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Chapter 30. MMIX Dependent Features

An example, which sets the label

prev

to the current location, and updates the current location

to eight bytes forward:

prev LOC @+8

When a LOC has a constant as its operand, a symbol

__.MMIX.start..text

or

__.MMIX.start..data

is defined depending on the address as mentioned above. Each such

symbol is interpreted as special by the linker, locating the section at that address. Note that if

multiple files are linked, the first object file with that section will be mapped to that address (not

necessarily the file with the LOC definition).

LOCAL

Example:

LOCAL external_symbol

LOCAL 42

.local asymbol

This directive operation generates a link time assertion that the operand does not correspond to

a global register. The operand is an expression that at link time resolves to a register symbol or

a number. A number is treated as the register having that number. There is one restriction on the

use of this directive: the pseudo directive must be placed in a section with contents, code or data.

IS

The

IS

directive:

asymbol IS an_expression

sets the symbol

asymbol

to

an_expression

. A symbol may not be set more than once using

this directive. Local labels may be set using this directive, for example:

5H IS @+4

GREG

This directive reserves a global register, gives it an initial value and optionally gives it a symbolic

name. Some examples:

areg GREG

breg GREG data_value

GREG data_buffer

.greg creg, another_data_value

The symbolic register name can be used in place of a (non special) register. If a value isn't pro 

vided, it defaults to zero. Unless the option

 no merge gregs

is specified, non zero registers

allocated with this directive may be eliminated by

as

; another register with the same value used

in its place. Any of the instructions

CSWAP

,

GO

,

LDA

,

LDBU

,

LDB

,

LDHT

,

LDOU

,

LDO

,

LDSF

,

LDTU

,

LDT

,

LDUNC

,

LDVTS

,

LDWU

,

LDW

,

PREGO

,

PRELD

,

PREST

,

PUSHGO

,

STBU

,

STB

,

STCO

,

STHT

,

STOU

,

STSF

,

STTU

,

STT

,

STUNC

,

SYNCD

,

SYNCID

, can have a value nearby an initial value in place of

its second and third operands. Here, "nearby" is defined as within the range 0. . . 255 from the

initial value of such an allocated register.

buffer1 BYTE 0,0,0,0,0

buffer2 BYTE 0,0,0,0,0

...

GREG buffer1

LDOU $42,buffer2

In the example above, the

Y

field of the

LDOUI

instruction (LDOU with a constant Z) will be

replaced with the global register allocated for

buffer1

, and the

Z

field will have the value 5, the

offset from

buffer1

to

buffer2

. The result is equivalent to this code: