5.1.1 Bss Directive

The .bss directive indicates that the output of the assembly code following should be placed at the end of the .bss (uninitialized data) section.

The .bss section is used for local common variable storage. You may allocate address space in the .bss section, but you may not dictate data to load into it before your program executes. When your program starts running, the entire .bss section is filled with zeroes.

Use the .bss directive to switch into the .bss section and then define symbols as usual. You may assemble only zero values into the section. Typically the section will contain only symbol definitions and either .skip or .space directives

# The following symbols (B1 and B2) will be placed in
# the uninitialized data section.
.bss
B1:   .space 4   # 4 bytes reserved for B1
B2:   .space 1   # 1 byte reserved for B2