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Clean up descriptor generation code

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This commit is contained in:
Eryn Wells 2016-03-13 12:51:42 -04:00
parent b3c7b28cda
commit 6e2de52aa9
2 changed files with 32 additions and 26 deletions
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52
src/Descriptors.cc
View file

@ -54,24 +54,30 @@ GDT::DescriptorSpec::descriptor()
{
Descriptor descriptor = 0;
const auto g = uint8_t(hasCoarseGranularity);
const auto db = uint8_t(has32BitOperations);
const auto l = uint8_t(hasNative64BitCode);
const auto avl = uint8_t(hasNative64BitCode);
const auto p = uint8_t(isPresent);
const auto dpl = uint8_t(privilegeLevel);
const auto s = uint8_t(isCodeDataSegment);
const auto typ = uint8_t(type);
const auto dpl = uint8_t(privilegeLevel) & 0x3;
const auto typ = uint8_t(type) & 0xF;
descriptor = base & 0xFF000000; // Bits 31:24 of the base address.
descriptor |= (g << 23); // Granularity field
descriptor |= (db << 22); // D/B field
descriptor |= (l << 21); // L field
descriptor |= (avl << 20); // AVL field
if (hasCoarseGranularity) {
descriptor |= (1 << 23); // Granularity field
}
if (has32BitOperations) {
descriptor |= (1 << 22); // D/B field
}
if (hasNative64BitCode) {
descriptor |= (1 << 21); // L field
}
if (available) {
descriptor |= (1 << 20); // AVL field
}
descriptor |= limit & 0x000F0000; // Bits 19:16 of the segment limit.
descriptor |= (p << 15); // P field
if (isPresent) {
descriptor |= (1 << 15); // P field
}
descriptor |= (dpl << 13); // DPL field
descriptor |= (s << 12); // S field
if (isCodeDataSegment) {
descriptor |= (1 << 12); // S field
}
descriptor |= (typ << 8); // Type field: see Type
descriptor |= (base >> 16) & 0x000000FF; // Bits 23:16 of the base address.
@ -162,14 +168,16 @@ IDT::DescriptorSpec::descriptor()
descriptor = offset & 0xFFFF0000;
}
const auto p = uint8_t(isPresent);
const auto dpl = uint8_t(privilegeLevel);
const auto d = uint8_t((type == Type::Task) ? 0 : is32BitGate);
const auto typ = uint8_t(type);
const auto dpl = uint8_t(privilegeLevel) & 0x3;
const auto typ = uint8_t(type) & 0x7;
descriptor |= p << 15;
if (isPresent) {
descriptor |= 1 << 15;
}
descriptor |= dpl << 13;
descriptor |= d << 11;
if (type != Type::Task && is32BitGate) {
descriptor |= 1 << 11;
}
descriptor |= typ << 8;
// Shift everything up by 32 to make room for the lower 4 bytes
@ -216,9 +224,7 @@ IDT::load()
const
{
PseudoDescriptor idt{Size * sizeof(Descriptor) - 1, uint32_t(&mTable)};
asm volatile(
"lidt %0\n"
: : "m" (idt) :);
asm volatile("lidt %0\n" : : "m" (idt));
}
} /* namespace x86 */

6
src/Descriptors.hh
View file

@ -24,7 +24,7 @@ typedef uint64_t Descriptor;
/** Descriptor privilege level. */
enum class DPL {
enum class DPL : uint8_t {
Ring0 = 0x0,
Ring1 = 0x1,
Ring2 = 0x2,
@ -41,7 +41,7 @@ enum class DPL {
struct GDT
{
/** A four bit value describing the type of the segment. */
enum class Type {
enum class Type : uint8_t {
// Data segment types
DataRO = 0x0, // Read-only
DataROA = 0x1, // Read-only, accessed
@ -116,7 +116,7 @@ private:
*/
struct IDT
{
enum class Type {
enum class Type : uint8_t {
Task = 0x5,
Interrupt = 0x6,
Trap = 0x7,