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GDT Rewritten to be slightly more stable

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This commit is contained in:
Benjamin Kyd
2019-04-28 00:10:47 +01:00
parent 6be1414484
commit fe0a4a6d3b
7 changed files with 44 additions and 34 deletions
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63
kernel/gdt.cpp
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@@ -4,47 +4,58 @@
#include <lib/std/memory.h>
struct SegmentDescriptor_t {
uint16_t limit_0;
uint16_t base_0;
uint8_t base_1;
uint16_t limit_low;
uint16_t base_low;
uint8_t base_middle;
uint8_t access;
uint8_t limit_1:4;
uint8_t flags:4;
uint8_t base_2;
uint8_t granularity0:4;
uint8_t granularity1:4;
uint8_t base_high;
} __attribute__((packed));
SegmentDescriptor_t _GDT[256];
struct GDT_t {
uint16_t limit;
uint32_t base;
} __attribute__((packed));
void lgdt(void* GDT, uint16_t size) {
SegmentDescriptor_t _GDT[5];
GDT_t _GDTptr;
void lgdt(void* base, uint16_t size) {
struct {
uint16_t size;
void* GDT;
} __attribute__((packed)) GDTR = { size, GDT };
uint16_t length;
void* base;
} __attribute__((packed)) GDTR = { size, base };
asm ( "lgdt %0" : : "m"(GDTR) );
}
asm ( "lgdt %0" : : "m"(GDTR) );}
void initGDT() {
memset(&_GDT, 0, sizeof(_GDT));
#define BochsBreak() outw(0x8A00,0x8A00); outw(0x8A00,0x08AE0);
_GDTptr.limit = (sizeof(SegmentDescriptor_t) * 5) - 1;
_GDTptr.base = (uint32_t)&_GDT;
// Leave 0 blank for null segment
// Null segment
setGDTGate(0, 0, 0, 0, 0);
// Code Base 0 limit 32 Access EXEC + RW
setGDT(1, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_EXEC | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
setGDTGate(1, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_EXEC | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
// Data Base 0 Limit 32 Access RW
setGDT(2, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
setGDTGate(2, 0x00000000, 0xFFFFFFFF, GDT_ACCESS_PRESENT | GDT_ACCESS_RW, GDT_FLAG_GR_PAGE | GDT_FLAG_SZ_32B);
lgdt(&_GDT, sizeof(_GDT));
BochsBreak();
SEGMENTS_RELOAD();
}
void setGDT(uint32_t index, uint32_t baseAddr, uint32_t limitAddr, uint8_t accessLvl, uint8_t flags) {
if (index > 256) return;
_GDT[index].base_0 = (baseAddr >> 0) & 0xFFFF;
_GDT[index].base_1 = (baseAddr >> 16) & 0xFF;
_GDT[index].base_2 = (baseAddr>> 24) & 0xFF;
_GDT[index].limit_0 = (limitAddr >> 0) & 0xFFFF;
_GDT[index].limit_1 = (limitAddr >> 16) & 0x0F;
_GDT[index].access = accessLvl;
_GDT[index].flags = flags & 0x0F;
void setGDTGate(uint32_t index, uint32_t baseAddr, uint32_t limitAddr, uint8_t accessLvl, uint8_t flags) {
if (index > 5) return;
_GDT[index].base_low = (baseAddr & 0xFFFF);
_GDT[index].base_middle = (baseAddr >> 16) & 0xFF;
_GDT[index].base_high = (baseAddr >> 24) & 0xFF;
_GDT[index].limit_low = (limitAddr >> 0) & 0xFFFF;
_GDT[index].granularity0 = (limitAddr >> 16) & 0x0F;
_GDT[index].granularity1 = flags & 0x0F;
_GDT[index].access = accessLvl;
}