Where they are required, the compiler normally produces RO, RW, and ZI sections from a single source file. These sections contain all the code and data from the source file.

Typically, you create a scatter file that defines an execution region at the required address with a section description that selects only one section.

To place a function or variable at a specific address, it must be placed in its own section. There are several ways to do this:

• Place the function or data item in its own source file.

• Use __attribute__((section("name"))) to place functions and variables in a specially named section, .ARM.__at_address, where address is the address to place the function or variable. For example, __attribute__((section(".ARM.__at_0x4000"))).

  To place ZI data at a specific address, use the variable attribute __attribute__((section("name"))) with the special name .bss.ARM.__at_address

  These specially named sections are called __at sections.

• Use the .section directive from assembly language. In assembly code, the smallest locatable unit is a .section.

• Use the -ffunction-sections compiler option to generate one ELF section for each function in the source file.

  This option results in a small increase in code size for some functions because it reduces the potential for sharing addresses, data, and string literals between functions. However, this can help to reduce the final image size overall by enabling the linker to remove unused functions when you specify armlink --remove.