STR9 library in C++

I want to use the RV c++ compiler in combination with the ST91 library.
I renamed all files in this library to *.cpp and rebuild the library.
There is one problem left. Some assembler source files use external symbols.
My question :

How can I access UndefinedHandler that is decleared in a c++ file ?
I tried with __UndefinedHandler with no success....

        AREA Undef, CODE, READONLY
        ARM

        PRESERVE8
        ALIGN

        IMPORT UndefinedHandler
        EXPORT  UndefHandler

UndefHandler

        STMFD   SP!, {R0-R12, LR}       ; Save Workspace & LR to Stack
        MRS     R0, SPSR                ; Copy SPSR to R0
        STMFD   SP!, {R0, R1}           ; Save SPSR to Stack (8-byte)
        BL      Undefined_Handler       ; Branch to Undefined Handler
        LDMFD   SP!, {R0, R1}           ; Restore SPSR to R0
        MSR     SPSR_cxsf, R0           ; Restore SPSR
        LDMFD   SP!, {R0-R12, PC}^      ; Return to program after
                                        ; Undefined Instruction

        END

Thank you.