Multi-line arguments in a function call crashes CPython

Crash report

In a function call, if one argument is split in two lines, CPython crashes. For example, we split the lambda expression, i.e., lamda_exp=lambda:1, in test2.py into two lines (See test1.py) . CPython reports a segmentation fault.

This crash just occurs on the latest main branch(e.g.commit a1f08f5, 8a2b7ee ). The older version of CPython(e.g. CPython 3.10.8, CPython 3.9.0 ) does not report any crash.

test1.py (Segmentation fault)

def foo(param, lambda_exp):
    pass

foo(param=0,
    lambda_exp=lambda:
    1)

test2.py (work well )

def foo(param, lambda_exp):
    pass

foo(param=0,
    lambda_exp=lambda:1)

Error messages

Segmentation Fault

Your environment

CPython versions tested on: main branch from GitHub (commit a1f08f5)
Operating system and architecture: Ubuntu 18.04

Linked PRs

gh-101928: fix crash in compiler on multi-line lambda in function call #101933

@penguin-wwy

Thanks for the report! I bisected this to #101633 cc @penguin-wwy @iritkatriel

@hauntsaninja

Thank you @hauntsaninja.

I see the problem - we are now creating a basicblock with

RETURN_CONST followed by NOP, and the redundant NOP is not being removed before propagate_line_numbers() uses BB_HAS_FALLTHROUGH on the block, which only looks at the last instruction to see if it exits the block.

Possible fixes:

(easiest) replace LOAD_CONST, RETURN_VALUE by NOP, RETURN_CONST (instead of RETURN_CONST, NOP).
make sure the redundant NOP is removed before propagate_line_numbers is called

I'll fix it tomorrow if nobody else will beat me to it.

@hauntsaninja

Thank you @hauntsaninja.

I see the problem - we are now creating a basicblock with

RETURN_CONST followed by NOP, and the redundant NOP is not being removed before propagate_line_numbers() uses BB_HAS_FALLTHROUGH on the block, which only looks at the last instruction to see if it exits the block.

Possible fixes:
1. (easiest) replace LOAD_CONST, RETURN_VALUE by NOP, RETURN_CONST (instead of RETURN_CONST, NOP).

2. make sure the redundant NOP is removed before propagate_line_numbers is called
I'll fix it tomorrow if nobody else will beat me to it.

@iritkatriel Thanks for the fix suggestion, I tried to fix it using the first method and it seems to have minimal impact and is effective.

gh-101928: fix crash in compiler on multi-line lambda in function call (

@xiaxinmeng

Thanks for the report @xiaxinmeng, and for the fix @penguin-wwy .

Navigation Menu

Repository navigation

Multi-line arguments in a function call crashes CPython #101928

Crash report

Error messages

Your environment

Linked PRs

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Multi-line arguments in a function call crashes CPython #101928

Description

Crash report

Error messages

Your environment

Linked PRs

Activity

hauntsaninja commented on Feb 15, 2023

iritkatriel commented on Feb 15, 2023

penguin-wwy commented on Feb 15, 2023

iritkatriel commented on Feb 16, 2023

Metadata

Metadata

Assignees

Labels

Projects

Milestone

Relationships

Development

Issue actions