Reference Guide

Chapter 3 41

HP-UX Architecture Conventions

Spaces

code is placed into space register 7 (%sr7). System code is placed into

quadrant three of the system space (offsets 0xC0000000 through

0xFFFFFFFF). Table 3-1 on page 41 shows the memory layout on HP-UX.

Table 3-1 Memory Layout on HP-UX

You can deﬁne spaces other than $TEXT$ and $PRIVATE$ in a program

ﬁle by declaring a special kind of space called an unloadable space.

Unloadable spaces are treated as normal spaces by the linker, but as the

name implies, are not actually loaded when a program is executed.

Unloadable spaces are typically used by compilers to store extra

information within a program ﬁle. The most common example of an

unloadable space is $DEBUG$, which is used to hold symbolic debugging

information.

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

a space relative to the other spaces. The linker places spaces with lower

sort keys in front of spaces with higher sort keys.

The .SPACE directive is used to declare spaces. The assembly language

programmer is not required to ﬁll one space before beginning another.

When a space is ﬁrst declared, the Assembler begins ﬁlling that space.

The .SPACE directive can also be used to return to a previously declared

space, and the Assembler continues to ﬁll it as if there had been no

intervening spaces.

%sr4 %sr5 %sr6 %sr7

0x00000000 Program

code

0x40000000 Program

data stack

Shared

library data

0x80000000 Shared

memory

Shared

library text

0xC0000000 System code