Micro Arch2
14
Systems Design & Programming Micro. Arch. II CMPE 310 1 (Feb. 2, 2002) UMBC U M B C UN IV E R S IT Y O F M A R Y L A N D B A L T I M O R E C O U N T Y 1 9 6 6 Protected Mode Memory Addressing Segments are interpreted differently in Protected Mode vs. Real Mode: • Segment register contains a selector that selects a descriptor from the descriptor table. • The descriptor contains information about the segment, e.g., it’s base address, length and access rights. • The offset can be 32-bits. Descriptor Table FFFFFFFF 00000000 DS 0008 Memory System Data Segment ... ... + EBX ... 0000FF00 0000FF00 0000FF88 Selector 00000088 Offset Base
description
processor
Transcript of Micro Arch2
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
1(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Pro
tect
ed M
ode
Mem
ory
Add
ress
ing
Segm
ents
are
inte
rpre
ted
diff
eren
tly in
Pro
tect
ed M
ode
vs. R
eal M
ode:
•Se
gmen
treg
iste
rcon
tain
sa
sele
ctor
that
sele
cts
ade
scri
ptor
from
the
desc
ript
orta
ble.
• T
hede
scri
ptor
con
tain
s in
form
atio
n ab
out t
he s
egm
ent,
e.g.
, it’s
bas
e ad
dres
s,le
ngth
and
acc
ess
righ
ts.
• T
he o
ffse
t can
be
32-b
its.
Des
crip
tor
Tabl
e
FFFF
FFFF
0000
0000
DS 00
08M
emor
y Sy
stem
Dat
aSe
gmen
t
... ...
+
EB
X
... 0
000F
F00
0000
FF00
0000
FF88
Sele
ctor
0000
0088
Off
set
Bas
e
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
2(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
e
•B
ase
addr
ess:
Star
ting
loca
tion
of th
e m
emor
y se
gmen
t.
•L
imit
:L
engt
h of
the
segm
ent m
inus
1.
20-b
its a
llow
s se
gmen
ts u
p to
1 M
B.
Thi
sva
lue
issh
ifte
dby
12bi
tsto
the
left
whe
nth
eG
(Gra
nula
rity
bit)
isse
tto
1.
Lim
it
015
3916
40B
ase
(L15
-L0)
(B23
-B0)
Acc
ess
Rig
hts
4748
(L19
-55
56B
ase
(B31
-B24
)L
16)
01
23
45
67
GD
XU
5152
63
byte
PD
PLS
AT
YPE
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
3(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
eSe
gmen
t Des
crip
tors
: Bits
52-
55•
G b
it:
Whe
n G
=0,
seg
men
ts c
an b
e 1
byte
to 1
MB
in le
ngth
.W
hen
G=
1, s
egm
ents
can
be
4KB
to 4
GB
in le
ngth
.
•U
bit
:U
ser
(OS)
defi
ned
bit.
•D
bit
:In
dica
tes
how
the
inst
ruct
ions
(80
386
and
up)
acce
ss r
egis
ter
and
mem
ory
data
in p
rote
cted
mod
e.•
Whe
n D
=0,
inst
ruct
ions
are
16-
bit i
nstr
uctio
ns, w
ith 1
6-bi
t off
sets
and
16-
bit
regi
ster
s. S
tack
s ar
e as
sum
ed 1
6-bi
t wid
e an
d SP
is u
sed.
• W
hen
D=
1, 3
2-bi
ts a
re a
ssum
ed.
Allo
ws
8086
-802
86 p
rogr
ams
to r
un.
•X
bit
:R
eser
ved
by I
ntel
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
4(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
eSe
gmen
t Des
crip
tors
: Acc
ess
Rig
hts
(Byt
e 5)
:
The
Acc
ess
Rig
hts
(AR
) by
te c
ontr
ols
acce
ss to
a p
rote
cted
mod
e se
gmen
t and
how
the
segm
ent f
unct
ions
in th
e sy
stem
.
PD
PLS
A
A=
0, S
egm
ent n
ot a
cces
sed
A=
1, S
egm
ent h
as b
een
acce
ssed
000
Dat
a, r
ead-
only
001
Dat
a, r
ead/
wri
te
010
Sta
ck, r
ead-
only
S =
0, S
yste
m d
escr
ipto
rS
= 1
, Cod
e, d
ata
or s
tack
Sets
the
desc
. pri
vile
ge le
vel.
