Compacting ARM binaries with the Diablo framework

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Compacting ARM binaries with the Diablo framework

• Dominique ChanetLudo Van Put

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Introduction

• Embedded systems emphasis on compact programs
• How?
• assembly language programming
• compilers optimizing for code size
• specially tweaked libraries
• smart linkers

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ARM

• Widely used in embedded systems
• StrongArm, XScale (PDAs)
• OMAP (cell phones)
• in 2001 76 of all RISC processors shipped were
  based on the ARM instruction set
• Low power consumption
• Special attention for compact code
• Thumb instruction set
• ISA features like conditional execution of all
  instructions, pipeline with integrated barrel
  shifter, ...

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Diablo

• Binary rewriting framework useful for
  compaction, instrumentation, obfuscation,
• Retargetable ports for ARM, MIPS, x86, Alpha,
• At link time
• Inputs object files, libraries
• Output a statically linked executable

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Impact of libraries
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Major compaction opportunities

• initial unreachable code removal
• results of interprocedural constant propagation
• at link time addresses are propagated
• optimize address calculations
• disambiguate indirect jumps
• combined with dead code elimination discard
  parts of functions that can never be executed
• results of interprocedural liveness analysis
• unused function results, ...

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Results
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Conclusions Future Work

• on average 8-11 compaction of the code section
  (depending on platform)
• mostly thanks to unreachable code removal and
  interprocedural constant propagation
• Future work
• more advanced techniques (e.g. factorization,
  stack analysis, ...)
• support for Thumb instruction set