Firmware is the soul of an embedded system

and disassembly is a necessary step to understand the operational mechanism or detect the vulnerabilities of the firmware.When disassembling a firmware

it should first determine the processor type of running environment and the image base of firmware.In general

the processor type can be got by tearing down the device or consulting the product manual.However

at present there is still no automated tool that can be used to obtain the image base of firmware.Since the processors of majority embedded systems are ARM architecture

in this paper we focus on the firmwares in ARM and propose an automated method to determine the base address.Firstly

by studying the storage rule and loading mode of the string we present two algorithms to calculate the string offset and the string address loaded by LDR instruction.Then with these information

we proposed a DBMAS (Determining image Base by Matching Addresses of Strings) algorithm to determine the image base.Experimental results indicate the proposed method can successfully determine the image base of firmware that uses the LDR instruction to load string address.