llvm dev - Sep 2010 - [LLVMdev] Hidden function (that calls main) ?

Hi

For quiet some time I have noticed a function in my FunctionPasses and
CallGraphSCCPasses that calls main().
I think this is probably what does all the program initialization, but
I was wondering if there is any documentation on how this all works in
the context of LLVM?

I ask because I haven't been able to search successfully for much
documentation, and I don't see the IR code when I disassemble the
bitcode file.
I think it is probably just part of the C runtime, but I don't know
why it is showing up in the passes if it's not in the bitcode.

Thanks

Puyan