Adds GDT SegmentDescriptors.

This commit is contained in:
Felix Queißner 2016-05-05 12:42:55 +02:00
parent dc1166758e
commit 8e247ba638
3 changed files with 96 additions and 1 deletions

View file

@ -45,7 +45,7 @@ kernel-base.ker: $(OBJS)
run:
qemu-system-i386 -kernel kernel-base.ker
qemu-system-i386 -kernel kernel-base.ker -m 64
bnr: kernel-base.ker run

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@ -0,0 +1,83 @@
#pragma once
#include <inttypes.h>
enum class SegmentAccess : uint8_t
{
None = 0,
Accessed = (1 << 0),
Readable = (1<<1),
Writable = (1<<1),
Direction = (1<<2),
Conforming = (1<<2),
Executable = (1 << 3),
Segment = (1 << 4),
Ring0 = 0,
Ring1 = (1<<5),
Ring2 = (1<<6),
Ring3 = (1<<5) | (1<<6),
Present = (1 << 7),
};
static inline SegmentAccess operator | (SegmentAccess lhs, SegmentAccess rhs)
{
return static_cast<SegmentAccess>(static_cast<uint8_t>(lhs) | static_cast<uint8_t>(rhs));
}
static inline SegmentAccess operator & (SegmentAccess lhs, SegmentAccess rhs)
{
return static_cast<SegmentAccess>(static_cast<uint8_t>(lhs) & static_cast<uint8_t>(rhs));
}
struct SegmentDescriptor
{
uint16_t limit0;
uint16_t base0;
uint8_t base1;
SegmentAccess access;
uint8_t limit1 : 4;
uint8_t flags : 4;
uint8_t base2;
uint32_t limit()
{
return this->limit0 | (this->limit1 << 16);
}
void setLimit(uint32_t value)
{
this->limit0 = (value & 0x0FFFF) >> 0;
this->limit1 = (value & 0xFFFFF) >> 16;
}
uint32_t base()
{
return this->base0 | (this->base1 << 16) | (this->base2 << 24);
}
void setBase(uint32_t value)
{
this->base0 = (value & 0x0000FFFF) >> 0;
this->base1 = (value & 0x00FF0000) >> 16;
this->base2 = (value & 0xFF000000) >> 24;
}
} __attribute__((packed));
static_assert(sizeof(SegmentDescriptor) == 8, "SegmentDescriptor must be 8 bytes large.");
class GDT
{
public:
static const uint32_t length = 8;
private:
static SegmentDescriptor descriptors[length];
GDT() = delete;
public:
static SegmentDescriptor & descriptor(uint32_t index);
};

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@ -0,0 +1,12 @@
#include "gdt.hpp"
SegmentDescriptor GDT::descriptors[GDT::length];
SegmentDescriptor & GDT::descriptor(uint32_t index)
{
static SegmentDescriptor invalid;
if(index >= GDT::length) {
return invalid;
}
return GDT::descriptors[index];
}