advice on debugging a segfault

Sun Jan 17 16:35:56 EST 2021

I would normally agree, except...

This is a refcount issue (I was able to reproduce the problem, gbd shows a
free error )

And I wouldn't recommend DGBing a refcount issue as a beginner to debugging.

The other mailing list identified a PIL bug that messes up the refcount for
True, but this refcount issue is for some tuple object, so may possibly be
a different problem.

Steve

On Sun, Jan 17, 2021 at 9:27 PM Barry <barry at barrys-emacs.org> wrote:

> Run python under gdb and when the segv  happens use
> the gdb bt command to get a stack trace.
>
> Also if gdb says that it needs debug symbols install you will need to
> do that. Otherwise the not will not contain symbols.
>
> Barry
>
> > On 17 Jan 2021, at 19:58, Robin Becker <robin at reportlab.com> wrote:
> >
> > I have a segfault in the 3.10 alpha 4 when running the reportlab
> document generation; all the other tests seem to have worked. I would like
> to ask experts here how to approach getting the location of the problem. I
> run recent archlinux.
> >
> > Below is the output of  a test run with -Xdev -Xtracemalloc; the main
> process is almost finished so the error appears to come from trying to free
> resources
> >
> >> $ python -Xdev -Xtracemalloc genuserguide.py
> /home/robin/devel/reportlab/.py310/lib/python3.10/distutils/__init__.py:1:
> DeprecationWarning: the imp module is deprecated in favour of importlib;
> see the module's documentation for alternative uses
> >>  import imp
> >> Built story contains 1843 flowables...
> >> Saved
> "/home/robin/devel/reportlab/REPOS/reportlab/docs/reportlab-userguide.pdf"
> >> [ Top 10 ]
> >> <frozen importlib._bootstrap_external>:630: size=10.5 MiB,
> count=105832, average=104 B
> >> /home/robin/devel/reportlab/reportlab/lib/abag.py:19: size=7161 KiB,
> count=27126, average=270 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paraparser.py:3141:
> size=3364 KiB, count=5980, average=576 B
> >>
> /home/robin/devel/reportlab/.py310/lib/python3.10/site-packages/pyphen/__init__.py:160:
> size=2905 KiB, count=41797, average=71 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:776:
> size=1386 KiB, count=32208, average=44 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:92:
> size=1384 KiB, count=26248, average=54 B
> >> /home/robin/devel/reportlab/.py310/lib/python3.10/copy.py:280:
> size=1232 KiB, count=8827, average=143 B
> >> /home/robin/devel/reportlab/reportlab/platypus/frames.py:155: size=1101
> KiB, count=1173, average=962 B
> >> <frozen importlib._bootstrap>:241: size=915 KiB, count=8146,
> average=115 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:773:
> size=881 KiB, count=16104, average=56 B
> >> sys:1: ResourceWarning: unclosed file <_io.BufferedReader
> name='../images/replogo.gif'>
> >> sys:1: ResourceWarning: unclosed file <_io.BufferedReader
> name='../images/testimg.gif'>
> >> Debug memory block at address p=0x5617c33effe0: API ''
> >>    0 bytes originally requested
> >>    The 7 pad bytes at p-7 are not all FORBIDDENBYTE (0xfd):
> >>        at p-7: 0x00 *** OUCH
> >>        at p-6: 0x00 *** OUCH
> >>        at p-5: 0x00 *** OUCH
> >>        at p-4: 0x00 *** OUCH
> >>        at p-3: 0x00 *** OUCH
> >>        at p-2: 0x00 *** OUCH
> >>        at p-1: 0x00 *** OUCH
> >>    Because memory is corrupted at the start, the count of bytes
> requested
> >>       may be bogus, and checking the trailing pad bytes may segfault.
> >>    The 8 pad bytes at tail=0x5617c33effe0 are not all FORBIDDENBYTE
> (0xfd):
> >>        at tail+0: 0x00 *** OUCH
> >>        at tail+1: 0x00 *** OUCH
> >>        at tail+2: 0x00 *** OUCH
> >>        at tail+3: 0x00 *** OUCH
> >>        at tail+4: 0x00 *** OUCH
> >>        at tail+5: 0x00 *** OUCH
> >>        at tail+6: 0x00 *** OUCH
> >>        at tail+7: 0x00 *** OUCH
> >> Enable tracemalloc to get the memory block allocation traceback
> >> Fatal Python error: _PyMem_DebugRawFree: bad ID: Allocated using API
> '', verified using API 'o'
> >> Python runtime state: finalizing (tstate=0x5617c53c8b30)
> >> Current thread 0x00007fd5742b3740 (most recent call first):
> >> <no Python frame>
> >> Aborted (core dumped)
> >
> >
> > for comparison here is the 3.9.1 output> $ python -Xdev -Xtracemalloc
> genuserguide.py
> >>
> /home/robin/devel/reportlab/.py39/lib/python3.9/distutils/__init__.py:1:
> DeprecationWarning: the imp module is deprecated in favour of importlib;
> see the module's documentation for alternative uses
> >>  import imp
> >>
> /home/robin/devel/reportlab/.py39/lib/python3.9/site-packages/fontTools/misc/py23.py:11:
> DeprecationWarning: The py23 module has been deprecated and will be removed
> in the next release. Please update your code.
> >>  warnings.warn(
> >> Built story contains 1843 flowables...
> >> Saved
> "/home/robin/devel/reportlab/REPOS/reportlab/docs/reportlab-userguide.pdf"
> >> [ Top 10 ]
> >> <frozen importlib._bootstrap_external>:587: size=12.4 MiB,
> count=128010, average=102 B
> >> /home/robin/devel/reportlab/reportlab/lib/abag.py:19: size=7132 KiB,
> count=26951, average=271 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paraparser.py:3141:
> size=3364 KiB, count=5980, average=576 B
> >>
> /home/robin/devel/reportlab/.py39/lib/python3.9/site-packages/pyphen/__init__.py:160:
> size=2905 KiB, count=41797, average=71 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:776:
> size=1386 KiB, count=32208, average=44 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:92:
> size=1384 KiB, count=26248, average=54 B
> >> /home/robin/devel/reportlab/.py39/lib/python3.9/copy.py:279: size=1230
> KiB, count=8827, average=143 B
> >> /home/robin/devel/reportlab/reportlab/platypus/frames.py:155: size=1039
> KiB, count=957, average=1112 B
> >> <frozen importlib._bootstrap>:228: size=959 KiB, count=8503,
> average=116 B
> >> /home/robin/devel/reportlab/reportlab/platypus/paragraph.py:773:
> size=881 KiB, count=16104, average=56 B
> >> sys:1: ResourceWarning: unclosed file <_io.BufferedReader
> name='../images/replogo.gif'>
> >> sys:1: ResourceWarning: unclosed file <_io.BufferedReader
> name='../images/testimg.gif'>
> >
> >
> > --
> > https://mail.python.org/mailman/listinfo/python-list
> >
>
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