8000 Multi-line arguments in a function call crashes CPython · Issue #101928 · python/cpython · GitHub
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xiaxinmeng opened this issue Feb 15, 2023 · 4 comments
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Multi-line arguments in a function call crashes CPython #101928

xiaxinmeng opened this issue Feb 15, 2023 · 4 comments
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3.12 only security fixes interpreter-core (Objects, Python, Grammar, and Parser dirs) release-blocker type-crash A hard crash of the interpreter, possibly with a core dump

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@xiaxinmeng
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xiaxinmeng commented Feb 15, 2023 •
edited by bedevere-bot
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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
@xiaxinmeng xiaxinmeng added the type-crash A hard crash of the interpreter, possibly with a core dump label Feb 15, 2023
@xiaxinmeng xiaxinmeng changed the title Multi-line arguments in function call crashes CPython Multi-line arguments in a function call crashes CPython Feb 15, 2023
@ronaldoussoren ronaldoussoren added the interpreter-core (Objects, Python, Grammar, and Parser dirs) label Feb 15, 2023
@hauntsaninja
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Thanks for the report! I bisected this to #101633 cc @penguin-wwy @iritkatriel

@kumaraditya303 kumaraditya303 added 3.12 only security fixes release-blocker labels Feb 15, 2023
@iritkatriel
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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.

@bedevere-bot bedevere-bot mentioned this issue Feb 15, 2023
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@penguin-wwy
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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.

iritkatriel pushed a commit that referenced this issue Feb 16, 2023
@penguin-wwy
gh-101928: fix crash in compiler on multi-line lambda in function call (
df7ccf6 
#101933)
@iritkatriel
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Thanks for the report @xiaxinmeng, and for the fix @penguin-wwy .

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