Modern software is bloated, especially for libraries. The unnecessary code not only brings severe vulnerabilities, but also assists attackers to construct exploits. To mitigate the damage of bloated libraries, researchers have proposed several debloating techniques to remove or restrict the invocation of unused code in a library. However, existing approaches either statically keep code for all expected inputs, which leave unused code for each concrete input, or rely on runtime context to dynamically determine the necessary code, which could be manipulated by attackers.

In this paper, we propose Picup, a practical approach that dynamically customizes libraries for each input. Based on the observation that the behavior of a program mainly depends on the given input, we design Picup to predict the necessary library functions immediately after we get the input, which erases the unused code before attackers can affect the decision-making data. To achieve an effective prediction, we adopt a convolutional neural network (CNN) with attention mechanism to extract key bytes from the input and map them to library functions. We evaluate Picup on real-world benchmarks and popular applications. The results show that we can predict the necessary library functions with 97.56% accuracy, and reduce the code size by 87.55% on average with low overheads. These results indicate that Picup is a practical solution for secure and effective library debloating.