An object file is divided into sections containing different types of data.
Some systems have other kinds of sections.
The compiler must tell the assembler when to switch sections. These macros control what commands to output to tell the assembler this. You can also define additional sections. A C expression whose value is a string containing the assembler operation that should precede instructions and read-only data. A C expression whose value is a string containing the assembler operation to identify the following data as writable initialized data.