1. CSE 60641: Operating Systems
Tuesday, July 09, 2019
CSE 60641: Operating Systems
Extensibility safety and performance in the SPIN operating system Bershad, B. N., Savage, S., Pardyak, P., Sirer, E. G., Fiuczynski, M. E., Becker, D., Chambers, C., and Eggers, S. SOSP '95
This paper was published in the same SOSP as Exokernel
9-Jul-19
CSE 60641: Operating Systems

2. CSE 60641: Operating Systems
Goals
Extensibility: Applications can dynamically extend system to provide specialized services
Safety: Kernel is protected from actions of extensions
Performance: Extensibility and safety have low cost
Approach:
Put extension code in the kernel: Cheap communication
Use language protection features: Static safety
Dynamically interpose on any service: Fine-grained extensibility
7/9/2019
CSE 60641: Operating Systems

3. CSE 60641: Operating Systems
7/9/2019
CSE 60641: Operating Systems

4. CSE 60641: Operating Systems
Comparable system
Modules/DLLs in OS
Modules are per system and not per application
Modules offer no protection – blue screen of death if things go wrong inside a module
Exokernel
Some protection boundary crossing, optimized in Aegis and might not be general purpose
SPIN relies on Modula3 for performance and static analysis of code
7/9/2019
CSE 60641: Operating Systems

5. CSE 60641: Operating Systems
Safety: Modula3, dynamically restricts access to private interfaces at linktime
Extensibility: Event based model, replace event handler
SPIN implements events that cannot be safely extended
Notion of trust, Modula gives you safety but not trust
7/9/2019
CSE 60641: Operating Systems

6. CSE 60641: Operating Systems
Discussion
Language based approach
7/9/2019
CSE 60641: Operating Systems