kmips

kmips is a MIPS assembler that is invoked directly from Kotlin code. It implements MIPS II instruction set, including FPU (coprocessor 1) instructions. The main purpose of kmips is to provide simple way of writing code patches for compiled executables. It was successfully used in few fan translations and game modding projects.

kmips is available from the Maven Central repository:

implementation "com.kotcrab.kmips:kmips:1.7"

Example code

Assemble some instruction to fill 32 bytes of memory at address 0x08804100 with incrementing value

import kmips.Label
import kmips.Reg.*
import kmips.assemble

assemble(startPc = 0x8804000) {
  val loop = Label()
  val target = 0x08804100
  val bytes = 32

  la(s0, target)     // write target address
  li(t1, 0)          // loop counter
  li(t2, bytes)      // how many bytes to write
  label(loop)        // 'loop' label will be placed here
  sb(t1, 0, s0)      // store byte in memory at register s0 with offset 0
  addiu(t1, t1, 1)   // increment loop counter
  addiu(s0, s0, 1)   // increment memory address pointer
  bne(t1, t2, loop)  // jump to `loop` branch if not equal
  nop()              // ignoring branch delay slot for example simplicity
}

Result of running the assembled code:

0x08804100: 00 01 02 03 | 04 05 06 07 | 08 09 0A 0B | 0C 0D 0E 0F
0x08804110: 10 11 12 13 | 14 15 16 17 | 18 19 1A 1B | 1C 1D 1E 1F

Specifying startPc (initial program counter) is necessary for calculating address of branch and jump instructions.

Alternatively to assemble which returns a List<Int> you can also use assembleAsHexString or assembleAsByteArray. In any case, the result is ready to be written into the target executable. If you're executable is relocatable you might also need to manually update relocation table.