Chapter 5. Sections and Relocation

33

undefined section

This "section" is a catch all for address references to objects not in the preceding sections.

An idealized example of three relocatable sections follows. The example uses the traditional section

names

.text

and

.data

. Memory addresses are on the horizontal axis.

+     +    +  +

partial program # 1:

|ttttt|dddd|00|

+     +    +  +

text

data bss

seg.

seg. seg.

+   +   +   +

partial program # 2:

|TTT|DDD|000|

+   +   +   +

+  +   +     +  +    +   +     +~~

linked program:

|

|TTT|ttttt|

|dddd|DDD|00000|

+  +   +     +  +    +   +     +~~

addresses:

0 ...

5.3. Assembler Internal Sections

These sections are meant only for the internal use of

as

. They have no meaning at run time. You do not

really need to know about these sections for most purposes; but they can be mentioned in

as

warning

messages, so it might be helpful to have an idea of their meanings to

as

. These sections are used

to permit the value of every expression in your assembly language program to be a section relative

address.

ASSEMBLER INTERNAL LOGIC ERROR!

An internal assembler logic error has been found. This means there is a bug in the assembler.

expr section

The assembler stores complex expression internally as combinations of symbols. When it needs

to represent an expression as a symbol, it puts it in the expr section.

5.4. Sub Sections

Assembled bytes conventionally fall into two sections: text and data. You may have separate groups of

data in named sections that you want to end up near to each other in the object file, even though they

are not contiguous in the assembler source.

as

allows you to use subsections for this purpose. Within

each section, there can be numbered subsections with values from 0 to 8192. Objects assembled into

the same subsection go into the object file together with other objects in the same subsection. For

example, a compiler might want to store constants in the text section, but might not want to have

them interspersed with the program being assembled. In this case, the compiler could issue a

.text

0

before each section of code being output, and a

.text 1

before each group of constants being

output.

Subsections are optional. If you do not use subsections, everything goes in subsection number zero.