mips[el]32 disassembled from hex input returns missing instructions

[bowserjklol]

I fully recognize I could be doing something wrong so I welcome any pointers...

With this plugin, if you grab some mips32 assembly (you can use some shell code from msf for example):

  li      $t7, -6
  nor     $t7, $t7, $zero
  addi    $a0, $t7, -3
  addi    $a1, $t7, -3
  slti    $a2, $zero, -1
  li      $v0, 4183
  syscall 0x40404
  slt     $s0, $zero, $a3
  bne     $s0, $zero, failed
  sw      $v0, -4($sp) 

Go ahead and assemble it with hex output via the plugin:

Now take that output and push it back through as input and disassemble it into mips mnemonics

It looks like this happens because mips32 (per the docs) has the max_instr_length property set to 8.

the value for mips32 is currently 8 because multiple instructions are decoded looking for delay slots so they can be reordered.

Which the plugin, seemingly correctly, utilizes here:

Shellcoder/__init__.py

Line 81 in cf7045e

instruction_length = len(bv.read(offset, self.arch.max_instr_length))

My workaround has been setting that property to 4 for the sake of outputting mnemonics I'm expecting...

I don't have any great solutions (other API magic in binja to be called?) but wanted to report the issue as you'll probably have a better idea on how best to work around this sanely.

Thanks!