.size (COFF version)

This directive is generated by compilers to include auxiliary debugging information in the symbol table. It is only permitted inside .def/.endef pairs.

.size is only meaningful when generating COFF format output; when as is generating b.out, it accepts this directive but ignores it.

.size name , expression (ELF version)

This directive is used to set the size associated with a symbol name. The size in bytes is computed from expression which can make use of label arithmetic. This directive is typically used to set the size of function symbols.