SLINKY: Static Linking Reloaded
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The document discusses 'slinky', a method of static linking which combines program libraries into a single executable, addressing the drawbacks of traditional static and dynamic linking. It enhances efficiency by sharing memory and disk space while reducing network bandwidth through deduplication. The method shows minimal performance degradation, comparable memory footprints, and low overhead compared to dynamic linking.
![Static Linking
• Incorporating libraries at compile-time[^1]
• Pros
• Easy to understand, implement, and use
• Self-contained apps
• Cons
• Duplications - spatial inefficiency
[^1]: More precisely, at link-time](https://image.slidesharecdn.com/slinkystaticlinkingreloaded-131003185721-phpapp02/85/SLINKY-Static-Linking-Reloaded-3-320.jpg)
SLINKY: Static Linking Reloaded
- 1. SLINKY: Static Linking Reloaded Christian Collberg, John Hartman et. al. CSC 630, Fall 2013, University of Arizona Sumin Byeon
- 2. Linking • Combining a program and its libraries into a single executable • Resolving symbolic names of variables and functions into their resulting addresses
- 3. Static Linking • Incorporating libraries at compile-time[^1] • Pros • Easy to understand, implement, and use • Self-contained apps • Cons • Duplications - spatial inefficiency [^1]: More precisely, at link-time
- 4. Dynamic Linking • Deferring linking until run-time • Pros • Space efficient (disk and memory) • Flexibility • Cons • Complexity (e.g., version, path, dependency, etc.) • Potential security risks
- 5. SLINKY • Implicit sharing of libraries and data by deduplication • Best of both worlds • Sharing memory pages • Sharing disk space • Reducing network bandwidth
- 6. Sharing Memory Pages • When a page modified, it is no longer valid for other processes. Potential solution: copy-on- write. • Share read-only code pages • Data pages are likely modified, thus unlikely to be shared anyway • slink, digest, a set of Linux kernel modifications
- 7. Slink • Position independent code required • Converts a dynamically linked executable into a statically linked executable • Finds all necessary libraries, organizes them in the process’s address space, and resolves symbols
- 8. Digest • Inserts the digests for each code page • Linux page: 4 KB, digest: 20 bytes - less than 0.5% overhead
- 9. Kernel Modifications • Per-process digest table (PDT) - Maps page number to digest • Global digest table (GDT) - Contains the digest of every code page in memory
- 10. Security • Possibility of inserting malicious code • Digest verification before loading a page to the GDT • Memory protection hardware • SHA-1 or a different hash function of your choice
- 11. Sharing Disk Space • Breaking an executable into variable-size chunks • Only one copy of each unique chunk is stored • Similar idea to LBFS
- 12. Reducing Network Bandwidth • Transfers only a fraction of the chunks • The initial transfer represents a worst-case scenario • Deduplication!
- 13. Performance • Measured: • Elapsed time to build the Linux kernel • Page fault handling in both an unmodified Linux kernel and a modified kernel • Number of page faults - SLINKY’s effect on the page fault rate and the memory footprints • Suffers fewer page faults than their dynamically linked counterparts • Page fault rate decreased after several other executables have added pages to the GDT
- 14. Memory Footprint
- 15. Storage Space
- 16. Network Bandwidth • File size: SLINKY exe >>>>> dynamically linked exe • Amount of transferred data: SLINKY exe > dynamically linked exe
- 17. Conclusion • SLINKY overcomes disadvantages of static linking by implicitly sharing data chunks based on their digests • Trivial performance degradation, comparable memory footprint to dynamic linking, and low overhead on storage