Describes the structure of segment descriptors. More...

#include <machine/gdt.h>

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	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
};
struct {
uint64_t	: 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	: 9
	Ignored (set via privilege_level ... available).
Size	operation_size: 2
	Default address width (custom field bit).
uint64_t	: 0
	Remainder ignored (set via base_high).
};
	Fields specific for Code Segment (for debugging purposes).
struct {
uint64_t	: 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	: 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).
uint64_t	: 0
	Remainder ignored.
};
	Fields specific for Data Segment (for debugging purposes).
uint64_t	value

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.