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use core::fmt;
use shared::PrivilegeLevel;
/// Specifies which element to load into a segment from
/// descriptor tables (i.e., is a index to LDT or GDT table
/// with some additional flags).
bitflags! {
#[repr(C, packed)]
pub flags SegmentSelector: u16 {
/// Requestor Privilege Level
const RPL_0 = 0b00,
const RPL_1 = 0b01,
const RPL_2 = 0b10,
const RPL_3 = 0b11,
/// Table Indicator (TI) 0 means GDT is used.
const TI_GDT = 0 << 3,
/// Table Indicator (TI) 1 means LDT is used.
const TI_LDT = 1 << 3,
}
}
/// Reload code segment register.
/// Note this is special since we can not directly move
/// to %cs. Instead we push the new segment selector
/// and return value on the stack and use lretq
/// to reload cs and continue at 1:.
pub unsafe fn set_cs(sel: SegmentSelector) {
#[cfg(target_arch="x86")]
#[inline(always)]
unsafe fn inner(sel: SegmentSelector) {
asm!("pushl $0; \
pushl $$1f; \
lretl; \
1:" :: "ri" (sel.bits() as usize) : "{rax}" "memory");
}
#[cfg(target_arch="x86_64")]
#[inline(always)]
unsafe fn inner(sel: SegmentSelector) {
asm!("pushq $0; \
leaq 1f(%rip), %rax; \
pushq %rax; \
lretq; \
1:" :: "ri" (sel.bits() as usize) : "{rax}" "memory");
}
inner(sel)
}
impl SegmentSelector {
/// Create a new SegmentSelector
///
/// # Arguments
/// * `index` index in GDT or LDT array.
///
pub const fn new(index: u16, rpl: PrivilegeLevel) -> SegmentSelector {
SegmentSelector { bits: index << 3 | (rpl as u16) }
}
pub const fn from_raw(bits: u16) -> SegmentSelector {
SegmentSelector { bits: bits }
}
}
impl fmt::Display for SegmentSelector {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let r0 = match self.contains(RPL_0) {
false => "",
true => "Ring 0 segment selector.",
};
let r1 = match self.contains(RPL_1) {
false => "",
true => "Ring 1 segment selector.",
};
let r2 = match self.contains(RPL_2) {
false => "",
true => "Ring 2 segment selector.",
};
let r3 = match self.contains(RPL_3) {
false => "",
true => "Ring 3 segment selector.",
};
let tbl = match self.contains(TI_LDT) {
false => "GDT Table",
true => "LDT Table",
};
write!(f,
"Index {} in {}, {}{}{}{}",
self.bits >> 3,
tbl,
r0,
r1,
r2,
r3)
// write!(f, "Index")
}
}
/// Reload stack segment register.
pub unsafe fn load_ss(sel: SegmentSelector) {
asm!("movw $0, %ss " :: "r" (sel) : "memory");
}
/// Reload data segment register.
pub unsafe fn load_ds(sel: SegmentSelector) {
asm!("movw $0, %ds " :: "r" (sel) : "memory");
}
/// Reload es segment register.
pub unsafe fn load_es(sel: SegmentSelector) {
asm!("movw $0, %es " :: "r" (sel) : "memory");
}
/// Reload fs segment register.
pub unsafe fn load_fs(sel: SegmentSelector) {
asm!("movw $0, %fs " :: "r" (sel) : "memory");
}
/// Reload gs segment register.
pub unsafe fn load_gs(sel: SegmentSelector) {
asm!("movw $0, %gs " :: "r" (sel) : "memory");
}
/// Returns the current value of the code segment register.
pub fn cs() -> SegmentSelector {
let segment: u16;
unsafe { asm!("mov %cs, $0" : "=r" (segment) ) };
SegmentSelector::from_raw(segment)
}
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