ARM VERSION 1.2

Writing ARM and Thumb Assembly Language

Labels

Labels are symbols that represent addresses. The address given by a label is calculated

during assembly.

The assembler calculates the address of a label relative to the origin of the section where

the label is defined. A reference to a label within the same section can use the program

counter plus or minus an offset. This is called program-relative addressing.

Labels can be defined in a map. See Describing data structures with MAP and FIELD

directives on page2-51. You can place the origin of the map in a specified register at

runtime, and references to the label use the specified register plus an offset. This is

called register-relative addressing.

Addresses of labels in other sections are calculated at link time, when the linker has

allocated specific locations in memory for each section.

Local labels

Local labels are a subclass of label. A local label begins with a number in the range

0-99. Unlike other labels, a local label can be defined many times. Local labels are

useful when you are generating labels with a macro. When the assembler finds a

reference to a local label, it links it to a nearby instance of the local label.

The scope of local labels is lim ited by the

AREA

directive. You can use the

ROUT

directive

to limit the scope more tightly.

Refer to the Local labels on page 3-16 for details of:

•the syntax of local label declarations

•how the assembler a ssociates referenc es to local labels with their label s.

Comments

The first semicolon on a line marks the beginning of a comment, except where the

semicolon appears inside a string constant. The end of the line is the end of the

comment. A comment a lone is a valid line . All comments ar e ignored by the ass embler.