These sections hold your program. as and ld treat them as separate but equal sections. Anything you can say of one section is true of another. When the program is running, however, it is customary for the text section to be unalterable. The text section is often shared among processes: it contains instructions, constants and the like. The data section of a running program is usually alterable: for example, C variables would be stored in the data section.

This section contains zeroed bytes when your program begins running. It is used to hold uninitialized variables or common storage. The length of each partial programs bss section is important, but because it starts out containing zeroed bytes there is no need to store explicit zero bytes in the object file. The bss section was invented to eliminate those explicit zeros from object files.

Address 0 of this section is always relocated to runtime address 0. This is useful if you want to refer to an address that ld must not change when relocating. In this sense we speak of absolute addresses being unrelocatable: they do not change during relocation.