ARM VERSION 1.2 - Manual (Page 213)

Thumb Instruction Reference
ARM DUI 0068B Copyright © 2000, 2001 ARM Limited. All rights reserved. 5-19
5.2.3 ADD and SUB, sp
Increment or decrement sp by an immediate constant.
Syntax
ADD sp, #expr
SUB sp, #expr
where:
expr is an expression that evaluates (at assembly time) to a multiple of 4 in the
range –508 to +508.
Usage
This instruction adds the value of expr to the value from Rp , and places the result in Rd .
Note
An ADD instruction with a negative value for expr assembles to the corresponding SUB
instruction with a positive constant. A SUB instruction with a negative value for expr
assembles to the corresponding ADD instruction with a positive constant.
Be aware of this when looking at disassembly listings.
Condition flags
This instruction does not affect the flags.
Architectures
This instruction is available in all T variants of the ARM architecture.
Examples
ADD sp,#312
SUB sp,#96
SUB sp,#abc+8 ; abc + 8 must evaluate at assembly time to
; a multiple of 4 in the range –508 to +508