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(nasm.info)Section 6.5.1

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6.5.1. `elf' Extensions to the `SECTION' Directive
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   Like the `obj' format, `elf' allows you to specify additional
information on the `SECTION' directive line, to control the type and
properties of sections you declare. Section types and properties are
generated automatically by NASM for the standard section names `.text',
`.data' and `.bss', but may still be overridden by these qualifiers.

   The available qualifiers are:

   * `alloc' defines the section to be one which is loaded into memory
     when the program is run. `noalloc' defines it to be one which is
     not, such as an informational or comment section.

   * `exec' defines the section to be one which should have execute
     permission when the program is run. `noexec' defines it as one
     which should not.

   * `write' defines the section to be one which should be writable when
     the program is run. `nowrite' defines it as one which should not.

   * `progbits' defines the section to be one with explicit contents
     stored in the object file: an ordinary code or data section, for
     example, `nobits' defines the section to be one with no explicit
     contents given, such as a BSS section.

   * `align=', used with a trailing number as in `obj', gives the
     alignment requirements of the section.

   The defaults assumed by NASM if you do not specify the above
qualifiers are:

     section .text    progbits  alloc  exec    nowrite  align=16
     section .rodata  progbits  alloc  noexec  nowrite  align=4
     section .data    progbits  alloc  noexec  write    align=4
     section .bss     nobits    alloc  noexec  write    align=4
     section other    progbits  alloc  noexec  nowrite  align=1

   (Any section name other than `.text', `.rodata', `.data' and `.bss'
is treated by default like `other' in the above code.)