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//! Fields which are common to all segment-section and gate descriptors
use shared::PrivilegeLevel;
use shared::segmentation;
/// System-Segment and Gate-Descriptor Types for IA32e mode. When the `S`
/// (descriptor type) flag in a segment descriptor is clear, the descriptor type
/// is a system descriptor.
///
/// See Intel manual 3a, 3.5 "System Descriptor Types", and Table 3-2,
/// System-Segment and Gate-Descriptor Types".
#[repr(u8)]
pub enum SystemType {
// Reserved = 0
TssAvailable = 1,
/// Only for 16-bit
LocalDescriptorTable = 2,
TssBusy = 3,
CallGate = 4,
/// Only for 16-bit
TaskGate = 5,
InterruptGate = 6,
TrapGate = 7,
}
/// A high-level representation of a descriptor type. One can convert to and
/// from the `Flags` bitfield to encode/decode an actual descriptor.
#[repr(u8)]
pub enum Type {
SystemDescriptor {
/// false/0: 16-bit
/// true/1: native (32- or 64-bit)
size: bool,
ty: SystemType
},
SegmentDescriptor {
ty: segmentation::Type,
accessed: bool
}
}
impl Type {
pub fn pack(self) -> u8 {
match self {
Type::SystemDescriptor { size, ty } =>
(size as u8) << 3 | (ty as u8) | FLAGS_TYPE_SYS.bits,
Type::SegmentDescriptor { ty, accessed } =>
(accessed as u8) | ty.pack() | FLAGS_TYPE_SEG.bits,
}
}
}
bitflags!{
/// Actual encoding of the flags in byte 6 common to all descriptors.
///
/// See Intel manual 3a, figures 3-8, 6-2, and 6-7.
pub flags Flags: u8 {
/// Descriptor is Present.
const FLAGS_PRESENT = 1 << 7,
// Descriptor privilege level
const FLAGS_DPL_RING_0 = 0b00 << 5,
const FLAGS_DPL_RING_1 = 0b01 << 5,
const FLAGS_DPL_RING_2 = 0b10 << 5,
const FLAGS_DPL_RING_3 = 0b11 << 5,
// Is system descriptor
const FLAGS_TYPE_SYS = 0 << 4,
const FLAGS_TYPE_SEG = 1 << 4,
// System-Segment and Gate-Descriptor Types.
// When the S (descriptor type) flag in a segment descriptor is clear,
// the descriptor type is a system descriptor
// All modes (supporting segments)
const TYPE_SYS_LDT = 0b0_0010,
// Protected Mode and older
const FLAGS_TYPE_SYS_16BIT_TSS_AVAILABLE = 0b0_0001,
const FLAGS_TYPE_SYS_16BIT_TSS_BUSY = 0b0_0011,
const FLAGS_TYPE_SYS_16BIT_CALL_GATE = 0b0_0100,
const FLAGS_TYPE_SYS_16BIT_TASK_GATE = 0b0_0101,
const FLAGS_TYPE_SYS_16BIT_INTERRUPT_GATE = 0b0_0110,
const FLAGS_TYPE_SYS_16BIT_TRAP_GATE = 0b0_0111,
// 64-bit in IA-32e Mode (either submode), 32-bit in Protected Mode
const FLAGS_TYPE_SYS_NATIVE_TSS_AVAILABLE = 0b0_1001,
const FLAGS_TYPE_SYS_NATIVE_TSS_BUSY = 0b0_1011,
const FLAGS_TYPE_SYS_NATIVE_CALL_GATE = 0b0_1100,
const FLAGS_TYPE_SYS_NATIVE_INTERRUPT_GATE = 0b0_1110,
const FLAGS_TYPE_SYS_NATIVE_TRAP_GATE = 0b0_1111,
// Code- and Data-Segment Descriptor Types.
// When the S (descriptor type) flag in a segment descriptor is set,
// the descriptor is for either a code or a data segment.
/// Data or code, accessed
const FLAGS_TYPE_SEG_ACCESSED = 0b1_0001,
const FLAGS_TYPE_DATA = 0b1_0000,
const FLAGS_TYPE_CODE = 0b1_1000,
// Data => permissions
const FLAGS_TYPE_SEG_D_WRITE = 0b1_0010,
const FLAGS_TYPE_SEG_D_EXPAND_DOWN = 0b1_0100,
// Code => permissions
const FLAGS_TYPE_SEG_C_READ = 0b1_0010,
const FLAGS_TYPE_SEG_C_CONFORMING = 0b1_0100,
/// Data Read-Only
const FLAGS_TYPE_SEG_D_RO = FLAGS_TYPE_DATA.bits,
/// Data Read-Only, accessed
const FLAGS_TYPE_SEG_D_ROA = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Data Read/Write
const FLAGS_TYPE_SEG_D_RW = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_WRITE.bits,
/// Data Read/Write, accessed
const FLAGS_TYPE_SEG_D_RWA = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_WRITE.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Data Read-Only, expand-down
const FLAGS_TYPE_SEG_D_ROEXD = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_EXPAND_DOWN.bits,
/// Data Read-Only, expand-down, accessed
const FLAGS_TYPE_SEG_D_ROEXDA = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_EXPAND_DOWN.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Data Read/Write, expand-down
const FLAGS_TYPE_SEG_D_RWEXD = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_WRITE.bits
| FLAGS_TYPE_SEG_D_EXPAND_DOWN.bits,
/// Data Read/Write, expand-down, accessed
const FLAGS_TYPE_SEG_D_RWEXDA = FLAGS_TYPE_DATA.bits
| FLAGS_TYPE_SEG_D_WRITE.bits
| FLAGS_TYPE_SEG_D_EXPAND_DOWN.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Code Execute-Only
const FLAGS_TYPE_SEG_C_EO = FLAGS_TYPE_CODE.bits,
/// Code Execute-Only, accessed
const FLAGS_TYPE_SEG_C_EOA = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Code Execute/Read
const FLAGS_TYPE_SEG_C_ER = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_READ.bits,
/// Code Execute/Read, accessed
const FLAGS_TYPE_SEG_C_ERA = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_READ.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Code Execute-Only, conforming
const FLAGS_TYPE_SEG_C_EOC = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_CONFORMING.bits,
/// Code Execute-Only, conforming, accessed
const FLAGS_TYPE_SEG_C_EOCA = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_CONFORMING.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
/// Code Execute/Read, conforming
const FLAGS_TYPE_SEG_C_ERC = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_READ.bits
| FLAGS_TYPE_SEG_C_CONFORMING.bits,
/// Code Execute/Read, conforming, accessed
const FLAGS_TYPE_SEG_C_ERCA = FLAGS_TYPE_CODE.bits
| FLAGS_TYPE_SEG_C_READ.bits
| FLAGS_TYPE_SEG_C_CONFORMING.bits
| FLAGS_TYPE_SEG_ACCESSED.bits,
}
}
impl Flags {
pub const BLANK: Flags = Flags { bits: 0 };
pub const fn from_priv(dpl: PrivilegeLevel) -> Flags {
Flags { bits: (dpl as u8) << 5 }
}
pub fn from_type(ty: Type) -> Flags {
Flags { bits: ty.pack() }
}
pub const fn const_or(self, other: Self) -> Flags {
Flags { bits: self.bits | other.bits }
}
pub const fn cond(self, cond: bool) -> Flags {
Flags { bits: (-(cond as i8) as u8) & self.bits }
}
pub const fn const_mux(self, other: Self, cond: bool) -> Flags {
self.cond(cond).const_or(other.cond(!cond))
}
}