Visual C# backtrace: how to know where [external code] resides?

I am using visual c# to debug a large c# project. The project is very large and only some of the pdbs are build by myself. I can build all the pdb however it's very time consuming. I am debugging a backtrace but a part of the trace is marked with [External Code]. I know some pdb is missing, but how can I know which DLL the external code resides? In C I can get the EIP then see the process mapping to determine where the EIP lives, but how this can be done in .Net environment?