Reference Guide

Chapter 4 59

Assembler Directives and Pseudo-Operations

.ALLOW Directive

When using the .ALLOW directive, a run-time check must be inserted

into the assembly source code. This run-time check should insure that

the code is executing on a PA-RISC processor that supports the feature

or features being used after the .ALLOW directive. See the example below.

An .ALLOW directive without a parameter signals the end of the region

that the previous .ALLOW directive was controlling. Control is returned

to the .LEVEL speciﬁed for the ﬁle.

NOTE The .ALLOW and .LEVEL directives replace the +DA and +DS

command-line compiler options.

Example

The following example shows how to set a range of memory to 0. In

PA-RISC 1.1 architecture, use the stw instruction. In PA-RISC 2.0

architecture, use the more efﬁcient std instruction.

.LEVEL 1.1

; This object file will be marked as a PA 1.1 object file

; Check what version of PA Architecture we are linked for

addil LR'_SYSTEM_ID-$global$,%dp

ldw RR'_SYSTEM_ID-$global$(%r1),%r5

ldi CPU_PA_RISC1_1,%r4

combt,<,n %r4,%r5,$00000002

; 1.1 specific code

$00000001

addib,< 1,%r23,$00000001

stw,ma %r0,4(%r31)

b,n $00000003

; 2.0 specific code

$00000002

.ALLOW 2.0

addib,< 2,%r23,$00000002

std,ma %r0,8(%r31)

.ALLOW

$00000003

; General code