206 MS-DOS User's Reference
Short
references
Near
self-relative
references
Near
segment-relative
references
Long
references
Link carries
out
rDmpS
for four different references:
• Short
• Near self-relative
• Near segment-relative
• Long
The size
of
the value
to
be
computed
depends
on
the
type
of
reference.
If
link
discovers an
error
in
the
anticipated size
of
a
reference, it displays a
fixup-overflow message. This
error
can
happen, for example, if a program attempts,
by
using a 16-bit
offset,
to
reach an instruction in a segment that has a different
frame address. The
error
can also
occur
if
the
segments in a
group
do
not
fit within a single 64K-byte block
of
memory.
A short reference occurs in JMP instructions that attempt
to
pass
control
to
labeled instructions in
the
same segment
or
group. The
target instruction must
be
no
more
than 128 bytes from
the
point
of
reference. The linker computes a signed, 8-bit
number
for this
reference and displays an
error
message if
the
target instruction
belongs
to
a different segment
or
group
(that
is,
if it has a
dif-
ferent frame address),
or
if
the
target is
more
than 128 bytes dis-
tant
(in
either direction).
A near self-relative reference occurs in instructions which access
data relative
to
the
same segment
or
group. The linker computes a
16-bit offset for this reference and displays an
error
message if
the
data are
not
in the same segment
or
group.
A near segment-relative reference occurs in instructions that
attempt
to
access data in a specified segment
or
group,
or
that is
relative
to
a specified segment register.
Link
computes a 16-bit
offset for this reference and displays an
error
message
if
either
of
the
following conditions exists:
the
offset
of
the
target within
the
specified frame is greater than 64K bytes
or
less than 0,
or
the
beginning
of
the
canonical frame
of
the
target is
not
addressable.
A long reference occurs in
CAll
instructions that attempt
to
access an instruction in another segment
or
group.
Link
com-
putes a 16-bit frame address and 16-bit offset for this reference
and displays an
error
message
if
either
of
the
following conditions
exists:
the
computed offset is greater than 64K bytes
or
less than
0,
or
the
beginning
of
the
canonical frame
of
the target
is
not
addressable.
c
c
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