Commodore PC - Page 278

206 MS-DOS User's Reference
Link carries out fixups for four different references:
■ Short
■ Near self-relative
■ Near segment-relative
■ Long
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Short references
Near self-relative
references
Near segment-relative
references
Long references
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.
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