Calibro: Compilation-Assisted Linking-Time Binary Code Outlining for Code Size Reduction in Android Applications

Recent Android systems have employed pre-compilation technology to boost app launch speed and runtime performance. However, this generates large OAT files that over-consume scarce memory and storage resources in mobile devices. This paper conducts an evaluation of code redundancy in popular production android applications and observes that the code redundancy is up to 25%. To reduce the code size via redundancy elimination, this paper proposes Calibro, a compilation-assisted linking-time binary code outlining method. Calibro consists of two parts, the Compilation-Time code Outlining (CTO) and the Linking-Time Binary code Outlining (LTBO) with information collected at compilation- time. Additionally, a paralleled suffix tree method is proposed to reduce the building time overhead, and a hot function filtering method is proposed to effectively mitigate run-time performance degradation caused by code outlining. Experimental results show that compared to the baseline (the original AOSP version with all available code size optimization enabled), the proposed approach reduces code size in Android applications by more than 15.19% on average, with negligible runtime performance degradation and tolerable building time overhead. Hence the proposed code outlining approach is promising for production deployment.