LOC
The LOC
directive sets the current location to the value of the
operand field, which may include changing sections. If the operand is a
constant, the section is set to either .data
if the value is
0x2000000000000000
or larger, else it is set to .text
.
Within a section, the current location may only be changed to
monotonically higher addresses. A LOC expression must be a previously
defined symbol or a "pure" constant.
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
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
asymbol IS an_expressionsets 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 provided, 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,buffer2In 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:
buffer1 BYTE 0,0,0,0,0 buffer2 BYTE 0,0,0,0,0 ... tmpreg GREG buffer1 LDOU $42,tmpreg,(buffer2-buffer1)
Global registers allocated with this directive are allocated in order
higher-to-lower within a file. Other than that, the exact order of
register allocation and elimination is undefined. For example, the order
is undefined when more than one file with such directives are linked
together. With the options -x
and --linker-allocated-gregs
,
GREG
directives for two-operand cases like the one mentioned above
can be omitted. Sufficient global registers will then be allocated by the
linker.
BYTE
The BYTE
directive takes a series of operands separated by a comma.
If an operand is a string (see Strings), each character of that string
is emitted as a byte. Other operands must be constant expressions without
forward references, in the range 0...255. If you need operands having
expressions with forward references, use .byte
(see Byte). An
operand can be omitted, defaulting to a zero value.
WYDE
TETRA
OCTA
The directives WYDE
, TETRA
and OCTA
emit constants of
two, four and eight bytes size respectively. Before anything else happens
for the directive, the current location is aligned to the respective
constant-size boundary. If a label is defined at the beginning of the
line, its value will be that after the alignment. A single operand can be
omitted, defaulting to a zero value emitted for the directive. Operands
can be expressed as strings (see Strings), in which case each
character in the string is emitted as a separate constant of the size
indicated by the directive.
PREFIX
The PREFIX
directive sets a symbol name prefix to be prepended to
all symbols (except local symbols, see MMIX-Symbols), that are not
prefixed with :
, until the next PREFIX
directive. Such
prefixes accumulate. For example,
PREFIX a PREFIX b c IS 0defines a symbol
abc
with the value 0.
BSPEC
ESPEC
A pair of BSPEC
and ESPEC
directives delimit a section of
special contents (without specified semantics). Example:
BSPEC 42 TETRA 1,2,3 ESPECThe single operand to
BSPEC
must be number in the range
0...255. The BSPEC
number 80 is used by the GNU binutils
implementation.