The SECTIONS command controls exactly where input sections are
placed into output sections, their order in the output file, and to
which output sections they are allocated.
You may use at most one SECTIONS command in a script file,
but you can have as many statements within it as you wish. Statements
within the SECTIONS command can do one of three things:
You can also use the first two operations--defining the entry point and
defining symbols--outside the SECTIONS command: see section The Entry Point, and see section Assignment: Defining Symbols. They are permitted here as well for
your convenience in reading the script, so that symbols and the entry
point can be defined at meaningful points in your output-file layout.
If you do not use a SECTIONS command, the linker places each input
section into an identically named output section in the order that the
sections are first encountered in the input files. If all input sections
are present in the first file, for example, the order of sections in the
output file will match the order in the first input file.