Describes the structure of segment descriptors. More...

#include <gdt.h>

Collaboration diagram for GDT::SegmentDescriptor:

Public Member Functions
constexpr	SegmentDescriptor (uint64_t val=0)
	!< Merged value; useful for debugging

constexpr	SegmentDescriptor (uintptr_t base, uint32_t limit, bool code, int ring, Size size)
	Constructor for a code/data GDT entry.

Public Attributes
struct {
uint64_t __pad0__: 40
	Ignored (set via `limit_low` and `base_low` )

bool code_accessed: 1
	If set, the code segment was used since the last reset of this value.

bool readable: 1
	If set, the code is readable (otherwise only executable)

bool conforming: 1
	If set, the execution of code from this segment is only allowed when running at a privilege of numerically less than or equal to privilege_level (i.e. the executor has the same or higher privileges). However, the executor's privileges remain unchanged. For nonconforming code segments (i.e., conforming is set to `0`), execution is allowed only if the privileges are equal. Execution will cause a GPF in case of privilege violation.

bool code: 1
	Has to be set to `true`

uint64_t __pad1__: 9
	Ignored (set via `privilege_level` ... `available`)

Size operation_size: 2
	Default address width (`custom` field bit)

uint64_t __pad2__: 0
	Remainder ignored (set via `base_high`)

};
	Fields specific for Code Segment (for debugging purposes)

struct {
uint64_t __pad0__: 40
	Ignored (set via `limit_low` and `base_low`)

bool data_accessed: 1
	If set, the data segment was used since the last reset of this value.

bool writeable: 1
	If set, data is writable (otherwise read only)

bool expand_down: 1
	Growing direction for dynamically growing segments.

bool notData: 1
	Has to be cleared (`false`)

uint64_t __pad1__: 9
	Ignored (set via `privilege_level` ... `available`)

uint64_t reserved: 1
	Reserved, always set to `0`!

bool big: 1
	Size of the stack pointer (`false` = 16 bit, `true` = 32 bit) More...

uint64_t __pad2__: 0
	Remainder ignored.

};
	Fields specific for Data Segment (for debugging purposes)

struct {
uint64_t __pad0__: 40
	Ignored (set voa `limit_low` and `base_low`)

enum Gate gate: 3
	TSS or LDT entry.

bool not16bit: 1
	`false` for 16-bit, `true` for 32-bit/64-bit

uint64_t __pad1__: 0
	Remainder ignored.

};
	Fields specific to the Task State Segment.

uint64_t	limit_low: 16
	Least-significant bits of segment size (influenced by granularity!)

uint64_t	base_low: 24
	Least-significant bits of base address.

uint64_t	type: 4
	Meaning of those 4 bits depends on descriptor_type below.

DescriptorType	descriptor_type: 1
	Descriptor type (influences the meaning of the 3 bits above)

uint64_t	privilege_level: 2
	Ring for this segment.

bool	present: 1
	Entry is valid iff set to `true`

uint64_t	limit_high: 4
	Most-significant bits of segment size.

bool	available: 1
	Bit which can be used for other purposes (in software)

uint64_t	custom: 2
	Meaning of those 2 bits relate to descriptor_type and type.

Granularity	granularity: 1
	Unit used as granularity for the segment limit.

uint64_t	base_high: 8
	most-significant bits of base address

Detailed Description

Describes the structure of segment descriptors.

A data structure that contains size, position, access rights, and purpose of any segment. Segment descriptors are used in both the GDT, as well as in LDTs.

See also: ISDMv3, 3.4.5; Segment Descriptors; AAPMv2, 4.7 Legacy Segment Descriptors

Constructor & Destructor Documentation

◆ SegmentDescriptor() [1/2]

constexpr GDT::SegmentDescriptor::SegmentDescriptor ( uint64_t val = 0 )

inlineconstexpr

!< Merged value; useful for debugging

Constructor for a specific value

◆ SegmentDescriptor() [2/2]

constexpr GDT::SegmentDescriptor::SegmentDescriptor	(	uintptr_t	base,
		uint32_t	limit,
		bool	code,
		int	ring,
		Size	size
	)

inlineconstexpr

Constructor for a code/data GDT entry.

Parameters

base	Base Address of segment
limit	Size of segment
code	Code or data segment
ring	Privilege level
size	Address width

Member Data Documentation

◆

struct { ... } GDT::SegmentDescriptor::@29

Fields specific for Code Segment (for debugging purposes)

See also: ISDMv3, 3.4.5.1; Code- and Data-Segment Descriptor Types

◆

struct { ... } GDT::SegmentDescriptor::@31

Fields specific for Data Segment (for debugging purposes)

See also: ISDMv3, 3.4.5.1; Code- and Data-Segment Descriptor Types

◆

struct { ... } GDT::SegmentDescriptor::@33

Fields specific to the Task State Segment.

See also: ISDMv3, 7.2.2; TSS Descriptor

◆ pad0

uint64_t GDT::SegmentDescriptor::__pad0__

Ignored (set via limit_low and base_low )

Ignored (set voa limit_low and base_low)

Ignored (set via limit_low and base_low)

◆ pad1

uint64_t GDT::SegmentDescriptor::__pad1__

Ignored (set via privilege_level ... available)

Remainder ignored.

◆ pad2

uint64_t GDT::SegmentDescriptor::__pad2__

Remainder ignored (set via base_high)

Remainder ignored.

◆ big

bool GDT::SegmentDescriptor::big

Size of the stack pointer (false = 16 bit, true = 32 bit)

Warning: Has a different meaning in case expand_down is set to 1.

The documentation for this union was generated from the following file:

machine/gdt.h

Public Member Functions

Public Attributes