Help Modify a boolean in a Game Boy ROM

[JokerTheTrickster]

Is it possible to modify a Boolean variable in a Gameboy ROM using a hexadecimal editor? What would that be? Do you have any tips?

 

[Goshikk]

this question is a bit confusing. how do you know which variable it is and where in the rom it's sitting?
by the time you can answer that, i figure it should be a bit easier to change whichever variables you please...

 

[JokerTheTrickster]

this question is a bit confusing. how do you know which variable it is and where in the rom it's sitting?
by the time you can answer that, i figure it should be a bit easier to change whichever variables you please...

Oh well, I'm creating something in GB Studio, But my question is whether someone else could modify it using the hexadecimal code.

 

[Goshikk]

if you're worried about someone hacking your game, yes, someone else could disassemble your game and modify it
although i find it unlikely that anyone would care enough to do that

otherwise i have no idea what you're talking about. can't you just edit it in gb studio

 

[JokerTheTrickster]

if you're worried about someone hacking your game, yes, someone else could disassemble your game and modify it
although i find it unlikely that anyone would care enough to do that

otherwise i have no idea what you're talking about. can't you just edit it in gb studio

Well, my intention was for someone to modify it, similar to Ghaster in Undertale

 

[qw90700]

Sure.

- You need to debug GBA game to see what changes when whatever you want it to happen changes. For example which part of the memory having the value "00" when for example you cannot save and what value that byte have when you can save.

- I never hacked a GBA game before but I did when it comes to PC, PS1 and PS2 games. I can say boolean logic not always simply "00" or "01" as off and on flags. But the logic is it is usually "the byte having the least value to mean off and having higher value to mean on". So for a game "01" may mean "off" and "FF" may mean on or "0A" means off and "0B" means on, sometimes 02 can mean off while 04 means on or something. You gotta check how whatever you wanna change is.

- Some things are not simply function via a boolean logic. For example which party members available to you or not in RPG games doesn't have to be flagged via a boolean.

- Debuggers helps you to analyze assembly code when turn on and off flags you looking for triggered. Thus you can find where in the rom these code came from to trace them back in the rom to find these values you wanna change.

- A boolean value may be a byte or a bit. Pay attention to that. Sometimes a game may use same byte space for its individual 2 bit to make some different stuff happen, that's why you may change turn on and off state of whatever you want as a byte but if the logic function via bit you may break the game.

- It may seem like boolean because all you see is a difference between 00 and 01 but in reality it may be an assembly code instead of boolean. If that's the case simply byte/bit editting won't work, you gotta properly change the assembly code of the rom via studying how the game works.

- We talking about a GBA game, and it means developers may used heavy optimizations to ease CPU's work and save RAM space by using same byte/bits for different core logic of the game. So what you looking for may be boolean but if that's the case changing it can crash the game by breaking natural flow of the expected processing of pre-determined codes. To avoid it (if it happens) you would have to reverse engineer GBA and how the game works to make the change by re-writing that part of the game according to whatever you wanna change even if it is simple on/off flag change.

- How codes work?: They work like a music. It means each piece of code must be in harmony with what came before it so according to how code was flowing the next codes should befit to the bigger picture. That's why sometimes a simple edit is not a simply done via byte/bit change, so whatever you wanna change in the game just to avoid crash and actually make it happen you may have to change the whole code of that system. If it is being able to save or not you may have to change any code related to keeping player to always able to save instead of being in particular locations. If it's about enabling party members you may have to change what triggers enabling party members and all.

To not break natural way of how games' code work and avoid writing entire system for it you may use advanced assembly hacking methods if the new added value floods to other parts of the code and making the game doesn't function properly. One method is changing which location the game looks for the flag code and you carry the flag code to an "empty zone" in the rom that there is code nowhere near it. If you cannot find "empty zone" you can create one at the end of rom's data but you gotta follow how to expand data space of rom for a GBA game.

Well, my intention was for someone to modify it, similar to Ghaster in Undertale

Then you may add anti-cheat measurements by tying tons of "if X is this value make Y, Z, L happen" flags and checks so for example whole game can work just because player cannot save the game so it's turned off as "00" so if a hacker try to make it "01" whole game crashes so hacker cannot simply change and call it a day lol.

So all you can do is making the hacker realize to make a simple change you gotta change most of the game, but then what matter is why you care people cheating their way in your game anyway.

 

[Goshikk]

Well, my intention was for someone to modify it, similar to Ghaster in Undertale

I see. You mean the fun value.
What you want is a way to make the SRAM file editable so that your desired outcome happens.
Maybe make a separate tool that tinkers with just that?
Asking users to hex edit the base rom is just asking for disaster lol