Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming Programm ing Commands
CC (continued)
Memory Models
cc can create programs for four different memory models: small, middle, large, and
huge. In addition, small model programs can be pure or impure.
Impure-Text Small Model
These programs occupy one 64K -byte physical segment in which both text
(machine instructions) and data are combined. By default, cc creates impure
small model programs. They can also be created using the -Ms option.
Pure-Text Small Model
These programs occupy two 64K -byte physical segments. Text and data are in
separate segments. The text is read-only and may be shared by several
processes at once. The maximum program size is 128K bytes. Pure small model
programs are created using the -i flag when linking small model programs.
Middle Model
These programs occupy several physical segments when linked, but only one
segment contains data. A text segment is allocated per source module, but all
data segments are combined. Special calls and returns are used to access
functions in other segments. The total amount of text can be any size. Data
must not exceed 64K bytes. Middle models programs are created using the -Mm
·
option. These programs are always pure.
Large Model
These programs occupy several physical segments with both text and data in as
many segments as required. Text is handled as in middle model. Special
addresses are used to access data in other segments. Text and data may be any
size, but no data item may be larger than 64K bytes. Large model programs are
created using the -Ml option. These programs are always pure.
Huge Model
These programs occupy several physical segments with both text and data as in
large model, but arrays may span segments, allowing them to be larger than 64K
bytes. Arrays which span more than two segments (128K bytes) must contain
elem ents whose size in bytes is a power of two. Huge model programs are
created using the -Mh option. These programs are always pure.
Small and middle model object files can be linked only with object files and libraries of
the same model. Large and huge model object files can be linked only with large and
huge model object files and libraries. You cannot combine small, medium, and
large/huge model object files into one executable program. cc automatically selects the
correct small, middle, or large versions of the standard libraries based on the
configuration option. It is up to you to make sure that all of your object files and
private libraries are properly compiled in the appropriate model.
The special calls and returns used in middle and large model programs may affect
execution time, particularly if frequent calls are made to very short routines.
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