[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Brett Cannon]

Brett Cannon  added the comment:

Thanks for the PR!

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Brett Cannon]

Change by Brett Cannon :


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status: open -> closed

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[miss-islington]

miss-islington  added the comment:


New changeset 338d54f0a59dc5e5b6c9e7397340169f3a3f8ea4 by Miss Islington (bot) 
(Stefano Rivera) in branch 'master':
bpo-28401: prevent Py_DEBUG builds from trying to import limited ABI modules 
(GH-1766)
https://github.com/python/cpython/commit/338d54f0a59dc5e5b6c9e7397340169f3a3f8ea4


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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Stefano Rivera]

Stefano Rivera added the comment:

> whether this would confuse users since they will simply get an ImportError 
> instead of some other error and thus will they be able to realize why there's 
> a problem?

It's the same behaviour we have for any other module on the import path, that 
doesn't have the right tag. I suppose abi3 is a bit of a special case there, 
because it's expected to be widely supported...

Also, there is a related problem: Because abi3 is in the supported extension 
list, setup.py build will build an abi3 extension (which isn't actually abi3), 
under a pydebug interpreter.

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Brett Cannon]

Brett Cannon added the comment:

So limited ABI modules can't be imported by a Py_DEBUG build. Stefano's patch 
just skips over them. That seems reasonable, but one question I do have is 
whether this would confuse users since they will simply get an ImportError 
instead of some other error and thus will they be able to realize why there's a 
problem?

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components: +Interpreter Core -Library (Lib)
nosy: +brett.cannon, eric.snow, ncoghlan
stage:  -> commit review

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Roundup Robot]

Changes by Roundup Robot :


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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Dmitry Shachnev]

Dmitry Shachnev added the comment:

[Matthias Klose (doko) 2016-10-27 15:45]
> I'm not sure that you really want this, because it would make it impossible 
> to build an extension for the stable ABI for a debug build.

It looks like that is already impossible:

/usr/include/python3.5dm/object.h:65:2: error: #error Py_LIMITED_API is 
incompatible with Py_DEBUG, Py_TRACE_REFS, and Py_REF_DEBUG
 #error Py_LIMITED_API is incompatible with Py_DEBUG, Py_TRACE_REFS, and 
Py_REF_DEBUG
  ^

So in my opinion Stefano's patch makes sense.

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Dmitry Shachnev]

Changes by Dmitry Shachnev :


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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Stefano Rivera]

Stefano Rivera added the comment:

I wouldn't say it's *entirely* Debian-specific. It just bites anyone who 
actually needs these tags to differentiate between built extensions. (Mostly 
Debian)

Yes, changing the tag is a more complete solution. It just seemed that that 
option was decided against, in the relevant PEPs.

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Matthias Klose]

Matthias Klose added the comment:

I'm not sure that you really want this, because it would make it impossible to 
build an extension for the stable ABI for a debug build.  The problem is Debian 
specific, because we install the extension modules for normal and debug builds 
in the same location.  A Debian solution would be to use a different soname for 
stable API debug mode extensions.

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[issue28401] Don't support the PEP384 stable ABI in pydebug builds

[Stefano Rivera]

New submission from Stefano Rivera:

setup.py build for a library using py_limited_api will always generate a stable 
ABI tagged shared library, even under the pydebug interpreter.

This means that extensions that are built for a pydebug interpreter may be 
accidentally (and brokenly) imported in a non-dbg interpreter and vice-versa.

e.g. in python-librtmp, with cffi 1.8.3:
$ python3-dbg setup.py build
...
x86_64-linux-gnu-gcc -pthread -shared -Wl,-O1 -Wl,-Bsymbolic-functions 
-Wl,-z,relro -Wl,-z,relro -g -Og 
-fdebug-prefix-map=/build/python3.5-H9Fri6/python3.5-3.5.2=. 
-fstack-protector-strong -Wformat -Werror=format-security -Wdate-time 
-D_FORTIFY_SOURCE=2 
build/temp.linux-x86_64-3.5-pydebug/build/temp.linux-x86_64-3.5-pydebug/librtmp._librtmp.o
 -lrtmp -o build/lib.linux-x86_64-3.5-pydebug/librtmp/_librtmp.abi3.so

Then:
$ cd build/lib.linux-x86_64-3.5-pydebug
$ python3 -c 'import librtmp'
Traceback (most recent call last):
  File "", line 1, in 
  File 
"/tmp/python-librtmp-0.3.0/build/lib.linux-x86_64-3.5-pydebug/librtmp/__init__.py",
 line 8, in 
from ._librtmp import ffi, lib as librtmp
ImportError: 
/tmp/python-librtmp-0.3.0/build/lib.linux-x86_64-3.5-pydebug/librtmp/_librtmp.abi3.so:
 undefined symbol: _Py_RefTotal

setuptools decides whether to use the stable ABI, by looking at 
imp.get_suffixes(). And obviously, the importer is looking at that too. So, the 
stable ABI tag should simply not be in there.

PEP3149 agrees with this. It has this quote from Martin v. Löwis:
 --with-pydebug would not be supported by the stable ABI because this changes 
the layout of PyObject , which is an exposed structure.

So, here's a patch, to disable support for the stable ABI under pydebug builds.

--
components: Library (Lib)
files: pep384-pydbg.patch
keywords: patch
messages: 278381
nosy: stefanor
priority: normal
severity: normal
status: open
title: Don't support the PEP384 stable ABI in pydebug builds
type: behavior
versions: Python 3.3, Python 3.4, Python 3.5, Python 3.6, Python 3.7
Added file: http://bugs.python.org/file45040/pep384-pydbg.patch

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