Chapter 26.

M680x0 Dependent Features

26.1. M680x0 Options

The Motorola 680x0 version of

as

has a few machine dependent options:

 l

You can use the

 l

option to shorten the size of references to undefined symbols. If you do not

use the

 l

option, references to undefined symbols are wide enough for a full

long

(32 bits).

(Since

as

cannot know where these symbols end up,

as

can only allocate space for the linker to

fill in later. Since

as

does not know how far away these symbols are, it allocates as much space as

it can.) If you use this option, the references are only one word wide (16 bits). This may be useful

if you want the object file to be as small as possible, and you know that the relevant symbols are

always less than 17 bits away.

 register prefix optional

For some configurations, especially those where the compiler normally does not prepend an

underscore to the names of user variables, the assembler requires a

%

before any use of a register

name. This is intended to let the assembler distinguish between C variables and functions named

a0

through

a7

, and so on. The

%

is always accepted, but is not required for certain configurations,

notably

sun3

. The

 register prefix optional

option may be used to permit omitting the

%

even for configurations for which it is normally required. If this is done, it will generally be

impossible to refer to C variables and functions with the same names as register names.

 bitwise or

Normally the character

|

is treated as a comment character, which means that it can not be used

in expressions. The

 bitwise or

option turns

|

into a normal character. In this mode, you must

either use C style comments, or start comments with a

#

character at the beginning of a line.

 base size default 16  base size default 32

If you use an addressing mode with a base register without specifying the size,

as

will nor 

mally use the full 32 bit value. For example, the addressing mode

%a0@(%d0)

is equivalent to

%a0@(%d0:l)

. You may use the

 base size default 16

option to tell

as

to default to us 

ing the 16 bit value. In this case,

%a0@(%d0)

is equivalent to

%a0@(%d0:w)

. You may use the

 base size default 32

option to restore the default behaviour.

 disp size default 16  disp size default 32

If you use an addressing mode with a displacement, and the value of the displacement is not

known,

as

will normally assume that the value is 32 bits. For example, if the symbol

disp

has

not been defined,

as

will assemble the addressing mode

%a0@(disp,%d0)

as though

disp

is

a 32 bit value. You may use the

 disp size default 16

option to tell

as

to instead assume

that the displacement is 16 bits. In this case,

as

will assemble

%a0@(disp,%d0)

as though

disp

is a 16 bit value. You may use the

 disp size default 32

option to restore the default

behaviour.