P =
0, d
escr
ipto
r is
und
efine
d.P
= 1
, des
crip
tor
cont
ains
a v
alid
base
and
lim
it.
011
Sta
ck, r
ead/
wri
te
100
Cod
e, e
xecu
te-o
nly
101
Cod
e, e
xecu
te/r
ead
110
Cod
e, e
xecu
te-o
nly,
con
form
ing
111
Cod
e, e
xecu
te/r
ead,
con
form
ing
TY
PE
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
5(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
eD
etai
ls:
The
A (
acce
ssed
) bi
t is
set a
utom
atic
ally
by
the
mic
ropr
oces
sor
and
is n
ever
clea
red.
Thi
s al
low
s O
S co
de to
trac
k fr
eque
ncy
of u
sage
.
The
P (
pres
ent)
bit
shou
ld b
e in
terp
rete
d as
“de
scri
ptor
-is-
valid
”.If
this
bit
is 0
, the
mic
ropr
oces
sor
will
refu
se a
ny a
ttem
pts
to u
se th
isde
scri
ptor
in a
n in
stru
ctio
n.
Alth
ough
the
AR
mus
talw
ays
beva
lid,w
hen
P=0,
the
rest
ofth
ede
scri
ptor
can
be u
sed
in a
ny w
ay th
e O
S lik
es.
The
S (s
yste
m)
bit i
ndic
ates
how
the
desc
ript
or is
to b
e in
terp
rete
d.S=
1 in
dica
tes
a sy
stem
des
crip
tor
(mor
e on
this
late
r).
S=0
indi
cate
s a
code
, dat
a or
sta
ck d
escr
ipto
r.
039
40A
cces
sR
ight
s
47
Ava
ilabl
e
63
Ava
ilabl
e
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
6(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
eD
etai
ls:
Non
-sys
tem
(S=
0) s
egm
ents
:•
Typ
e=0:
The
dat
a se
gmen
t is
basi
cally
a R
OM
.•
Typ
e=1:
Bot
h re
ad a
nd w
rite
ope
ratio
ns a
llow
ed.
Cod
e ca
nN
OT
be f
etch
ed a
nd e
xecu
ted
from
eith
er o
f th
ese
segm
ent t
ypes
.
•T
ype=
2 or
3: A
sta
ck s
egm
ent i
s de
fined
ana
logo
usly
to T
ypes
0 a
nd 1
.
How
ever
, the
inte
rpre
tatio
n of
the
limit
field
is d
iffe
rent
.In
this
cas
e, a
ll of
fset
s m
ust b
egr
eate
r th
an th
e lim
it.T
he u
pper
lim
it is
set
to b
ase
addr
ess
+ F
FFF
(with
D=
0) o
r ba
se a
ddre
ss +
FFFF
FFFF
(w
ith D
=1)
.
Thi
s m
eans
the
stac
k se
gmen
tend
s 1
byte
belo
w th
e ba
se a
ddre
ss.
Exp
andi
ng o
f th
e st
ack
segm
ent s
impl
y in
volv
esde
crea
sing
the
limit.
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
7(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Des
crip
tors
in P
rote
cted
Mod
eD
etai
ls:
•T
ype=
4: A
cod
e se
gmen
t with
no
read
per
mis
sion
.T
his
mea
ns n
o co
nsta
nts
are
allo
wed
, sin
ce th
ey c
anno
t be
read
out
.
•T
ype=
5: A
cod
e se
gmen
t in
whi
ch c
onst
ants
may
be
embe
dded
.
In e
ither
cas
e, n
o w
ritin
g (s
elf-
mod
ifyi
ng c
ode)
is p
erm
itted
.
•T
ype=
6 an
d 7:
Ana
logo
us to
Typ
es 4
and
5w
itho
utpr
ivile
ge p
rote
ctio
n.W
e’ll
disc
uss
the
mea
ning
of
“con
form
ing”
soo
n.4GB
0
Bas
e +
FFF
FFFF
F
Bas
e +
lim
itSt
ack
segm
ent a
rea
botto
m
top
Gro
wth
dir
ectio
n
Bas
e
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
8(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
ent
Reg
iste
rs in
Pro
tect
ed M
ode
Inte
rpre
tatio
n:
Des
crip
tor
Inde
x an
dTa
ble
Inde
x (T
I):
The
13bi
tdes
crip
tori
ndex
sele
cts
one
ofup
to8K
desc
ript
ors
inei
ther
the
GD
Tan
d L
DT,
as
spec
ified
by
the
TI
bit.
