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Directives Reference
7-16 Copyright © 2000, 2001 ARM Limited. All rights reserved. ARM DUI 0068B
7.3.3 FIELD
The
FIELD
directive describes space within a storage map that has been defined using the
MAP
directive.
#
is a synonym for
FIELD
.
Syntax
{label} FIELD expr
where:
label
is an optional label. If specified,
label
is assigned the value of the storage
location counter,
{VAR}
. The storage location counter is then incremented
by the value of
expr
.
expr
is an expression that evaluates to the number of bytes to increment the
storage counter.
Usage
If a storage map is set by a
MAP
directive that specifies a base-register, the base register
is implicit in all labels defined by following
FIELD
directives, until the next
MAP
directive.
These register-relative labels can be quoted in load and store instructions (see MAP on
page 7-15).
Note
You must be careful when using
MAP
,
FIELD
, and register-relative labels. See Describing
data structures with MAP and FIELD directives on page 2-51 for more information.
Example
The following example shows how register-relative labels are defined using the
MAP
and
FIELD
directives.
MAP 0,r9 ; set {VAR} to the address stored in r9
FIELD 4 ; increment {VAR} by 4 bytes
Lab FIELD 4 ; set Lab to the address [r9 + 4]
; and then increment {VAR} by 4 bytes
LDR r0,Lab ; equivalent to LDR r0,[r9,#4]