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Commodore PC - Page 275

Commodore PC
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Unk:
A
Unker
203
n
n
n
How
Link
Works
Link
creates
an
executable
file
by
concatenating
a
program's
code
and
data
segments
according
to
the
instructions
in
the
original
source
files.
These
concatenated
segments
form
an
executable
image
that
is
copied
directly into
memory
when
you
run
the
pro
gram.
The
order
and
manner
in
which
the
linker
copies
segments
to
the
executable
file
defines
the
order
and
manner
in
which
it
loads
the
segments
into
memory.
You
can
tell
the
linker
how
to
link
a
program's
segments
by
using
a
SEGMENT
directive
to
supply
segment
attributes,
or
by
using
the
GROUP
directive
to
form
segment
groups.
These
directives
define
group
associations,
classes,
and
align
and
combine
types
that
define
the
order
and
relative
starting
addresses
of
all
seg
ments
in
a
program.
This
information
works
in
addition
to
any
information
you
supply
through
command
line
options.
The
following
sections
explain
the
process
that
link
uses
to
con
catenate
segments
and
resolve
references
to
items
in
memory.
Alignment
of
Segments
The
linker
uses
a
segment's
align
type
to
set
the
starting
address
for
the
segment.
The
align
types
are
byte,
word,
para,
and
page.
These
types
correspond
to
starting
addresses
at
byte,
word,
para
graph,
and
page
boundaries,
representing
addresses
that
are
multi
ples
of
1,
2,
16,
and
256,
respectively.
The
default
align
type
is
para.
When
the
linker
encounters
a
segment,
it
checks
the
align
type
before
copying
the
segment
to
the
executable
file.
If
the
align
type
is
word,
para,
or
page,
the
linker
checks
the
executable
image
to
see
if
the
last
byte
copied
ends
at
an
appropriate
boun
dary.
If
it
doesn't,
link
pads
the
image
with
extra
null
bytes.
Frame
Number
The
linker
computes
a
starting
address
for
each
segment
in
a
pro
gram.
The
starting
address
is
based
on
a
segment's
align
type
and
on
the
size
of
the
segments
already
copied
to
the
executable
file.
The
address
consists
of
an
offset
and
a
canonical
frame
number,
which
specifies
the
address
of
the
first
paragraph
in
memory
that
contains
one
or
more
bytes
of
the
segment.
A
frame
number
is
always
a
multiple
of
16
(a
paragraph
address),
and
the
oflfeet
is
the
number
of
bytes
from
the
start
of
the
paragraph
to
the
first
byte
in
the
segment.
For
byte
and
word
align
types,
the
offset
may
be
nonzero,
but
the
oflfeet
is
always zero
for
para
and
page
align
types.
How
link
aligns
segments
Segment
starting
addresses

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