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New page: Descritors are describing System Segments, Memory Segments and Gates. == System Segments == {| {{wikitable}} ! Name ! Bit ! Full Name ! Description |- ! Limit | 0..15 || Limit 0..15 || Me... |
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== System
{| {{wikitable}}
! Name
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|-
! BAddr
| 16..39 || Base Address 0..23||
|-
! Typ
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|-
! DPL
| 45,46 || Descriptor Privilege Level || Specifies which
|-
! P
| 47 || Present|| Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access.
|-
! Limit
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|}
== Memory
{| {{wikitable}}
! Name
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|-
! BAddr
| 16..39 || Base Address 0..23||
|-
! A
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|-
! DPL
| 45,46 || Descriptor Privilege Level || Specifies which
|-
! P
| 47 || Present|| Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access.
|-
! Limit
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|}
== Interrupt Gate Descriptor ==
{| {{wikitable}}
! Name
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| 16..31 || Selector || [[Selector]] that specifies the segment of the function to call.
|-
! Reserved
| 32..35 ||
|-
! 0
| 36..39 || - || Have to be 0.
|-
!
| 40..43 || Gate Type || Possible interrupt gate types :
{| {{wikitable}}
| 0b0101=0x5 || [[#I386 Task Gate|Task gate]]
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|-
! S
| 44 || Storage Segment || <b>= 0</b> for
|-
! DPL
| 45,46 || Descriptor Privilege Level || Gate call protection. Specifies which
|-
! P
| 47 || Present ||
|-
! Offset
| 48..63 || Offset 16..31 || Higher part of the offset.
|}
== Call Gate Descriptor ==
{| {{wikitable}}
! Name
! Bit
! Full Name
! Description
|-
! Offset
| 0..15 || Offset 0..15 || Lower part of the offset address (also known as pointer).
|-
! Selector
| 16..31 || Selector || [[Selector]] that specifies the code segment of the function to call.
|-
! ParamCnt
| 32..35 || uint32_t's to copy || Number of uint32_t stack arguments to copy on stack switch.
|-
! 0
| 36..39 || - || Have to be 0.
|-
! Type
| 40..43 || Gate Type || Possible call gate types :
{| {{wikitable}}
| 0b0100=0x4 || 16-bit [[#I386 Call Gate|Call gate]]
|-
| 0b1100=0xc || 32-bit [[#I386 Call Gate|Call gate]]
|}
|-
! S
| 44 || Storage Segment || <b>= 0</b> for gates.
|-
! DPL
| 45,46 || Descriptor Privilege Level || Gate call protection. Specifies which privilege level the calling process minimum should have.
|-
! P
| 47 || Present || Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access.
|-
! Offset
| 48..63 || Offset 16..31 || Higher part of the offset.
|}
[[Category:X86]]
[[Category:Memory Segmentation]]
|
Latest revision as of 17:32, 10 July 2023
Descriptors are describing System Segments, Memory Segments and Gates.
System Segment Descriptor
Name | Bit | Full Name | Description | ||||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Limit | 0..15 | Limit 0..15 | Memory range. | ||||||||||||
BAddr | 16..39 | Base Address 0..23 | Linear address where the memory range begins. | ||||||||||||
Typ | 40..43 | Descriptor Type | Possible types :
| ||||||||||||
S | 44 | Storage Segment | = 0 for System Segments. | ||||||||||||
DPL | 45,46 | Descriptor Privilege Level | Specifies which privilege level a process minimum must have to use this Descriptor. | ||||||||||||
P | 47 | Present | Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access. | ||||||||||||
Limit | 48..51 | Limit 16..19 | high part of the Limit. | ||||||||||||
AVL | 52 | . | |||||||||||||
0 | 53 | . | |||||||||||||
- | 54 | . | |||||||||||||
G | 55 | . | |||||||||||||
BAddr | 56..63 | Base Address 24..31 | Higher part of the Base Address. |
Memory Segment Descriptor
Name | Bit | Full Name | Description |
---|---|---|---|
Limit | 0..15 | Limit 0..15 | Memory range. |
BAddr | 16..39 | Base Address 0..23 | Linear address where the memory range begins. |
A | 40 | ||
WR | 41 | ||
CE | 42 | ||
EX | 43 | ||
S | 44 | Storage Segment | = 1 for Memory Segments. |
DPL | 45,46 | Descriptor Privilege Level | Specifies which privilege level a process minimum must have to use this Descriptor. |
P | 47 | Present | Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access. |
Limit | 48..51 | Limit 16..19 | high part of the Limit. |
AVL | 52 | . | |
0 | 53 | . | |
B | 54 | . | |
G | 55 | . | |
BAddr | 56..63 | Base Address 24..31 | Higher part of the Base Address. |
Interrupt Gate Descriptor
Name | Bit | Full Name | Description | ||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Offset | 0..15 | Offset 0..15 | Lower part of the offset address (also known as pointer). | ||||||||||
Selector | 16..31 | Selector | Selector that specifies the segment of the function to call. | ||||||||||
Reserved | 32..35 | ||||||||||||
0 | 36..39 | - | Have to be 0. | ||||||||||
Type | 40..43 | Gate Type | Possible interrupt gate types :
| ||||||||||
S | 44 | Storage Segment | = 0 for gates. | ||||||||||
DPL | 45,46 | Descriptor Privilege Level | Gate call protection. Specifies which privilege level the calling process minimum should have. | ||||||||||
P | 47 | Present | Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access. | ||||||||||
Offset | 48..63 | Offset 16..31 | Higher part of the offset. |
Call Gate Descriptor
Name | Bit | Full Name | Description | ||||
---|---|---|---|---|---|---|---|
Offset | 0..15 | Offset 0..15 | Lower part of the offset address (also known as pointer). | ||||
Selector | 16..31 | Selector | Selector that specifies the code segment of the function to call. | ||||
ParamCnt | 32..35 | uint32_t's to copy | Number of uint32_t stack arguments to copy on stack switch. | ||||
0 | 36..39 | - | Have to be 0. | ||||
Type | 40..43 | Gate Type | Possible call gate types :
| ||||
S | 44 | Storage Segment | = 0 for gates. | ||||
DPL | 45,46 | Descriptor Privilege Level | Gate call protection. Specifies which privilege level the calling process minimum should have. | ||||
P | 47 | Present | Set this to 1 to be able to access the segment, otherwise a #NP (Segment not Present) exception is generated on access. | ||||
Offset | 48..63 | Offset 16..31 | Higher part of the offset. |