Frida JIT example

jit-example.js

'use strict';

const slowCallback = new NativeCallback(value => {
  console.log('slowCallback hit');
  return 43;
}, 'int', ['int']);

const fastCallback = Memory.alloc(Process.pageSize);
Memory.patchCode(fastCallback, 128, code => {
  const cw = new X86Writer(code, { pc: fastCallback });
  cw.putCmpRegI32('edi', 10);
  cw.putJccShortLabel('je', 'match', 'unlikely');

  cw.putLabel('nomatch');
  cw.putMovRegU64('rax', 42);
  cw.putJmpShortLabel('done');

  cw.putLabel('match');
  cw.putSubRegImm('rsp', 8);
  cw.putCallAddressWithAlignedArguments(slowCallback, ['edi']);
  cw.putAddRegImm('rsp', 8);

  cw.putLabel('done');
  cw.putRet();

  cw.flush();
});

const cb = new NativeFunction(fastCallback, 'int', ['int']);
for (let i = 0; i !== 100; i++) {
  const result = cb(i)
  console.log(`${i} => ${result}`);
}