Abstract

Floating point virtualization enables unmodified application binaries to utilize alternative arithmetic systems such as MPFR without code changes, but its performance overhead is a barrier to adoption. The existing trap-and-emulate model suffers from a significant virtualization bottleneck using general-purpose signal delivery mechanisms which take thousands of cycles. We introduce three techniques to reduce virtualization overhead. Trap short-circuiting bypasses general-purpose signal delivery for an 8x reduction in trap delegation overhead. Instruction sequence emulation amortizes trap costs by emulating multiple instructions per trap, achieving up to 32x reduction in trap frequency. And kernel-bypass for correctness instrumentation eliminates traps and signals for correctness and reduces related overheads substantially. Our implementation within the FPVM system on x64/Linux demonstrates a 10x reduction in per-instruction overhead which, compared to the lower bound performance set by the alternative arithmetic system, drops virtualization overhead from up to 20x to 1.65x. This is for the alternative arithmetic system that is the worst case for virtualization overheads. More expensive systems will fare even better.