Reducing calling convention overhead in object-oriented programming on embedded ARM thumb-2 platforms

Abstract

This paper examines the causes and extent of code size overhead caused by the ARM calling convention in Thumb-2 binaries. We show that binaries generated from C++ source files generally have higher amounts of calling convention overhead, and present a binary file optimizer to eliminate some of that overhead. Calling convention overhead can negatively impact power consumption, flash memory costs, and chip size in embedded or otherwise resource-constrained domains. This is particularly true on platforms using "compressed" instruction sets, such as the 16-bit ARM Thumb and Thumb-2 instruction sets, used in virtually all smartphones and in many other smaller-scale embedded devices. In this paper, we examine the extent of calling convention overhead in practical software, and compare the results of C and C++ programs, and find that C++ programs generally have a higher percentage of calling-convention overhead. Finally, we demonstrate a tool capable of eliminating some of this overhead, particularly in the case of C++ programs, by modifying the calling conventions on a per-procedure basis.