.ALLOW Directive

Syntax

Lines of source code

Discussion

Use the .ALLOW directive with the .LEVEL directive. The Assembler uses the .LEVEL directive to mark the relocatable object file with the proper PA-RISC architecture version level. In the source file, the Assembler emits warning messages whenever a feature is used that is not appropriate for the specified .LEVEL directive.

Use the .ALLOW directive when it is necessary to include features or instructions from a later version of PA-RISC while leaving the relocatable object file marked as an earlier PA-RISC architecture version. For example, use the .ALLOW directive when you need to include PA-RISC 2.0 features or instructions while leaving the relocatable object file marked as a PA-RISC 1.1 architecture version.

	NOTE: A 2.0W parameter is not permitted with .ALLOW, because the code generated for 2.0W(64-bit mode) is incompatible with other levels.

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