Use the compiler intrinsics in inline assembly, for example:

void printReg()
{
    unsigned int spReg, lrReg, pcReg;
    __asm
    {
        MOV spReg, __current_sp()
        MOV pcReg, __current_pc()
        MOV lrReg, __return_address()
    }
    printf("SP = 0x%X\n",spReg);
    printf("PC = 0x%X\n",pcReg);
    printf("LR = 0x%X\n",lrReg);
}

Use embedded assembly to access physical ARM registers from within a C or C++ source file, for example:

__asm void func()
{
    MOV r0, lr
    ...
    BX lr
}

This enables the return address of a function to be captured and displayed, for example, for debugging purposes, to show the call tree.