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

as: Assembler XENIX Programming
lntersegment Instructions
The XENIX assembler has redefined call and jump instructions to create a new class of
instructions called intersegment instructions. These allow calls and unconditional jumps
to locations across 8086/286 segment boundaries. {These are physical segments, not the
text, data, and bss segments described earlier.) There are the following intersegment
instructions:
calli
jmpi
reti
The calli and jmpi instructions can have either a locally or globally defined symbol as an
operand. In this case, an appropriate segment address is provided automatically when
the program is linked. If an indirect address operand is used, an appropriate segment
address must be explicitly provided. The reti instruction has operands similar to the ret
instruction.
Input/Output Instructions
The XENIX assembler has modified the in and out instructions to include the new forms
inw and outw. The in and out instructions now operate strictly on byte values; inw and
outw operate on words. Furthermore, these instructions take only one operand--the port
number. The al or ax register is accessed as appropriate and must not be given as an
operand.
80286 Instructions
Assembly language programmers who wish to use 80286 instructions can insert the
binary opcode of a given instruction into the instruction stream using the .byte and
.word directives. For example, the directive
.byte /6a, * 1
places the binary opcode of the pushi (for push immediate) instruction in the instruction
stream. This code is equivalent to the 80286 instruction
pushi * 1
A programmer can also use the power of the C language preprocessor to create macros
for the 80286 instructions. For example, if the macro definition
#define PUSHI(x) .byte /6a, *x
is included in an assembly language source, then the macro call
PUSHI(1)
may be used for a pushi instruction in place of the .byte directive. In this case, you
must invoke the C preprocessor using the cc command to resolve this macro.
Note that privileged 80286 instructions are not available to user programs.
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