GNU Info

(nasm.info)Section 3.9

---

Next: Chapter 4 Prev: Section 3.8 Up: Chapter 3

---

Enter node , (file) or (file)node

3.9. Local Labels
=================

   NASM gives special treatment to symbols beginning with a period. A
label beginning with a single period is treated as a _local_ label,
which means that it is associated with the previous non-local label.
So, for example:

     label1  ; some code
     
     .loop
             ; some more code
     
             jne     .loop
             ret
     
     label2  ; some code
     
     .loop
             ; some more code
     
             jne     .loop
             ret

   In the above code fragment, each `JNE' instruction jumps to the line
immediately before it, because the two definitions of `.loop' are kept
separate by virtue of each being associated with the previous non-local
label.

   This form of local label handling is borrowed from the old Amiga
assembler DevPac; however, NASM goes one step further, in allowing
access to local labels from other parts of the code. This is achieved
by means of _defining_ a local label in terms of the previous non-local
label: the first definition of `.loop' above is really defining a
symbol called `label1.loop', and the second defines a symbol called
`label2.loop'. So, if you really needed to, you could write

     label3  ; some more code
             ; and some more
     
             jmp label1.loop

   Sometimes it is useful - in a macro, for instance - to be able to
define a label which can be referenced from anywhere but which doesn't
interfere with the normal local-label mechanism. Such a label can't be
non-local because it would interfere with subsequent definitions of,
and references to, local labels; and it can't be local because the
macro that defined it wouldn't know the label's full name. NASM
therefore introduces a third type of label, which is probably only
useful in macro definitions: if a label begins with the special prefix
`..@', then it does nothing to the local label mechanism. So you could
code

     label1:                         ; a non-local label
     .local:                         ; this is really label1.local
     ..@foo:                         ; this is a special symbol
     label2:                         ; another non-local label
     .local:                         ; this is really label2.local
     
             jmp     ..@foo          ; this will jump three lines up

   NASM has the capacity to define other special symbols beginning with
a double period: for example, `..start' is used to specify the entry
point in the `obj' output format (see *Note Section 6.2.6::).