What does code pattern like .size X,.-X do?

Question

My question is about some popular but not well documented code I have found in ARM CORTEX M startup files like this STM32.

The \'pattern\' is:

.size         


        

Answer 1

That is placed at the end of function X, and the size of the function is the difference between the end of the function and the beginning. . is the current location so it's saying .size x is the difference between here and the label x.