CE Tutorial - How to find __fastcall function parameters in 64 bit process and call it

Zenbeau · Post by **Zenbeau** » Mon Aug 31, 2026 7:27 am

in this video, we call the Give Weapon function in GTA 3 to give ourselves any weapon.

how do i know i'm looking at a __fastcall? since this is a 64-bit application, it natively uses the x64 calling convention, which is based on __fastcall. it's a 64-bit process, 99% of them are gonna be __fastcalls. i was calling it the standalone give weapon function, but LibertyCity.exe+10D5B00 can also be known as the give weapon 'helper function'.

GTA 3 weapon modding resource: https://wiki.gtaconnected.com/Resources/GTA3/Weapons

script for Give Weapon:

Code: Select all

[ENABLE]
alloc(GiveWeapon, 2048)
CreateThread(GiveWeapon)
registersymbol(GiveWeapon)

GiveWeapon:
  sub rsp, 28  // allocate 40 bytes shadow space

  mov rcx,["LibertyCity.exe"+4D9FC88] // player base/localplayer pointer
  mov rdx, #6  // weapon ID
  mov r8, #250  // ammo

  call LibertyCity.exe+10D5B00

  // clean up stack frame and exit thread
  add rsp, 28
  ret

[DISABLE]
unregistersymbol(GiveWeapon)
dealloc(GiveWeapon)