Actually, elf file is a debug file, it contains source and debug information. You only need to use a special software to read it.
Now there are a lot of softwares could do this in the net. I recommend one to you which I think is very easy and convenience, it is
CoDebugger.
CoDebugger is not only able to read the source information from the elf file, but also a debugger...
About how to use CoDebugger, you can see from its website.
