"leilei" wrote:
....
>> A MOV GS, with whatsoever value wont raise an exception except
>> if the CPU don't got a GS (EXCeption06 on x286 and previous).
>> 512 KB RAM ? mmh, are you sure you have a 486 CPU ?
> Hi, I can assure the CPU is 486.
> I do not understand the 'EXCeption06 on x286 and previous' you just
> mentioned. can you give me more information?
FS,GS weren't available on 286 and earlier, so these opcodes were
treated as 'illegal' (EXC06).
But anyway my statement is wrong because I assumed a defined GDT ...
so if your GDT is limited to a certain value then any attempt
to load a selector above it will result in EXC0D (GP#13),
and if your selector points to a descriptor which takes further
actions that aren't covered yet, you may see several exceptions
of any kind (stack/task/GP...)
The selector value you have in CX will point to the descriptor
at offset 'CX AND FFF8h' in your GDT if bit2 of CX is zero.
__
wolfgang
Perhaps my short overview is of some use for you:
_________________________________________________________
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Strict//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<!--
translated from page 366 out of the "Holy Book of KESYS" Jan.1999,
Author: Wolfgang Kern, Vienna Austria (LEOC, KESYS-development) >
<title>x86descriptors</title>
<style type="text/css">
<!--
tr {nowrap; font-weight:thin; font-family:Courier New; font-size:11pt; }
td {nowrap; align:center; }
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</style>
</head>
<body bgcolor="#FFFFFF" text="#000000" align="left">
<basefont face="Courier New">
<basefont size="1">
<u>IA32 Descriptors</caption></u>
<table border="1" frame="box" rules="all" bgcolor="#FFFFFF" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td colspan="8">BASE 31..24</td>
<td rowspan="9">
<pre><b><u>
DATA [93][GDT,LDT]</b></u>
G 4Kb granular limit
B 32-bit stack
P present
E expand down (stack)
W writable
A accessed</pre>
</td>
</tr>
<tr> <td>6</td>
<td><b>G</td>
<td><b>B</td>
<td><b>0</td>
<td>x</td>
<td nowrap colspan="4">LIM 19..16</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td colspan="2" style="border-width:medium;border-color:#000000;
border-style:double;">
<b>1 0</td>
<td><b>E</td>
<td><b>W</td>
<td><b>A</td> </tr>
<tr> <td>4</td>
<td rowspan="3" colspan="8">BASE 0..23</td> </tr>
<tr> <td>3</td></tr>
<tr> <td>2</td></tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">LIMIT 0..15</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#FFFFFF" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td colspan="8">BASE 31..24</td>
<td rowspan="9">
<pre><b><u>
CODE [9b][GDT,LDT]</u></b>
G 4Kb granular
B 32-bit
P present
C confirming
R readable
A accessed</pre>
</td></tr>
<tr> <td>6</td>
<td><b>G</td>
<td><b>B</td>
<td><b>0</td>
<td>x</td>
<td nowrap colspan="4">LIM 19..16</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td colspan="2" style="border-width:medium;border-color:#000000;
border-style:double; padding:0px;"><b>1
1</td>
<td><b>C</td>
<td><b>R</td>
<td><b>A</td> </tr>
<tr> <td>4</td>
<td rowspan="3" colspan="8">BASE 0..23</td> </tr>
<tr> <td>3</td></tr>
<tr> <td>2</td></tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">LIMIT 0..15</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td colspan="8">BASE 31..24</td>
<td rowspan="9"><pre><u><b>
TASK-switch [81/89]</u>
[GDT]</b>
G 4Kb granular limit
P present
BT 32-bit
BS task is busy</pre> </td></tr>
<tr> <td>6</td>
<td><b>G</td>
<td><b>0</td>
<td><b>0</td>
<td>x</td>
<td nowrap colspan="4">LIM 19..16</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td
style="border-color:#000000;border-width:medium;border-style:double"><b>0</t
d>
<td><b>BT</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>0 BS 1</td>
</tr>
<tr> <td>4</td>
<td rowspan="3" colspan="8">BASE 0..23</td> </tr>
<tr> <td>3</td></tr>
<tr> <td>2</td></tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">LIMIT 0..15</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td rowspan="2" colspan="8">Linear Address 31..16</td>
<td rowspan="9"><pre><u><b>
LDT [82][GDT]</b></u></td></tr>
<tr> <td>6</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">--</td>
<td style="border-color:#000000;border-width:medium;border-style:double">
<b>0</td>
<td><b>0</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>0 1 0</td>
</tr>
<tr> <td>4</td>
<td colspan="8">reserved</td> </tr>
<tr> <td>3</td>
<td colspan="8">SEGMENT-</td> </tr>
<tr> <td>2</td>
<td colspan="5">SELECTOR</td>
<td>x</td>
<td colspan="2">RPL</td> </tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">Linear Address 15..0</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td rowspan="2" colspan="8">Offset 31..16</td>
<td rowspan="9"><pre><u><b>
Call-GATE [84/8c]
[GDT,LDT]</b></u>
T 32-bit
L LDT (else GDT)
Dwords copied from
callers stack.
