Bss Section Initialization

But pedantry aside the bss section traditionally is that section that contains all the uninitialized variables which according to spec must be set to all zeros before main begins.

Bss section initialization. Unix like systems and windows initialize the bss section to zero allowing c and c statically allocated variables initialized to values represented with all bits zero to be put in the bss segment. What you see as initialization of bss is what is required by a standard ansi c c startup code. Uninitialized data starts at the end of the data segment and contains all global variables and static variables that are initialized to zero or do not have explicit initialization in source code.

Since local3 is un initialized it is allocated in the bss and since local 4 is explicitly initialized it is allocated in the initialized data segment. In the case of cw with gcc compiler these can be found on arm start c file. As both are local they are indicated by small letters.

The bss segment also known as uninitialized data is usually adjacent to the data segment. For instance a variable declared static int i. If you don t want that or you don t need that you could skip this initialization part in the startup code.

The linker requires each object be defined once with the exception that uninitialized variables tentatively go in the common or bss section and can be multiply defined. Bss this section holds uninitialized data that contribute to the program s memory image. That name comes from the old unix assembler and you won t find a text data and bss in the segment names generated by the keil tools.

The bss segment contains all global variables and static variables that are initialized to zero or do not have explicit initialization in source code. By definition the system initializes the data with zeros when the program begins to run. In this case the memory is set to zeros data.

The section occupies no file space as indicated by the section type sht nobits. Would be contained in the bss segment. For instance a variable defined as static int i.