What does EXIT and Entry do s.UART

On a number of lines the word Entry is used ( for example in HAL_UARTRate ) what does it do ?.
The same applies for EXIT ( just before HAL_UARTRate )
It is important to know because if I use LDR a1, [a1, #:INDEX:UARTBases] after it it will crash RISC-OS

Entry and EXIT are calls to the Macros in the DDE build environment

In this case, Entry is defined here and EXIT is defined here.

Entry pushes lr, plus any optionally specified registers, and optionally makes room for local variables. EXIT returns from the procedure started by the last Entry.

Thanks now I know what it is doing