How to get source code for NvInfer?

Hi!
How to get source code for NvInfer, hoe can I modify its functions as foreymaple teh excute of the context?

Please see the reply in https://devtalk.nvidia.com/default/topic/1002468/jetson-tx1/can-i-modify-nvinfer-how-can-i-get-the-last-layers-/post/5122130/#5122130