For a CTF I have a fairly slow recursive function. I just need to cached the previous results in a dictionary and get them instead. I did it but had to reverse engineer the code. I was wondering if there is a better solution.

LD_PRELOAD won't work as it is a static binary. If I could copy the assembly and call the function in a C program with asm I could get it done but is there a better solution or a way to patch the binary and create a function that caches the slow one? We could path the binary or use somethings to hook the function call.

1 Answer 1


You can definitely edit the binary and implement a new function that handles caching and calls the original function as needed. Then just replace any call to your new cache-implementing function instead. You'll need to be careful when implementing the cache for a recursive function and decide if you wanna cache all intermediate results or only final results.

If you're looking for a fast solution, though, you may want to consider using an emulator as a way of running that function's code inside your program. Either using Unicorn, any other emulator or even IDAs app call for function execution.

  • 1
    Thank you very much you got me on the right track. The easiest solution was to use Unicorn. I tried a lot and the other reasonable one was frida but I have yet to manage to get it working. This link helped me a lot: http://eternal.red/2018/unicorn-engine-tutorial/
    – letFunny
    Feb 27, 2019 at 9:43
  • Glad I could help :)
    – NirIzr
    Feb 27, 2019 at 10:02

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