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JIFL: JIT Instrumentation Framework for Linux

JIFL: JIT Instrumentation Framework for Linux. Marek Olszewski Adam Czajkowski Keir Mierle University of Toronto. Instrumenting Operating Systems. Operating systems are growing in complexity Becoming harder to understand

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JIFL: JIT Instrumentation Framework for Linux

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  1. JIFL: JIT Instrumentation Framework for Linux Marek Olszewski Adam Czajkowski Keir Mierle University of Toronto

  2. Instrumenting Operating Systems • Operating systems are growing in complexity • Becoming harder to understand • Kernel instrumentation is a well know method of combating this problem • Used for: debugging, profiling, monitoring, coverage testing, security auditing... • Dynamic instrumentation is especially useful • No recompilation & no reboot • Good for debugging systemic problems • Feasible in production settings

  3. Dynamic Instrumentation • All dynamic instrumentation tools for operating systems are probe based • Overwrite existing code with jump/trap instructions • Efficient on fixed length architectures • Slow on variable length architectures • Must use trap instruction (and hash table lookup) • JIT-based instrumentation can be more efficient • Proven itself for user space (Pin, Valgrind) • Probe-based instrumentation is seldom used in user-space

  4. Probe-based Instrumentation Trap Handler Instrumentation Code OS Code • Look up which instrumentation to call • Call instrumentation • Emulate overwritten instruction Instrumentation Code

  5. JIT Instrumentation • JIT instrumentation rewrites the OS code with calls to instrumentation code • Creates a duplicate instrumented copy of the OS • Called the code-cache • Since instrumentation is dynamic, it is not feasible to rewrite the entire operating system up-front • Instrumentation is performed just-in-time, basic block by basic block, right before each new basic block is executed. • The resulting code is fast • No hash table lookup required • Though there is some cost in executing in the code-cache

  6. JIT Instrumentation Duplicate Copy of OS Instrumentation Code OS Code Instrumentation Code

  7. Software Architecture

  8. Performance Evaluation Apache Web Server Throughput

  9. Conclusions • JIT instrumentation viable for operating systems • Fine grained instrumentation now possible for kernel space on variable length architectures • Intel’s x86 • AMD’s AMD64 • Great performance • Though it comes with a fixed cost

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