[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Victor Milovanov]

Victor Milovanov  added the comment:

A bit more information: pool->freeblock for the broken pool looks like this:
0xXYZ?
while pool itself looks like this:
0x??XYZ000

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Victor Milovanov]

Victor Milovanov  added the comment:

In my case it always happens in pymalloc_alloc when size == 5, e.g. when 
accessing usedpools[10].
Specifically freeblock pointer in usedpools[10] is wy off (essentially, 
seemingly random number looking like 0xX000) where it is supposed to be 
(e.g. very far from usedpools[10]). Surprisingly, all the other fields in 
usedpool[10] seem to have normal values.

I could not find any place in obmalloc.c where this value would be set, so it 
seems to be a memory corruption caused by something else.

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Victor Milovanov]

Victor Milovanov  added the comment:

This reproduces stably for me when running unit tests in Python.NET project at 
commit 5e276d9.

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nosy: +Victor Milovanov

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Mark Inderhees]

Mark Inderhees  added the comment:

Correction to my previous post. I did use capital X, ie '-X dev'.

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Mark Inderhees]

Mark Inderhees  added the comment:

I have reproduced this with both PYTHONMALLOC=debug and "py -3.7 -x dev ", but it did not print out any allocation debug info. When using this 
option, it does take many more attempts to hit the issue than if running 
without debugging turned on.

Is there some other useful info I can gather?

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[STINNER Victor]

STINNER Victor  added the comment:

Try to reproduce your bug using PYTHONMALLOC=debug environment variable:
https://pythondev.readthedocs.io/debug_tools.html#memory-debugger

On Python 3.7, you can use "py -3.7 -X dev program.py" (-X dev option) to 
enable PYTHONMALLOC=debug.

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[issue35235] Access violation on alloc in Windows x86-64 python, pymalloc_alloc

[Mark Inderhees]

Mark Inderhees  added the comment:

Actually, I have now seen this in full installed python. I have updated the 
title.

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title: Access violation on alloc in Windows x86-64 embeddable python, 
pymalloc_alloc -> Access violation on alloc in Windows x86-64 python, 
pymalloc_alloc

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