Not sure how to handle Assembly in Doom 1

Memory scanning, code injection, debugger internals and other gamemodding related discussion
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denismu
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Not sure how to handle Assembly in Doom 1

Post by denismu »

Hi there,

I am trying on a cheat for Doom 1.
Now the good thing is I guess I know, that Doom 1 has coded
two locations for health.

One is => sub [edi+20],ebx
that is the one where it subtracts the value of health as seen.

The second is => sub [esi+6c],eax or similar, but when I replace it with code
that does nothing, the enemies are invulnerable too.

Does anyone know of a workaround or some tutorial, where I could learn to
handle this ? :mellow:

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EpicBirdi
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Re: Not sure how to handle Assembly in Doom 1

Post by EpicBirdi »

Check out some guides on "Shared Opcodes" -- instructions that write to multiple addresses.
The idea is basically to find something unique to the player and generally only do your new, cheaty instruction when it is the player.

The CE tool you need is the commonality scanner (dissect structure).

If you need hands-on help, feel free to contact me on Discord. I'll be free on Wednesday.

denismu
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Re: Not sure how to handle Assembly in Doom 1

Post by denismu »

Hey thank you very much for the reply.
I figured it out ,just like you said.
Find a piece of code in memory via the structure dissection and
put it into assembly when it should get executed.
I just used a cmp instruction to that end, and .... it works.
Thank you again for offering your help to me.

I will try to add you in Discord.

bye,

Denis.

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