This way we’ll be able to retrieve it later. When we use a command like sw ra, 0x14 (sp) that has a register in parentheses, we are using the immediate as an offset to that register, so this saves the return address 0x14 half-bytes (20 in base ten) after the stack pointer’s memory address. Since this is ASM and everything has to be difficult, we must allocate our own memory on the stack for any variables we want to preserve between function calls by incrementing the stack pointer, especially the return address which allows the program to return to whichever function called the function we’re currently executing. Let’s start with the bread and butter of functions:įunctions in ASM all pretty much start the same way, with a addiu sp, sp command and a sw ra, (sp). Proc802CB1C0_end: lw ra, 0x14 (sp) jr ra addiu sp, sp, 0x18. Li t0, MARIO_STRUCT li t1, ACTION_JUMP sw t1, 0x0C(t0) Set mario’s action to jumping. Tests if the player is holding down the L button.f_testInput BUTTON_L, BUTTON_PRESSED, proc802CB1C0_end orga 0x861C0 Set ROM address, we are overwritting a useless loop function as our hook.area 0xA4 Set data import limit to 0xA4 bytes addiu sp, sp, -0x18 sw ra, 0x14 (sp) When the player holds the L button, Mario will float up into the air
#Super mario 64 last impact injected wad code
We’ll be looking at an example that overrides a debug function (it does nothing, but the code calls it anyway) to allow the player to jump override any state to jumping by pressing L: Now, let’s see what injecting a custom function looks like. So, if we swap it out for a BEQZ we should be able to walljump on parallel walls! Which branches on perpendicular wall collision it’s the part of the code that gives the player the opportunity to walljump on perpendicular walls. One interesting place to apply this is the code line 80256498 As you might expect, we can use this to negate a BEQZ command. This command does the opposite of BEQZ: BNEZ stands for “Branch on Not Equal to Zero”.
A more complete list of ASM commands can be found here.Īnother related command is the BNEZ command. So, if T3 = 00000000 801A6BC0, BEQZ T3 will fail to jump to its immediate location, and execute the next instruction as normal.
Finally, the last hexidecimal immediate argument for a BEQZ command represents the location in code to jump to should the comdition be met. T3 can be seen on the list of registers on the right of the debugger: its value in the image is 00000000 801A6BC0, a hexidecimal number.
So what is it’s argument? Why, it’s the register T3, which is a place a temporary value can be stored by the computer for math and logic operations. It’s part of a family of commands called branch commands that examine some condition and jump to somewhere else in the code if it’s true BEQZ does this if its argument is zero. The command BEQZ stands for “Branch on EQual to Zero”. Since conventional decimal runs out of digits at 9, we start using English letters. Hexidecimal is a base 16 number system useful in computing because a single digit can represent 4 of the computer’s ones and zeros in binary (2⁴ = 16).
#Super mario 64 last impact injected wad series
ASM takes the form of a series of cryptic abbreviated commands, followed by a combination of 2 digit alpha-numeric registers and hexidecimal immediate values. The right side of the debugger shows a line by line view of each ASM command and its arguments as disassembled by the debugger.
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