Help w/ Negative offset pointers

[Sharkbyte]

Do I write negative offset pointers any different than regular po? my address 1 is 810927E0 and address 2 is 8108D8A0. I only get results when I allow a negative offset. I checked one of the best results and found the other memory address and it seems to be responding as health goes down. I have the code as is
48000000 80412918
14000FB8 40800000
E0000000 80008000

with FB8 being a negative offset.

[wiiztec]

It's the same thing as a regular offset cept in the other direction, you subtract from the pointer address value address instead of adding to it, up in memveiwer instead of down

[Sharkbyte]

ok, i noticed that the code isn't working cause the value 40800000 is going down in memory. its executing FB8 farther down in memory even though i know its not supposed to go down in memory. It would work if i could make it go up in memory.

[brkirch]

IIRC there is no code type that directly supports negative offsets, but you can move the pointer value to a Gecko register, subtract the offset (by adding the two's complement of the negative offset) and move the Gecko register value back to po.

Try this:

Code:

82200000 80412918 # Load 80412918 to gr0
86000000 FFFFF048 # Add FFFFF048 to gr0 (Two's complement of -FB8)
4A001000 00000000 # Move gr0 to po
DE000000 80008180 # Checks that po is in the [80000000,81800000] range
66000001 00000000 # Skip next line if the code execution status is set to true
DE000001 90009380 # Endif, then checks that po is in the [90000000,93800000] range
14000000 40800000 # Set 32-bit value at po to 40800000
E0000000 80008000 # Code terminator, reset ba and po to 80000000

This code is untested, so let me know if you have any issues with it.

[Sharkbyte]

You are a genius brkirch! The code works great and doesn't even freeze the wii! I am still kinda new to hacking, but am learning rapidly. Some of those terms are confusing, but i am sure i'll get it 100 percent some day. I have been trying to figure out this code most of the day and couldn't have done it without you! thanks
Post Merge: February 07, 2010, 04:40:18 pmI am just curious, are there other ways to write negative offset operations?

[dcx2]

You could use an asm code type.  C2's require you to hook something, and if that hook isn't called every frame, then you could use a C0, which I think is executed during the code handler.  You'll need two unused registers to do it, but I'm not sure what registers are free during a C0 code (perhaps the code handler pushes all the registers onto the stack before executing C0's?)

This small assembly routine ought to do what you want.  To make it a code, I suggest asmwiird; it does C2 codes, but you can just replace the C2 line with a C0 line.  The only thing left, I think, is that C0's need to end with blr.

Code:

lis r0, 0x8041
ori r0, r0, 0x2918   # load pointer into r0
lis r3, 0x4080       # load value into r3
stw r3,-4024(r0)     # write the value from r3 to the address r0 - 4024
blr                  # terminator for C0 code type

Note that if your value had anything in the lower 16 bits, you would need to use an ori r3, r3, [value], similar to how r0 was loaded with the pointer 0x80412918.