基于位运算的固件代码变量区间分析法

变量区间分析是程序代码数据流分析的重要部分。固件反汇编代码存在字节运算和位运算两类运算,当变量取值范围较大时,依次迭代法不能高效地分析经位运算后的结果的取值区间。提出一种快速位运算方法,即根据变量取值区间范围,先将变量转化为不确定位形式再进行位运算;提出一种区间生成算法,即把不确定位形式转化为区间来实现字节运算。实验结果表明,该基于位运算的固件代码变量区间分析方法在程序变量取值范围较大时效率远远高于依次迭代法,而且在各种变量取值区间范围内所需时间稳定,并随着区间范围的增大,其有略微下降趋势。

Variable Intervals Analysis of Firmware Code Based on Binary-bit Operation

The variable intervals analysis plays an important role in program data-flow analysis. There are two different operations, word-level and bit level. For the traditional iterative algorithm is inefficient to analyze the result intervals of bitwise operations if the variable has a large range, a quick bitwise operation method was proposed, which turns variables into the uncertainty bit form, and then makes the bitwise operators. When the uncertainty bit form of a variable needs to do word-level operation, the interval generated algorithm proposed can convert the form to the intervals. The experimental results show that the proposed method is time-consuming stability and more efficient than iterative algorithm with variable range large, and has a downward trend when the variable range expands.