm = { 0x0, 0x61, 0x73, 0x6d };
protected bool InWitComponent = false;
protected virtual void ReadModule()
{
var magicBytes = Reader.ReadBytes(4);
for (int i = 0; i < MagicWasm.Length; i++)
{
if (MagicWasm[i] != magicBytes[i])
throw new FileLoadException("not wasm file, module magic is wrong");
}
Version = Reader.ReadUInt32();
if (Program.Verbose)
Console.WriteLine($"WebAssembly binary format version: 0x{Version:x8}");
switch (Version)
{
case 0x1000d:
InWitComponent = true;
goto case 1;
case 1:
ReadWasmModule();
break;
default:
throw new FileLoadException($"Unsupported WebAssembly binary format version: 0x{Version:x8}");
}
}
void ReadWasmModule()
{
while (Reader.BaseStream.Position < EndOfModulePositions.Peek())
ReadSection();
}
protected enum SectionId
{
Custom = 0,
Type,
Import,
Function,
Table,
Memory,
Global,
Export,
Start,
Element,
Code,
Data,
DataCount,
Tag,
// Wit Component sections
WitCoreCustom = 0x1000,
WitCoreModule,
WitCoreInstance,
WitCoreType,
WitComponent,
WitInstance,
WitAlias,
WitType,
WitCanon,
WitStart,
WitImport,
WitExport,
WitValue,
}
protected struct SectionInfo
{
public SectionId id;
public UInt32 size;
public long offset;
public long begin;
}
protected List<SectionInfo> sections = new();
protected Dictionary<SectionId, List<SectionInfo>> sectionsById = new();
protected abstract void ReadSection(SectionInfo section);
SectionId ReadSectionId()
{
var id = (int)Reader.ReadByte();
if (InWitComponent)
id += 0x1000;
return (SectionId)id;
}
void ReadSection()
{
var section = new SectionInfo() { offset=Reader.BaseStream.Position, id = ReadSectionId(), size = ReadU32(), begin = Reader.BaseStream.Position };
sections.Add(section);
if (!sectionsById.ContainsKey(section.id))
sectionsById[section.id] = new List<SectionInfo>();
sectionsById[section.id].Add(section);
if (Program.Verbose)
Console.Write($"Reading section: {section.id,9} size: {section.size,12}");
ReadSection(section);
if (Program.Verbose)
Console.WriteLine();
Reader.BaseStream.Seek(section.begin + section.size, SeekOrigin.Begin);
}
public UInt32 ReadU32()
{
UInt32 value = 0;
var offset = 0;
do
{
var b = Reader.ReadByte();
value |= (UInt32)(b & 0x7f) << offset;
if ((b & 0x80) == 0)
break;
offset += 7;
} while (true);
return value;
}
protected Int32 ReadI32()
{
Int32 value = 0;
var offset = 0;
byte b;
do
{
b = Reader.ReadByte();
value |= (Int32)(b & 0x7f) << offset;
if ((b & 0x80) == 0)
break;
offset += 7;
} while (true);
if (offset < 32 && (b & 0x40) == 0x40)
value |= (~(Int32)0 << offset);
return value;
}
protected Int64 ReadI64()
{
Int64 value = 0;
var offset = 0;
byte b;
do
{
b = Reader.ReadByte();
value |= (Int64)(b & 0x7f) << offset;
if ((b & 0x80) == 0)
break;
offset += 7;
} while (true);
if (offset < 64 && (b & 0x40) == 0x40)
value |= (~(Int64)0 << offset);
return value;
}
}
}