// Disassemble a game module (sacred2.exe, s2logic.dll, ...) at a virtual
// address (as in Ghidra: the module's preferred image base), independent of
// Ghidra's function boundaries (useful for code only reached via pointers).
//
//   node tools/disasm.mjs <module> <va> [count=60]
//
// Stops after `count` instructions or at the first RET/INT3 run, whichever
// comes later than 8 instructions.

import { readFileSync } from "node:fs";
import { Decoder, DecoderOptions, Formatter, FormatterSyntax, Mnemonic } from "iced-x86";

const [exePath, vaText, countText = "60"] = process.argv.slice(2);
if (!exePath || !vaText) {
  console.error("usage: node disasm.mjs <exe> <va> [count]");
  process.exit(1);
}
const va = Number.parseInt(vaText, 16);
const count = Number.parseInt(countText, 10);

const file = readFileSync(exePath);
const peOffset = file.readUInt32LE(0x3c);
const sectionCount = file.readUInt16LE(peOffset + 6);
const optionalSize = file.readUInt16LE(peOffset + 20);
const imageBase = file.readUInt32LE(peOffset + 24 + 28);
const sectionTable = peOffset + 24 + optionalSize;

function fileOffset(address) {
  const rva = address - imageBase;
  for (let i = 0; i < sectionCount; i++) {
    const s = sectionTable + 40 * i;
    const virtualSize = file.readUInt32LE(s + 8);
    const virtualAddress = file.readUInt32LE(s + 12);
    const rawOffset = file.readUInt32LE(s + 20);
    if (rva >= virtualAddress && rva < virtualAddress + virtualSize) {
      return rawOffset + rva - virtualAddress;
    }
  }
  throw new Error(`address 0x${address.toString(16)} is not in a section`);
}

const start = fileOffset(va);
const bytes = file.subarray(start, start + count * 15);
const decoder = new Decoder(32, bytes, DecoderOptions.None);
decoder.ip = BigInt(va);
const formatter = new Formatter(FormatterSyntax.Intel);
formatter.firstOperandCharIndex = 8;

for (let n = 0; n < count && decoder.canDecode; n++) {
  const instruction = decoder.decode();
  const address = Number(instruction.ip).toString(16).padStart(8, "0");
  const offset = Number(instruction.ip) - va;
  const raw = [...bytes.subarray(offset, offset + instruction.length)]
    .map((b) => b.toString(16).padStart(2, "0"))
    .join(" ");
  console.log(`${address}  ${raw.padEnd(30)} ${formatter.format(instruction)}`);
  instruction.free();
}
decoder.free();
formatter.free();