New submission from Rok Mandeljc <[email protected]>:
dis module incorrectly handles the instruction sequence where EXTENDED_ARG is
followed by NOP, e.g.,:
EXTENDED_ARG 0x01
NOP
EXTENDED_ARG 0x01
LOAD_CONST 0x29
The above sequence loads the constant from index 0x0129, whereas dis attempts
to load it from index 0x010129, resulting in "IndexError: tuple index out of
range error" when attempting to iterate over instructions returned by
dis.get_instructions().
Complete example:
# *** example.py begin ***
import types
import dis
# Create a test code object...
constants = [None] * (0x000129 + 1)
constants[0x000129] = "Hello world!"
code = types.CodeType(
0, # argcount
0, # posonlyargcount
0, # kwonlyargcount
0, # nlocals
1, # stacksize
64, # flags
bytes([
0x90, 0x01, # EXTENDED_ARG 0x01
0x09, 0xFF, # NOP 0xFF
0x90, 0x01, # EXTENDED_ARG 0x01
0x64, 0x29, # LOAD_CONST 0x29
0x53, 0x00, # RETURN_VALUE 0x00
]), # codestring=
tuple(constants), # constants
(), # names
(), # varnames
'<no file>', # filename
'code', # name
1, # firstlineno
b'' # linetable
)
# ... and eval it to show that NOP resets EXTENDED_ARG
print("Output:", eval(code))
# Try to list all instructions via dis
print(list(dis.get_instructions(code)))
# *** example.py end ***
Running the example gives us:
Output: Hello world!
Traceback (most recent call last):
File "/home/rok/example.py", line 35, in <module>
print(list(dis.get_instructions(code)))
File "/usr/lib64/python3.10/dis.py", line 338, in _get_instructions_bytes
argval, argrepr = _get_const_info(arg, constants)
File "/usr/lib64/python3.10/dis.py", line 292, in _get_const_info
argval = const_list[const_index]
IndexError: tuple index out of range
To fix the problem on dis side, the extended_arg in dis._unpack_opargs should
be reset to 0 when NOP (or perhaps any opcode without argument) is encountered.
I.e., by adding "extended_arg = 0" here:
https://github.com/python/cpython/blob/91275207296c39e495fe118019a757c4ddefede8/Lib/dis.py#L525
The problematic behavior was reported by users of PyInstaller under python
3.10; it seems that python 3.10 generates bytecode involving EXTENDED_ARG + NOP
for telegram.message.py:
https://raw.githubusercontent.com/python-telegram-bot/python-telegram-bot/v13.7/telegram/message.py
The original PyInstaller issue with preliminary analysis is here:
https://github.com/pyinstaller/pyinstaller/issues/6301
----------
components: Library (Lib)
messages: 405985
nosy: rok.mandeljc
priority: normal
severity: normal
status: open
title: dis module incorrectly handles EXTENDED_ARG + NOP sequence
type: behavior
versions: Python 3.10, Python 3.8, Python 3.9
_______________________________________
Python tracker <[email protected]>
<https://bugs.python.org/issue45757>
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