The
refo
re, t
hese
14
bits
allo
ws
acce
ss to
16K
8-b
yte
desc
ript
ors.
RP
L: T
he d
esir
ed p
rivi
lege
leve
l of
the
prog
ram
.A
cces
s is
gra
nted
if th
e R
PL v
alue
is lo
wer
(hi
gher
in p
rivi
lege
) th
an th
e A
R o
fth
e se
gmen
t. O
ther
wis
e, a
pri
vile
ge v
iola
tion
is is
sued
.
01
23
15Se
lect
or
TI
RPL
RPL
= R
eque
sted
pri
vile
gele
vel.
00 is
hig
hest
and
11
is lo
wes
t.T
I =
0, G
loba
l Des
crip
tor
Tabl
e.T
I =
1, L
ocal
Des
crip
tor
Tabl
e.
13-b
its
Sele
cts
one
of th
e 81
92de
scri
ptor
s.
Des
crip
tor
Inde
x
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
9(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
enta
tion
Add
ress
Tra
nsla
tion
So in
stea
d of
left
shi
ftin
g by
4 b
its in
Rea
l Mod
e to
for
m th
e se
gmen
t add
ress
, we
righ
t shi
ft b
y 3
bits
and
use
the
valu
e as
a ta
ble
inde
x.
Glo
bal D
escr
ipto
r Ta
ble
0100
00
92 1
0 00
00
00 F
F
FFFF
FF
0000
00
1000
00
DS
0 0
0 8
Mem
ory
Syst
em
1000
FF
Dat
aSe
gmen
tL
imit
Bas
e
Acc
ess
righ
ts
Not
e:D
escr
ipto
r 0
is c
alle
d th
eN
UL
Lde
scri
ptor
and
may
not
be u
sed
to a
cces
sm
emor
y.
2... ...
Not
e: th
ere
is n
om
eani
ngas
soci
ated
the
rela
tive
posi
tion
of th
e se
gmen
tde
scri
ptor
s in
the
tabl
e --
unl
ike
page
tabl
es a
sw
e w
ill s
ee.
+
ESI 00
0000
FF
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
10(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
enta
tion
Add
ress
Tra
nsla
tion
The
re a
re a
ctua
lly th
ree
diff
eren
t des
crip
tor
tabl
es,G
DT
,LD
T a
ndID
T.
Exa
ctly
one
GD
T a
ndID
T m
ust b
e de
fined
for
Pro
tect
ed M
ode
oper
atio
n.
• G
loba
l Des
crip
tor
Tabl
e (G
DT
).T
he G
DT
is u
sed
by a
ll pr
ogra
ms.
• L
ocal
Des
crip
tor
Tabl
e (L
DT
).A
n L
DT
can
opt
iona
lly b
e de
fined
on
a pe
r-ta
sk b
asis
and
is u
sed
to e
xpan
dth
e ad
dres
sabl
e ra
nge
of th
e ta
sk.
• In
terr
upt D
escr
ipto
r Ta
ble
(ID
T).
The
ID
T is
a d
irec
t rep
lace
men
t to
the
inte
rrup
t vec
tor
tabl
e us
ed in
808
6sy
stem
s.
Not
eth
atre
fere
nces
toID
Tar
edo
neth
roug
hth
eha
rdw
are
inte
rrup
tmec
hani
sm,a
ndno
t fro
m a
pro
gram
via
a s
elec
tor.
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
11(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
enta
tion
Add
ress
Tra
nsla
tion
Prog
ram
mer
invi
sibl
e re
gist
ers:
The
GD
T a
ndID
T (
and
LD
T)
are
loca
ted
in th
e m
emor
y sy
stem
.
The
add
ress
es o
f th
e G
DT
and
ID
T a
nd th
eir
limits
(up
to 6
4K b
ytes
) ar
e lo
aded
insp
ecia
lreg
iste
rs,G
DT
Ran
dID
TR
,bef
ore
switc
hing
toPr
otec
ted
Mod
eis
poss
ible
.
