[Bug 727017] New: Strategy for binary compatibility from 1.2 to 1.4

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=727017
  GStreamer | gst-plugins-bad | git

           Summary: Strategy for binary compatibility from 1.2 to 1.4
    Classification: Platform
           Product: GStreamer
           Version: git
        OS/Version: Linux
            Status: UNCONFIRMED
          Severity: critical
          Priority: Normal
         Component: gst-plugins-bad
        AssignedTo: gstreamer-bugs at lists.freedesktop.org
        ReportedBy: gb.devel at gmail.com
         QAContact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---


Should binary compatibility be maintained from 1.2 to 1.4, here are my inputs
and concerns on that matter.

There are readily binary incompatible changes in codecparsers:
http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/commit/gst-libs/gst/codecparsers/gsth264parser.h?id=af78b45979564035ce4f2535d7257201112f776b
http://cgit.freedesktop.org/gstreamer/gst-plugins-bad/commit/gst-libs/gst/codecparsers/gsth264parser.h?id=529ece338fcefd8291e09d6d3fe66357df13078f
(etc.)

I can bear with the changes, since I always include a local copy into
gstreamer-vaapi. But I just wanted to point out the issue in case this affects
others.

The more general problem I see is that, even if new fields are added at the
bottom of a data structure, this yields an incompatible binary change. Imagine
for instance that GstH264SPS is allocated on the stack, new fields get added to
the end, but the app is not rebuilt. So, we end up overwriting stack while
parsing.

In theory, this is not a situation specific to -bad codecparsers, but this can
be of general concern. A change in a data structure is always an ABI change.
The only generic way to circumvent that is to either bump the SONAME of the
library, or add some sort of versioning to the data structures. The latter
approach is totally unconvenient and visually ugly. The former is simple but
needs the user apps to be rebuilt.

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