gas

Frequently used directives

• .byte, .2byte, .4byte, .8byte to define a N byte value

  .byte 0xaa
  .2byte 0xaabb
  .2byte 0xaa, 0xbb
  .4byte 0xaabbccdd
  .8byte 0xaabbccdd11223344
  

• .ascii to define an ascii string

  .ascii "foo"   ; allocates 3 bytes
  

• .asciz to define an ascii string with '\0' terminator

  .asciz "foo"   ; allocates 4 bytes (str + \0)
  

• .macro to define assembler macros. Arguments are accessed with the \arg syntax.

  .macro defstr name str
  \name:
      .ascii "\str"
  \name\()_len:
      .8byte . - \name
  .endm
  
  ; use as
  defstr foo, "foobar"
  

  Use \() to concatenate macro argument and literal.

• GNU Assembler

• GNU Assembler Directives

• GNU Assembler x86_64 dependent features