How to Cast a void* ponter to a char without a warning?

I am using the RTX mailbox and a lot of it's usage uses casting of the mailbox message to other types - a really quick and clever way to use it(thanks Keil :). When I cast a void * vPointer to a unigned int - like (uint32_t)vPointer - the compiler is happy - but when I cast to a signed char - like (int8_t)vPointer the compiler complains and says:

Source_App\TerminalDrv.c(56): warning: #767-D: conversion from pointer to smaller integer

Now it all works fine ... but what do I do to stop it complaining?

uint32_t TerminalControllerGetChar(int8_t *pcRxedChar )
{
void * pvmbxTerminalRx;
uint32_t ulNoRxMessage,ulI;

        ulNoRxMessage = SIZEOF_OS_MBX_RXTERMINAL - os_mbx_check(mbxHandleTerminalRx);

        if(ulNoRxMessage == 0)
                return 0 ;
        else
        {
        for(ulI = 0;ulI < ulNoRxMessage ; ulI++)
                {
                if(os_mbx_wait(mbxHandleTerminalRx,(void **)&pvmbxTerminalRx,0x0000) == OS_R_OK)
                        {
                     *pcRxedChar  = (int8_t)pvmbxTerminalRx; 
                        pcRxedChar++;
                        }
                else
                        {
                        break;
                        }
                }
        }
return ulNoRxMessage;
}