What is ".bss"

In computer programming, the name .bss or bss is used by many compilers and linkers for a part of the data segment containing statically-allocated variables represented solely by zero-valued bits initially (i.e., when execution begins). It is often referred to as the "bss section" or "bss segment".

Typically only the length of the bss section, but no data, is stored in the object file. The program loader allocates and initializes memory for the bss section when it loads the program. Operating systems may use a technique called zero-fill-on-demand to efficiently implement the bss segment . In embedded software, the bss segment is mapped into memory that is initialized to zero by the C run-time system before [[Main function (programming)#C and C++|main ]] is entered.

On some computer architectures the application binary interface also supports an sbss segment for "small data". Typically, these data items can be accessed using shorter instructions that may only be able to access a certain range of addresses.