4.7.3 Passing Parameters by Reference

If the parameter is passed by reference (e.g., Pascal VAR parameters), then the symbol descriptor is v if it is in the argument list, or a if it in a register. Other than the fact that these contain the address of the parameter rather than the parameter itself, they are identical to p and R, respectively. I believe a is an AIX invention; v is supported by all stabs-using systems as far as I know.