</td></tr>
<tr> <td>6</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td style="border-color:#000000;border-width:medium;border-style:double">
<b>0</td>
<td><b>T</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>1 0 0</td>
</tr>
<tr> <td>4</td>
<td colspan="4">0 0 0 0</td>
<td colspan="4">Dwords </td>
</tr>
<tr> <td>3</td>
<td colspan="8">SEGMENT-</td> </tr>
<tr> <td>2</td>
<td colspan="5">SELECTOR</td>
<td>L</td>
<td colspan="2">RPL</td> </tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">Offset 15..0</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td rowspan="2" colspan="8">reserved</td>
<td rowspan="9"><pre><u><b>
TASK-GATE [85/8d]
[GDT,IDT,LDT]</b></u>
T: 32-bit
</td></tr>
<tr> <td>6</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td style="border-color:#000000;border-width:medium;border-style:double">
<b>0</td>
<td><b>T</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>1 0 1</td>
</tr>
<tr> <td>4</td>
<td colspan="8">reserved</td> </tr>
<tr> <td>3</td>
<td colspan="8">SEGMENT-</td> </tr>
<tr> <td>2</td>
<td colspan="5">SELECTOR</td>
<td>x</td>
<td colspan="2">RPL</td> </tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">reserved</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td rowspan="2" colspan="8">Offset 31..16</td>
<td rowspan="9"><pre><u><b>
INT-GATE [86/8e][IDT]</b></u>
T 32-bit
disables IRQ,
TRAP and NT cleared
until IRET
</td></tr>
<tr> <td>6</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td style="border-color:#000000;border-width:medium;border-style:double">
<b>0</td>
<td><b>T</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>1 1 0</td>
</tr>
<tr> <td>4</td>
<td colspan="8">reserved</td> </tr>
<tr> <td>3</td>
<td colspan="8">SEGMENT-</td> </tr>
<tr> <td>2</td>
<td colspan="5">SELECTOR</td>
<td>x</td>
<td colspan="2">RPL</td> </tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">Offset 15..0</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
<table border="1" frame="box" rules="all" bgcolor="#ffffff" height="200"
cellspacing="0" cellpadding="0"
bordercolor="#808080">
<colgroup>
<col width="8">
<col width="24" align="middle" span=8>
<col width="200" align="left" valign="top">
</colgtroup>
<tr> <td>7</td>
<td rowspan="2" colspan="8">Offset 31..16</td>
<td rowspan="9"><pre><u><b>
INT-TRAP [87/8f][IDT]</b></u>
T 32-bit
IRQ-status unchanged,
TRAP and NT cleared
until IRET
</td></tr>
<tr> <td>6</td> </tr>
<tr> <td>5</td>
<td>P</td>
<td colspan="2">DPL</td>
<td style="border-color:#000000;border-width:medium;border-style:double">
<b>0</td>
<td><b>T</td>
<td colspan= "3"
style="border-color:#000000;border-width:medium;border-style:double">
<b>1 1 1</td>
</tr>
<tr> <td>4</td>
<td colspan="8">reserved</td> </tr>
<tr> <td>3</td>
<td colspan="8">SEGMENT-</td> </tr>
<tr> <td>2</td>
<td colspan="5">SELECTOR</td>
<td>x</td>
<td colspan="2">RPL</td> </tr>
<tr> <td>1</td>
<td rowspan="2" colspan="8">Offset 15..0</td> </tr>
<tr><td>0</td></tr>
<tr style="font-size:7pt;">
<td></td>
<td>7</td>
<td>6</td>
<td>5</td>
<td>4</td>
<td>3</td>
<td>2</td>
<td>1</td>
<td>0</td> </tr>
</table>
<br>
</font>
</body>
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