Segment Selector: Difference between revisions
Jump to navigation
Jump to search
| [unchecked revision] | [unchecked revision] |
Content deleted Content added
Revolution (talk | contribs) Overhaul article. Its rather short so I don't think any of the prior contents survived. |
m Reverted edits by Melina148 (talk) to last revision by Khaledhammouda |
||
| (10 intermediate revisions by 5 users not shown) | |||
| Line 1: | Line 1: | ||
A '''Segment Selector''' is a 16-bit binary data structure |
A '''Segment Selector''' is a 16-bit binary data structure specific to the [[IA32_Architecture_Family|IA-32]] and [[X86-64|x86-64]] architectures. It is used in '''[[Protected Mode]]''' and '''[[Long Mode]]'''. Its value identifies a segment in either the '''[[Global Descriptor Table]]''' or a '''[[Local Descriptor Table]]'''. It contains three fields and is used in a variety of situations to interact with '''[[Segmentation]]'''. |
||
For more information, see '''Section 3.4.2: Segment Selectors''' and '''Figure 3-6: Segment Selector''' of the Intel Software Developer Manual, Volume 3-A. |
For more information, see '''Section 3.4.2: Segment Selectors''' and '''Figure 3-6: Segment Selector''' of the Intel Software Developer Manual, Volume 3-A. |
||
| Line 15: | Line 15: | ||
|'''RPL''' |
|'''RPL''' |
||
|} |
|} |
||
* '''Index:''' |
* '''Index:''' Bits 3-15 of the Index of the '''GDT''' or '''LDT''' entry referenced by the selector. Since '''[[Global Descriptor Table#Segment Descriptor|Segment Descriptors]]''' are 8 bytes in length, the value of '''Index''' is never unaligned and contains all zeros in the lowest 3 bits. |
||
* '''TI:''' Specifies which descriptor table to use. If clear ('''0''') then the '''GDT''' is used, if set ('''1''') then the '''LDT''' is used. |
* '''TI:''' Specifies which descriptor table to use. If clear ('''0''') then the '''GDT''' is used, if set ('''1''') then the current '''LDT''' is used. |
||
* '''RPL:''' The requested '''[[Security#Rings|Privilege Level]]''' of the selector, determines if the selector is valid during permission checks and may set execution or memory access privilege. |
* '''RPL:''' The requested '''[[Security#Rings|Privilege Level]]''' of the selector, determines if the selector is valid during permission checks and may set execution or memory access privilege. |
||
== Uses == |
== Uses == |
||
| Line 24: | Line 24: | ||
* '''[[Segmentation|Segmentation Registers]]''' |
* '''[[Segmentation|Segmentation Registers]]''' |
||
* The '''[[Interrupt Descriptor Table]]''' |
* The '''[[Interrupt Descriptor Table]]''' |
||
* The '''[[Task State Segment]]''' |
|||
[[Category:X86]] |
|||
[[Category:Memory Segmentation]] |
|||
Latest revision as of 13:38, 7 June 2024
A Segment Selector is a 16-bit binary data structure specific to the IA-32 and x86-64 architectures. It is used in Protected Mode and Long Mode. Its value identifies a segment in either the Global Descriptor Table or a Local Descriptor Table. It contains three fields and is used in a variety of situations to interact with Segmentation.
For more information, see Section 3.4.2: Segment Selectors and Figure 3-6: Segment Selector of the Intel Software Developer Manual, Volume 3-A.
Segment Selector
| 15 3 | 2 | 1 0 |
|---|---|---|
| Index | TI | RPL |
- Index: Bits 3-15 of the Index of the GDT or LDT entry referenced by the selector. Since Segment Descriptors are 8 bytes in length, the value of Index is never unaligned and contains all zeros in the lowest 3 bits.
- TI: Specifies which descriptor table to use. If clear (0) then the GDT is used, if set (1) then the current LDT is used.
- RPL: The requested Privilege Level of the selector, determines if the selector is valid during permission checks and may set execution or memory access privilege.
Uses
Segment Selectors are used in a few locations, including: