openjpeg @1.4-r697 openjpeg/ffmpeg/libjasper symbol collision

[marin.saric@…]

The purpose of this ticket is to point out a serious issue with OpenJPEG that can lead to unpredictable crashes and seek feedback and advice.

I volunteer to cherry-pick the simple symbol-mangling patch from the OpenJPEG trunk and apply it to the stable version of OpenJPEG currently in MacPorts.

This issue has been discussed and addressed in the OpenJPEG trunk: ​http://code.google.com/p/openjpeg/issues/detail?id=30

Background information: OpenJPEG was designed as an alternative to libjasper, a library providing the JPEG2000 format functionality. Ideally, a project will use either OpenJPEG or libjasper. Some private symbols in OpenJPEG (such as jp2_decode), which are never called by the library user's code end up colliding with the public library API symbols of libjasper.

ffmpeg is a popular library that is compiled with OpenJPEG support in MacPorts.

A program (or, even worse, a dylib plugin) relying on libjasper can also depend on ffmpeg. Even worse, a program loading a dylib plugin can have OpenJPEG already loaded, tripping up a segmentation fault once the plugin loads and the code to open a JPEG2000 file executes.

A simple fix is to change the name of the offending private functions in the OpenJPEG code and recompile openjpeg.

[jmroot (Joshua Root)]

Out of curiosity, why isn't this issue avoided with a two-level namespace? Or does some of this stuff force a flat namespace?

[marin.saric@…]

I stumbled upon this problem during static linking and didn't even think of Apple's clever two-level namespace scheme. Considering Qt4 binaries are still built with -flat_namespace, I am guessing the problem can resurface..

Also there's no two-level namespace equivalent during static linking.

For example, when trying to link opencv statically you run into this: opencv links against jasper and ffmpeg, ffmpeg links against openjpeg and boom you have duplicate symbols.

However, the symbol collision is an accident. A private function got exported under a common name..

[jmroot (Joshua Root)]

Fixed in 1.5.