Protected shared libraries - A new approach to modularity and sharing

Protected Shared Libraries, or PSLs, are a new type of support for modularity that form a basis for building flexible library-based operating system services. PSLs extend the familiar notion of shared libraries with protected state and data sharing across protection boundaries. Protected state information allows PSLs to be used to implement sensitive operating system services. Sharing of data across protection boundaries yields significant performance benefits. These features make PSLs a viable basis on which a complete operating system can be built largely as a set of dynamically loadable libraries without compromising protection or sacrificing performance. PSLs also allow highly flexible implementations of new functionality to be added to current commercial operating systems. A prototype PSL implementation has been built into AIX 3.2.5 and early performance results are encouraging.