Struct SegmentDescriptor

pub struct SegmentDescriptor {
    pub base: u64,
    pub limit: u32,
    pub selector: Selector,
    pub access: SegmentAccess,
}

Available on crate feature arch-amd64 only.

A segment descriptor is a data structure in a GDT or LDT that provides the processor with the size and location of a segment, as well as access control and status information. Segment descriptors are typically created by compilers, linkers, loaders, or the operating system or executive, but not application programs.

Fields

base: u64

Defines the location of byte 0 of the segment within the 4-GByte linear address space. Segment base addresses should be aligned to 16-byte boundaries. Although 16-byte alignment is not required, this alignment allows programs to maximize performance by aligning code and data on 16-byte boundaries.

limit: u32

Specifies the size of the segment. The processor interprets the segment limit in one of two ways, depending on the setting of the G (granularity) flag:

• If the granularity flag is clear, the segment size can range from 1 byte to 1 MByte, in byte increments.

• If the granularity flag is set, the segment size can range from 4 KBytes to 4 GBytes, in 4-KByte increments.

The processor uses the segment limit in two different ways, depending on whether the segment is an expand-up or an expand-down segment. For expand-up segments, the offset in a logical address can range from 0 to the segment limit. Offsets greater than the segment limit generate general-protection exceptions (#GP, for all segments other than SS) or stack-fault exceptions (#SS for the SS segment). For expand-down segments, the segment limit has the reverse function; the offset can range from the segment limit plus 1 to FFFFFFFFH or FFFFH, depending on the setting of the B flag. Offsets less than or equal to the segment limit generate general-protection exceptions or stack-fault exceptions. Decreasing the value in the segment limit field for an expanddown segment allocates new memory at the bottom of the segment’s address space, rather than at the top. IA-32 architecture stacks always grow downwards, making this mechanism convenient for expandable stacks.

selector: Selector

The selector of the segment.

access: SegmentAccess

The access rights of the segment.

Trait Implementations

impl Clone for SegmentDescriptor

fn clone(&self) -> SegmentDescriptor

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for SegmentDescriptor

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for SegmentDescriptor

fn default() -> SegmentDescriptor

Returns the “default value” for a type.

impl PartialEq for SegmentDescriptor

fn eq(&self, other: &SegmentDescriptor) -> bool

Tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Rhs) -> bool

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for SegmentDescriptor

impl Eq for SegmentDescriptor

impl StructuralPartialEq for SegmentDescriptor