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THE
80286
INSTRUCTION SET
In Protected mode,
INT
also resets the Trap Flag. In Protected mode, the precise semantics of the
INT
instruction are given
by
the following:
INTERRUPT
Interrupt vector must
be
within lOT table limits else
#GP
(vector number X
8+2+EXT)
Descriptor
AR
byte must indicate interrupt gate, trap gate,
or
task gate else
#GP(vector
number X
8+2+
EXT)
If INT instruction then gate descriptor DPL must be
2::
CPL else
#GP
(vector number X
8+2+EXT)
Gate must
be
PRESENT else
#NP
(vector number X
8+2+EXT)
If TRAP GATE or INTERRUPT GATE:
Examine
CS
selector and descriptor given
in
the gate descriptor:
Selector must be non-null else
#GP
(EXT)
Selector must be within its descriptor table limits else
#GP
(selector+EXT)
Descriptor
AR
byte must indicate code segment else
#GP
(selector +
EXT)
Segment must
be
PRESENT else
#NP
(selector+
EXT)
If code segment
is
non-conforming and DPL < CPL then
INTERRUPT
TO
INNER PRIVILEGE:
Check
selector and descriptor for new stack
in
current Task State Segment:
Selector
must be non-null else #TS(EXT)
Selector
index must be within its descriptor table limits else
#TS
(SS selector +
EXT)
Selector's RPL must equal DPL of code segment else
#TS
(SS selector+EXT)
Stack segment DPL must equal DPL of code segment else
#TS
(SS
selector+EXT)
Descriptor must indicate writable data segment else
#TS
(SS
selector+
EXT)
Segment must
be
PRESENT else
#SS
(SS
selector+EXT)
New stack must have room for
10 bytes else #SS(O)
IP
must be
in
CS
limit else #GP(O)
Load new
SS
and
SP
value from TSS
Load new
CS
and
IP
value from gate
Load
CS
descriptor
Load
SS
descriptor
Push long pointer to old stack onto new stack
Push return address onto new stack
Set CPL to new code segment DPL
Set RPL of
CS
to CPL
If
INTERRUPT GATE then set the Interrupts Enabled Flag to 0 (disabled)
Set the Trap Flag to 0
Set
the Nested Task Flag to 0
If
code segment
is
conforming
or
code segment DPL = CPL then
INTERRUPT
TO
SAME PRIVILEGE LEVEL:
Current stack
limits must allow pushing 6 bytes else #SS(O)
If
interrupt was caused by fault with error code then
Stack limits must allow push of two more bytes else #SS(O)
IP
must be in
CS
limit else #GP(O)
Push flags onto stack
Push current
CS
selector onto stack
Push return offset onto stack
Load
CS:IP from gate
Load
CS
descriptor
Set the RPL field
of
CS
to CPL
Push error code (if
any)
onto stack
If INTERRUPT GATE then set the Interrupts Enabled Flag to 0 (disabled)
Set the Trap Flag to 0
Set
the Nested Task Flag to 0
Else
#GP
(CS
selector +
EXT)
If TASK GATE:
Examine selector to
TSS, given
in
Task Gate descriptor:
Must specify global
in
the local/global bit else
#GP
(TSS selector)
8-49