Segment Alignment - Intel iAPX 86 User Manual

iAPX 86,88 Family Utilities
LINK86 combines all segments with the same complete (segment, class and overlay)
name and combination type (memory, stack, etc.) from all input modules. The
ordering of segments is done on the basis of these combined segments. The manner
in which segments are combined depends on the alignment of the segments (which is
described in the next topic) and a combining attribute associated with the segment.
When we refer to combining segments, we are talking about how the segments will
be loaded in memory,
not
how they will be stored in the output module. The
segments in the LOC86 output module contain addresses that determine where they
will be loaded in memory" The segments reside in the output module in the same
order as they were in the input modules. Figure 1-5 shows the physical relationships
between the input modules, output module, and loaded program.
INPUT
MODULES
SEG A
SEG B
SEG C
SEG D
SEG E
1 - - - - - -
SEG F
OUTPUT
MODULE
ON DISKETTE
SEG A
SEG B
SEG C
SEG D
SEG E
SEG
F
OUTPUT MODULE
LOADED IN
MEMORY
I
SEG B
I
I
SEG E
I
Figure 1-5. Segment Physical Relationships
Segment Alignment
639-5
A segment can have one (and in the case of the inpage attribute, two) of five align-
ment attributes:
• Byte, which means a segment can be located at any address
• Word, which means a segment can be located only at an address that is a
multiple of two, starting from address OH
• Paragraph, which means a segment can be located only at an address that is a
multiple of 16, starting from address 0
• Page, which means a segment can be located only at an address that is a multiple
of 256, starting from address 0
• Inpage, which means a segment can be located at whichever of the preceding
attributes apply, plus must be located so that it does not cross a page boundary
Figure 1-6 shows the segment alignment boundaries.
Any alignment attribute except byte can result in a gap between combined segments.
For example, when two page-aligned segments are combined, there will always be a
gap, unless the first happens to be an exact mUltiple of 256 bytes in length.
In trod uction
1-7