9.5. ELF Extensions to the COMMON Directive

ELF also allows you to specify alignment requirements on common variables. This is done by putting a number (which must be a power of two) after the name and size of the common variable, separated (as usual) by a colon. For example, an array of doublewords would benefit from 4-byte alignment:

common  dwordarray 128:4

This declares the total size of the array to be 128 bytes, and requires that it be aligned on a 4-byte boundary.