I observed that zbar was not using qemu during g-ir-scanner and looked
into it. It turns out that I was patching it to export
_PYTHON_SYSCONFIGDATA_NAME as it would build a Python extension module.
That variable leaked into the part of the build where it runs
g-ir-scanner. It ended up calling the cross wrapper. Unfortunately,
there is a short cut "if sysconfig.get_config_var('MULTIARCH') ==
DEB_HOST_MULTIARCH". The left hand gets influenced by setting
_PYTHON_SYSCONFIGDATA_NAME and therefore the short cut is taken
disabling qemu.

Can we change this short cut to avoid this trap? Any suggestions for
how?

Thanks for considering

Helmut

And what was the result? Failing to run the scanner because it was a
host-architecture executable and you don't have transparent qemu
emulation of the host architecture on the build architecture?

I was hoping that sysconfig.get_config_var('MULTIARCH') would return the
hard-coded architecture of the running Python interpreter, which would
have meant that this shortcut was correct. But if your override for
cross-building makes sysconfig describe the host architecture rather
than the build architecture, then yes this is wrong.

Is there anything - perhaps in sys or platform rather than sysconfig -
that would tell us, specifically, the architecture of the running Python
interpreter? Unfortunately I don't see anything immediately useful in
the documentation of those modules.

The sysconfig API documentation says "The sysconfig module provides
access to Python’s configuration information like the list of
installation paths and the configuration variables relevant for the
current platform" which unfortunately doesn't really help us to decide
whether it refers to the host or build platform: either one of those
could reasonably be described as "current".

I think g-ir-scanner is probably slow enough that an exec of the CAN_RUN
helper before we run the actual scanner is not a significant slowdown,
so I think dropping this shortcut would probably be OK. Please could you
propose a tested merge request or patch?

Are you targeting this for a trixie freeze exception, or for forky?

     smcv

Hi Simon,

thanks for your quick followup.

You correctly completed what I left implicit.

The sysconfig module is extensively used while cross building Python
extension modules. Therefore, it describes the host architecture in
common build scenarios indeed.

I concur. In an interpreter with _PYTHON_SYSCONFIGDATA_NAME set, both
sys and platform describe the build architecture, but the interfaces
they provide are not exactly useful in telling the build architecture.

The Python interpreter startup we incur via cross-g-ir-tool should be
larger than CAN_RUN already. I concur that dropping the short-cut should
fix the issue at hand. I've copied d-cross@l.d.o to acquire some more
ideas before moving forward with that approach.

The proposed change bears a bit of risk as it may influence native
builds. It also affects a small minority of packages. I suggest
deferring this to forky.

Helmut

Hello,

Bug #1105149 in gobject-introspection reported by you has been fixed in the
Git repository and is awaiting an upload. You can see the commit
message below and you can check the diff of the fix at:

https://salsa.debian.org/gnome-team/gobject-introspection/-/commit/cedb1da00b5962077d377e704b5db2eafd27e33a
------------------------------------------------------------------------
d/cross-g-ir-tool.in: Don't rely on sysconfig

During cross-compilation of some packages it is necessary to set
the environment variable _PYTHON_SYSCONFIGDATA_NAME, which alters
sysconfig to describe the host rather than build architecture,
meaning that it no longer has facts about the current interpreter.

Closes: #1105149
------------------------------------------------------------------------

(this message was generated automatically)
-- 
Greetings

https://bugs.debian.org/1105149

Now that forky development has started, I've queued up that change.

I checked the equivalent cross wrappers in src:glib2.0, but they are so
much simpler that they already did not have an equivalent bug.

     smcv

We believe that the bug you reported is fixed in the latest version of
gobject-introspection, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1105149@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Jeremy Bícha <jbicha@ubuntu.com> (supplier of updated gobject-introspection package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Sat, 13 Sep 2025 08:39:09 -0400
Source: gobject-introspection
Built-For-Profiles: noudeb
Architecture: source
Version: 1.86.0-1
Distribution: experimental
Urgency: medium
Maintainer: Debian GNOME Maintainers <pkg-gnome-maintainers@lists.alioth.debian.org>
Changed-By: Jeremy Bícha <jbicha@ubuntu.com>
Closes: 1105149
Changes:
 gobject-introspection (1.86.0-1) experimental; urgency=medium
 .
   [ Jeremy Bícha ]
   * New upstream release
 .
   [ Simon McVittie ]
   * d/cross-g-ir-tool.in: Don't rely on sysconfig.
     During cross-compilation of some packages it is necessary to set
     the environment variable _PYTHON_SYSCONFIGDATA_NAME, which alters
     sysconfig to describe the host rather than build architecture,
     meaning that it no longer has facts about the current interpreter.
     (Closes: #1105149)
   * Improve documentation in README.Debian:
     - Simplify recommended gobject-introspection dependency to 1.80.
       The previous recommendation was new in Debian 13 and Ubuntu 24.04,
       but 1.80 is available in both of those releases too, so we can
       recommend something shorter and easier to remember without losing
       portability.
     - Suggest a less intrusive workaround for #1060838/#1111001
     - #1060907 in haskell-haskell-gi was fixed
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We believe that the bug you reported is fixed in the latest version of
gobject-introspection, which is due to be installed in the Debian FTP archive.

A summary of the changes between this version and the previous one is
attached.

Thank you for reporting the bug, which will now be closed.  If you
have further comments please address them to 1105149@bugs.debian.org,
and the maintainer will reopen the bug report if appropriate.

Debian distribution maintenance software
pp.
Jeremy Bícha <jbicha@ubuntu.com> (supplier of updated gobject-introspection package)

(This message was generated automatically at their request; if you
believe that there is a problem with it please contact the archive
administrators by mailing ftpmaster@ftp-master.debian.org)
Format: 1.8
Date: Thu, 18 Sep 2025 14:55:11 -0400
Source: gobject-introspection
Built-For-Profiles: noudeb
Architecture: source
Version: 1.86.0-2
Distribution: unstable
Urgency: medium
Maintainer: Debian GNOME Maintainers <pkg-gnome-maintainers@lists.alioth.debian.org>
Changed-By: Jeremy Bícha <jbicha@ubuntu.com>
Closes: 1105149
Changes:
 gobject-introspection (1.86.0-2) unstable; urgency=medium
 .
   * Release to unstable
 .
 gobject-introspection (1.86.0-1) experimental; urgency=medium
 .
   [ Jeremy Bícha ]
   * New upstream release
 .
   [ Simon McVittie ]
   * d/cross-g-ir-tool.in: Don't rely on sysconfig.
     During cross-compilation of some packages it is necessary to set
     the environment variable _PYTHON_SYSCONFIGDATA_NAME, which alters
     sysconfig to describe the host rather than build architecture,
     meaning that it no longer has facts about the current interpreter.
     (Closes: #1105149)
   * Improve documentation in README.Debian:
     - Simplify recommended gobject-introspection dependency to 1.80.
       The previous recommendation was new in Debian 13 and Ubuntu 24.04,
       but 1.80 is available in both of those releases too, so we can
       recommend something shorter and easier to remember without losing
       portability.
     - Suggest a less intrusive workaround for #1060838/#1111001
     - #1060907 in haskell-haskell-gi was fixed
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