CS
DS
ES SS FS GS
Segm
ent
regi
ster
sD
escr
ipto
r C
ache
Bas
e A
ddre
ssL
imit
Acc
ess
TR
LD
TR
Bas
e A
ddre
ssL
imit
Acc
ess
Bas
e A
ddre
ssL
imit
Des
crip
tor
Tabl
e A
ddre
sses
GD
TR
IDT
R16
-bits
32-b
its
Sele
ctor
Sele
ctor
Sele
ctor
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
12(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Segm
enta
tion
Add
ress
Tra
nsla
tion
Prog
ram
mer
invi
sibl
e re
gist
ers:
The
oth
er r
egis
ters
enc
lose
d by
the
red-
dotte
d lin
e ar
e pa
rt o
f th
e de
scri
ptor
cach
e.T
heca
che
isus
edto
redu
ceth
enu
mbe
rofa
ctua
lmem
ory
refe
renc
esne
eded
to c
onst
ruct
the
phys
ical
add
ress
.
The
reis
one
cach
ere
gist
erfo
rea
chof
the
6se
gmen
treg
iste
rs,C
S,D
S,et
c.an
dth
e L
DT
R (
Loc
al D
escr
ipto
r Ta
ble
Reg
iste
r) a
nd T
R (
Task
Reg
iste
r) s
elec
tors
.
The
bas
e ad
dres
s, li
mit
and
acce
ss r
ight
s of
the
desc
ript
or a
re lo
aded
fro
mm
emor
y ev
ery
time
the
corr
espo
ndin
gse
lect
orch
ange
s.
The
LD
TR
and
TR
sel
ecto
rs r
efer
to s
peci
alsy
stem
des
crip
tors
in th
e G
DT.
The
se r
egis
ters
pro
vide
har
dwar
e ac
cele
ratio
n su
ppor
t for
task
sw
itchi
ng.
Let
’sfir
stco
nsid
erho
wL
DT
sar
eus
edto
exte
ndth
ead
dres
ssp
ace
ofin
divi
dual
task
s.
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
13(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Loc
al D
escr
ipto
r Ta
bles
The
LD
TR
sele
ctor
inde
xes
a G
DT
syst
em d
escr
ipto
r de
scri
bing
the
segm
ent c
on-
tain
ing
the
LD
T w
hile
the
cach
e st
ores
the
actu
al L
DT
des
crip
tor.
The
LD
TR
sel
ecto
r ca
n be
load
ed w
ith a
new
val
ue w
hen
anot
her
task
is r
un.
FFFF
FF
0000
00
DS
1
GD
TR
LD
TR
Des
crip
tor
LD
T D
escr
ipto
r
Des
crip
tor
Dat
a D
escr
ipto
r
ESI
Data LDT GDT
LD
Tca
che
32-b
it O
ffse
t
Syst
ems
Des
ign
& P
rogr
amm
ing
Mic
ro. A
rch.
II
CM
PE 3
10
14(F
eb. 2
, 200
2)U
MB
CU
M B
C
UNIVERSITY OF M
AR
YL
AN
D B
ALTIM
ORE COUNTY
1 9
6 6
Loc
al D
escr
ipto
r Ta
bles
LD
T S
egm
ent D
escr
ipto
r:
Bit
44: T
he S
flag
is c
lear
to in
dica
te a
n L
DT
des
crip
tor.
Bit
40-4
3:T
heTy
pefie
ldis
exte
nded
to4
bits
(no
Acc
esse
dbi
t).T
ype
2(0
010)
indi
cate
s a
LD
T d
escr
ipto
r.
Bit
47:I
fth
ePr
esen
tbit
isno
tset
(e.g
.the
reis
noL
DT
defin
ed),
the
80x8
6w
illno
t allo
w y
ou to
load
the
LD
TR
with
its
sele
ctor
.
Bit
0-15
, 16-
19:A
lthou
gh th
e lim
it is
stil
l 20
bits
(an
d th
e G
bit
is a
lso
valid
),se
gmen
ts la
rger
than
64K
B d
on’t
mak
e se
nse!
Lim
it0
1539
1640
Bas
e(1
5-0)
(23-
0)P0
0000
10
4748
(19-
5556
Bas
e(3
1-24
)16
)
5152
63
0000
Lim
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