---
tags: comp-decomp
title: Slicing Instructions corpus
---

# Overview

This experiment analyzes the information gained from slicing code objects to see what instructions are discovered.

## Slicing assumptions

All Code Object slices have the following properties.
- Python version: 3.8
- All slices don't start with:
- `STORE_FAST`
- `JUMP_ABSOLUTE`
- Update jumps if the target of the jump is within the slice region
- Update Jump instructions to last instruction if greater than last offset of slice.
- Append `RETURN_VALUE` instruction to preserve nature of the code object

:::info
Our slice will also contain the original code object .i.e. decompilation of the code object.
:::

## Code examples:

All code examples are motivated by changing control flows from [here](https://hackmd.io/Pnoy0j14Qy2172yNDlYF2A?both)

### Example 1:
Original code:

while a or b:
       continue

Decompilation:

while not a:
    if b:
        continue

Instructions from slicing:

{
'return', 
'while not a:', 
'    if b:', 
'        continue', 
'    pass', 
'if b:'
}

### Example 2:
Original code:

while a or b or c and d:
    continue
z=z

Decompilation:

while not a:
    if not b:
        if c:
            if d:
                continue

z = z

Instructions from slicing:

{
'    pass', 
'            pass', 
'if not b:', 
'if d:',
'while not a:', 
'        if c:', 
'                continue', 
'if c:', 
'            if d:', 
'    if c:', 
'    if d:', 
'z = z', 
'return', 
'        if d:', 
'        pass', 
'    if not b:'
}

:::warning
Might use PyFET for more diverse inputs.
:::

### Example 3:
Original code:

for item in token_generator:
    tmp = a and b
    if tmp:
        if c or d or e :
            z = z 
    else:
        z = z

Decompilation:

for item in token_generator:
    tmp = a and b
    if not tmp or c or d or e: # This is incorrect
        z = z
    else:
        z = z

Instructions from slicing:

{
'            z = z', 
'    else:', 
'if not c:', 
'tmp = b', 
'tmp = a and b', 
'    if not tmp or c or d or e:', 
'                if e:', 
'        if c or d or e:', 
'if not d:', 
'    pass', 'if tmp:', 
'        if not d:', 
'        pass', 
'                    pass', 
'                pass', 
'z = z', 
'            if not d:', 
'        if not c:', 
'    if not d:', 
'            if e:', 
'if e:', 
'for item in token_generator:', 
'    tmp = a and b', 
'        if e:', 
'    if tmp:', 
'    if not c:', 
'            pass', 
'    if e:', 
'        z = z', 
'return'
}

### Example 4:
Original code:

def nextUid():
    try:
        pass
    except z:
        raise 'errr'
    return x

Decompiled code:

def nextUid():
    try:
        pass
    except z:
        raise 'errr'
    else:
        return x

Instructions from slicing:

{
"    raise 'errr'", 
'try:', 
'return x', 
"raise 'errr'", 
'    return x', 
'except z:', 
'    pass', 
'else:'
}