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

XENIX Programming cc: C Compiler
Creating Small, Middle, Large, and Huge Programs
The cc command supports the creation of programs of a variety of sizes and purposes
using the -Ms, -Mm, -Ml, -Mh, and -i options. These options define the size of a given
program by defining the number of segments in physical memory to be allocated for
your program's use. They also determine how the system loads the program for
execution.
The cc command allows the creation of programs in five different memory models:
impure-text small model, pure-text small model, middle model, large model, and huge
model. Each model defines a different type of program structure and storage.
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
elements 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.
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