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Chapter 12 I
Link
Technical Reference
If
you want memory Combine Type to be loaded as
the
last
seg-
ment of your program, you can use
this
method.
Add
MEMORY
between
SEGMENT
and
'MEMORY'
in
the
E
segment
line
above. Note, however,
that
these segments
are
loaded
last
only
because you imposed
this
control on them, not because of any
inherent capability
in
the linker or assembler operations.
Segment
Addresses
The 8088
must
be able to address all segments
in
memory. Any
20-bit number can be addressed. The 8088 represents these
numbers as two 16-bit numbers
(for
example, hex F:12). The F is
a canonical frame address, and
the
12 is the offset.
The canonical frame address is
the
largest frame address or seg-
ment address
that
can contain
the
segment.
An
offset is
the
seg-
ment's location, offset from
the
beginning of
the
canonical frame.
The linker recognizes a segment
by
its
canonical frame address
and
its
offset
within
the
frame.
To
convert
the
address F:12 to a 20-bit number, shift
the
frame
address
left
four
bits
and
add
the
offset
as
shown
in
this
example:
FO
+ 12
1',
I,
I
F:12=
102
(20-bit address)
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How the Linker
Assigns
Addresses
To
assign addresses to segments,
the
linker orders each segment
by segment and class name. On
the
basis of
the
alignment and
size of each segment (assuming
the
segments
are
contiguous),
the
linker assigns a frame address and
an
offset to each seg-
ment. This information is used
for
resolving relocatable refer-
ences. The addresses
start
at
0:0.
253
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