5.3.1 .bss symbol, length [, algn]

Reserve length (an absolute expression) bytes for a local symbol. The addresses are allocated in the bss section, so that at run-time the bytes start off zeroed. symbol is declared local so it is not visible to other objects. If algn is specified, it is the address alignment required for symbol. The bss location counter is advanced until it is a multiple of the requested alignment. The requested alignment must be a power of 2.