Reference Guide

42 Chapter 3

HP-UX Architecture Conventions

Subspaces

While a space is a fundamental concept of the architecture, a subspace is

just a logical subdivision of a space. The Assembler places the program's

code and data into subspaces within spaces. Each subspace belongs to

the space that was current when the subspace was ﬁrst declared. The

linker groups subspaces into spaces as it builds an executable program

ﬁle. For more details see the ld(1) entry in the HP-UX Reference. When

the linker combines several relocatable ﬁles, it groups the subspaces

from each ﬁle by name, so that all subspaces with the same name are

placed contiguously in the program.

Attributes

Subspaces have several attributes. The alignment attribute speciﬁes

what memory alignment (in bytes) is required in the virtual address

space. The alignment can be any power of two, from 1 through 4096,

inclusive. Typically, the alignment is 4 or 8 to specify that the beginning

of the subspace must be word or double-word aligned. Normally, the

alignment attribute is computed automatically by the Assembler from

the largest .ALIGN directive used within the subspace.

The quadrant attribute assigns the subspace to one of the four quadrants

of its space. On HP-UX systems, all subspaces in the code space must be

in quadrant 0, and all subspaces in the data space must be in quadrant

The access rights attribute speciﬁes the access rights that should be

given to each physical page in the subspace. On HP-UX systems, all

subspaces in the code space must have access rights of 0x2C (code page

executable at any privilege level). All subspaces in the data space must

have access rights of 0x1F (data page readable and writable at all

privilege levels).

The sort key attribute allows the programmer to control the placement of

a subspace relative to the other subspaces in its space. The linker places

subspaces with lower sort keys in front of subspaces with higher sort

keys.