Kernel module binary compatibility with debug features


 * Summary: Kernel module binary compatibility with debug features
 * Proposer: Tim Bird, Sony Mobile
 * Status: Not selected in 2013 to be sponsored by the CE Workgroup

Description
Sometimes, the workflow for embedded systems include obtaining kernel modules from 3rd party vendors or other software teams. In certain situations, it can be difficult to re-compile and re-install these 3rd party modules, even though the kernel on a system can be re-configured, rebuilt and re-installed.

This feature proposes to isolate the kernel module interface from changes in certain kernel debug features, so that turning on those feature will not create binary incompatibility with a newly configured and deployed kernel.

For example, if a kernel is compiled with CONFIG_DEBUG_SPINLOCK, then modules which use spinlocks may not be able to be supported without being re-compiled with the same debug option. It is believed that this same restriction applies to the following kernel debug features:
 * ftrace
 * perf
 * kprobe
 * SLUB_DEBUG
 * DEBUG_SPINLOCK

It would be nice to be able to enable and disable debug features in the kernel without changing the kernel's module binary compatibility.

This would involve somehow insulating the kernel from problems when it was configured with a particular debug feature, but a module does not support that configuration. This is mainly targetted at things like structure extensions in the debug case, and having the kernel core detect multiple structure formats at runtime, and deal with them correctly. It might also involve making sure that function calls which bypassed the debug infrastructure (such as a spinlock debug wrappers or a trace wrappers) by the original compiled module continued to work correctly.

Related work

 * Module symbol versioning may be related to this.
 * See section 6 of: https://www.kernel.org/doc/Documentation/kbuild/modules.txt

Scope
Unknown

Contractor Candidates
None Yet.

Reasons for CEWG not selecting this project
There was concern that upstream kernel developers would break any compatibility later that was created, over time. Also, there was concern over who would maintain the support for this. Finally, there were technical issues with how to collapse and expand structures based on debug features.