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regression: PySys_SetArgvEx(0, NULL, 0): SystemError: Python-3.8.0b3/Objects/unicodeobject.c:2089: bad argument to internal function #82107

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hroncok mannequin opened this issue Aug 23, 2019 · 6 comments
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regression: PySys_SetArgvEx(0, NULL, 0): SystemError: Python-3.8.0b3/Objects/unicodeobject.c:2089: bad argument to internal function #82107

hroncok mannequin opened this issue Aug 23, 2019 · 6 comments
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3.8 only security fixes 3.9 only security fixes extension-modules C modules in the Modules dir

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@hroncok
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hroncok mannequin commented Aug 23, 2019

BPO 37926
Nosy @vstinner, @hroncok
PRs
  • bpo-37926: Fix PySys_SetArgvEx(0, NULL, 0) #15415
  • [3.8] bpo-37926: Fix PySys_SetArgvEx(0, NULL, 0) crash (GH-15415) #15420
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    Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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    GitHub fields:

    assignee = None
closed_at = <Date 2019-08-23.11:23:48.102>
created_at = <Date 2019-08-23.07:39:09.430>
labels = ['extension-modules', '3.8', '3.9']
title = 'regression: PySys_SetArgvEx(0, NULL, 0): SystemError: Python-3.8.0b3/Objects/unicodeobject.c:2089: bad argument to internal function'
updated_at = <Date 2019-09-05.14:43:15.499>
user = 'https://github.com/hroncok'

    bugs.python.org fields:

    activity = <Date 2019-09-05.14:43:15.499>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-08-23.11:23:48.102>
closer = 'vstinner'
components = ['Extension Modules']
creation = <Date 2019-08-23.07:39:09.430>
creator = 'hroncok'
dependencies = []
files = []
hgrepos = []
issue_num = 37926
keywords = ['patch']
message_count = 6.0
messages = ['350262', '350268', '350269', '350275', '350276', '351201']
nosy_count = 2.0
nosy_names = ['vstinner', 'hroncok']
pr_nums = ['15415', '15420']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue37926'
versions = ['Python 3.8', 'Python 3.9']
    @hroncok
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    hroncok mannequin commented Aug 23, 2019

    There is a regression between Python 3.7 and 3.8 when using PySys_SetArgvEx(0, NULL, 0).

    Consider this example:

    #include <Python.h>

int main() {
    Py_Initialize();
    PySys_SetArgvEx(0, NULL, 0);  /* HERE */
    PyRun_SimpleString("from time import time,ctime\n"
                       "print('Today is', ctime(time()))\n");
    Py_FinalizeEx();
    return 0;
}

    This works in 3.7 but no longer does in 3.8:

    $ gcc $(python3.7-config --cflags --ldflags) example.c 
$ ./a.out 
Today is Fri Aug 23 07:59:52 2019

$ gcc $(python3.8-config --cflags --ldflags --embed) example.c 
$ ./a.out 
Fatal Python error: no mem for sys.argv
SystemError: /builddir/build/BUILD/Python-3.8.0b3/Objects/unicodeobject.c:2089: bad argument to internal function

    Current thread 0x00007f12c78b9740 (most recent call first):
    Aborted (core dumped)

    The documentation https://docs.python.org/3/c-api/init.html#c.PySys_SetArgvEx explicitly mentions passing 0 to PySys_SetArgvEx:

    "if argc is 0..."

    So I guess this is not something you shouldn't do.

    @hroncok hroncok mannequin added 3.8 only security fixes extension-modules C modules in the Modules dir labels Aug 23, 2019
    @vstinner
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    Oops, it's my fault! PR 15415 fix the crash.

    The regression was introduced by:

    commit 74f6568
    Author: Victor Stinner <vstinner@redhat.com>
    Date: Fri Mar 15 15:08:05 2019 +0100

    bpo-36301: Add _PyWstrList structure (GH-12343)

    Simplified change:

    •    static wchar_t \*empty_argv[1] = {L""};

    + wchar_t* empty_argv[1] = {L""};

    It's a deliberate change to not waste memory: PySys_SetArgvEx() (make_sys_argv()) is only called once, whereas static keeps the memory for the whole lifecycle of the process.

    But I didn't notice a subtle issue with memory allocated on the stack: the code works well with gcc -O0! The bug only triggers with gcc -O3.

    @vstinner
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    New changeset c486825 by Victor Stinner in branch 'master':
    bpo-37926: Fix PySys_SetArgvEx(0, NULL, 0) crash (GH-15415)
    c486825

    @vstinner
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    New changeset ca9ae94 by Victor Stinner in branch '3.8':
    bpo-37926: Fix PySys_SetArgvEx(0, NULL, 0) crash (GH-15415) (GH-15420)
    ca9ae94

    @vstinner
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    I tested my fix manually using example from msg350262 and gcc -O3 (./configure && make): I can reproduce the crash without the change, and I confirm that my change fix the crash.

    Thanks Miro for the bug report: the fix will be included in next Python 3.8 beta release. I fixed the bug in 3.8 and master branches (3.7 is not affected).

    @vstinner vstinner added the 3.9 only security fixes label Aug 23, 2019
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    vstinner commented Sep 5, 2019

    FYI this bug was found in paraview in Fedora Rawhide: https://bugzilla.redhat.com/show_bug.cgi?id=1743896

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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