Rephrased: How to get function virtual starting address from MCSymbolRefExpr?

I was mistaken as to needing the virtual address of the section , but really need to know the virtual address of the beginning of the function that contains the label whose symbol expression we have.

I have a case where I the expression (MCSymbolRefExpr) is the offset from the beginning of the function.

AsmPrinter::EmitJumpTableEntry() calls [EmitGPRel32Value()](
   case [MachineJumpTableInfo::EK_GPRel32BlockAddress]( {
     // EK_GPRel32BlockAddress - Each entry is an address of block, encoded
     // with a relocation as gp-relative, e.g.:
     //     .gprel32 LBB123
     [MCSymbol]( *MBBSym = MBB->[getSymbol](;
     [OutStreamer]([EmitGPRel32Value]([MCSymbolRefExpr::Create](, [OutContext](;

But can't in the process seem to lose the hook to the parent function. 
It would seem that we need to add [MachineBasicBlock]( *MBB to the call, but
if that isn't necessary would like to know how else to achieve the goal