From Dynamic Loading to Extensible Transformation: An Infrastructure for Dynamic Library Transformation

The dynamic linker and loader has been one of the fundamental software, and more than 99% of binaries are dynamically linked on Ubuntu. On one hand, vendors are going to break production software into more and more dynamic libraries to lower the maintenance cost. On the other hand, customers require the dynamic loader to provide rich functionalities to serve their isolation, security, and performance demands. However, existing dynamic loaders are implemented in a monolithic fashion, so they are difficult to extend, configure and optimize. This paper presents iFed, an infrastructure for extensible and flexible dynamic library transformation. We design iFed in a pass-based architecture to compose various functional and optimization passes. iFed uses a runnable in-memory format to represent libraries and coordinate among multiple transformation passes. We further implement two optimization passes in iFed, which efficiently leverages hugepages and eliminates relocation overhead. iFed is implemented as a drop-in replacement of the current system default dynamic loader. We evaluate iFed and its optimization passes with a wide range of applications on different hardware platforms. Compared to the default glibc dynamic loader, iFed reduces an order of magnitude of TLB miss. We improve the throughput of a dynamic website by 13.3%, along with a 12.5% reduction of tail latency without any modifications to the applications.