Bug 1613614

Summary:	py-bt is broken, results in exception
Product:	[Fedora] Fedora	Reporter:	ell1e <el>
Component:	python3	Assignee:	Charalampos Stratakis <cstratak>
Status:	CLOSED DUPLICATE	QA Contact:	Fedora Extras Quality Assurance <extras-qa>
Severity:	unspecified	Docs Contact:
Priority:	unspecified
Version:	28	CC:	afazekas, bkabrda, cedric.bellegarde, cstratak, dmalcolm, mcyprian, mhroncok, mplch, pviktori, rkuska, shcherbina.iryna, tomspur, torsava, vstinner
Target Milestone:	---
Target Release:	---
Hardware:	Unspecified
OS:	Unspecified
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Fixed In Version:		Doc Type:	If docs needed, set a value
Doc Text:		Story Points:	---
Clone Of:
Clones:	1639242 (view as bug list)		Environment:
Last Closed:	2018-12-04 16:21:21 UTC	Type:	Bug
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:
Bug Blocks:	1639242, 1660220

Description ell1e 2018-08-08 02:10:22 UTC

Description of problem:
py-bt is broken, results in exception:

(gdb) py-bt
Traceback (most recent call first):
  (frame information optimized out)
Python Exception <class 'TypeError'> 'FakeRepr' object is not subscriptable: 
Error occurred in Python command: 'FakeRepr' object is not subscriptable

It worked fine in a recent version before that.

Version-Release number of selected component (if applicable):
python3: python3-3.6.6-1.fc28.src.rpm
gdb: 8.1-25.fc28

How reproducible:
100%

Steps to Reproduce:
1. Open gdb
2. Attach to python3 process
3. Type py-bt

Actual results:
doesn't work, gives error Python Exception <class 'TypeError'> 'FakeRepr' object is not subscriptable

Expected results:
works

Additional info:

Comment 1 Victor Stinner 2018-10-15 10:59:57 UTC

I reproduced the issue:

$ sudo dnf debuginfo-install python3

$ cat x.py
import time
def dodo():
    print("dodo")
    time.sleep(3600)
dodo()

vstinner@apu$ gdb -args python3 x.py
GNU gdb (GDB) Fedora 8.1.1-3.fc28
(...)
Reading symbols from python3...Reading symbols from /usr/lib/debug/usr/bin/python3.6-3.6.6-1.fc28.x86_64.debug...done.
done.
Dwarf Error: could not find partial DIE containing offset 0x316 [in module /usr/lib/debug/usr/bin/python3.6-3.6.6-1.fc28.x86_64.debug]

(gdb) run
Starting program: /usr/bin/python3 x.py
(...)
dodo

^C
Program received signal SIGINT, Interrupt.
0x00007ffff6bf2787 in select () from /lib64/libc.so.6

(gdb) py-bt
Traceback (most recent call first):
  <unknown at remote 0x7ffff7e5f7e0>
Python Exception <class 'TypeError'> 'FakeRepr' object is not subscriptable: 
Error occurred in Python command: 'FakeRepr' object is not subscriptable


The root issue comes from gdb:
"Dwarf Error: could not find partial DIE containing offset 0x316 [in module /usr/lib/debug/usr/bin/python3.6-3.6.6-1.fc28.x86_64.debug]"

I debugged /usr/lib/debug/usr/lib64/libpython3.6m.so.1.0-3.6.6-1.fc28.x86_64.debug-gdb.py : the FakeRepr error indirectly comes from the fact that gdb fails to read debug symbols (the Dwarf Error).


On the Python side, python-gdb.py should be enhanced to better handle such error (exception while computing the line number), but the root issue is in gdb which fails to read debug symbols.

Comment 2 Victor Stinner 2018-10-15 11:27:00 UTC

> On the Python side, python-gdb.py should be enhanced to better handle such error (exception while computing the line number)

I created https://bugs.python.org/issue34989 and proposed a fix for that.

Comment 3 Victor Stinner 2018-10-15 11:31:25 UTC

> the root issue is in gdb which fails to read debug symbols

I created bug #1639242 to track the gdb issue.

Comment 4 Cédric Bellegarde 2018-11-23 21:57:56 UTC

Looks issue if fixed on python side, any chance to get the fix in Fedora 29?

Comment 5 Petr Viktorin (pviktori) 2018-11-26 09:11:06 UTC

The Python change is just to get a better error message.
The issue needs to be fixed in gdb.

Comment 6 Victor Stinner 2018-12-04 16:21:21 UTC

gdb has been fixed in Fedora 28 and 29 and I confirm that it fixed the py-bt command:
https://bugzilla.redhat.com/show_bug.cgi?id=1639242#c10

*** This bug has been marked as a duplicate of bug 1639242 ***