diff options
Diffstat (limited to 'kernel/cpu/gdt.h')
| -rw-r--r-- | kernel/cpu/gdt.h | 76 |
1 files changed, 76 insertions, 0 deletions
diff --git a/kernel/cpu/gdt.h b/kernel/cpu/gdt.h new file mode 100644 index 0000000..a490dea --- /dev/null +++ b/kernel/cpu/gdt.h @@ -0,0 +1,76 @@ +#ifndef GDT_H +#define GDT_H +#include <stdint.h> +#include <string.h> + +#define GDT_ENTRY_SIZE 0x8 +#define GDT_NULL_SEGMENT 0x0 +#define GDT_KERNEL_CODE_SEGMENT 0x1 +#define GDT_KERNEL_DATA_SEGMENT 0x2 +#define GDT_USERMODE_CODE_SEGMENT 0x3 +#define GDT_USERMODE_DATA_SEGMENT 0x4 +#define GDT_TSS_SEGMENT 0x5 + +struct GDT_Entry +{ + uint16_t limit_low; + uint32_t base_low : 24; + uint32_t accessed : 1; + uint32_t read_write : 1; // readable for code, writable for data + uint32_t conforming_expand_down : 1; // conforming for code, expand down for data + uint32_t code : 1; // 1 for code, 0 for data + uint32_t code_data_segment : 1; // should be 1 for everything but TSS and LDT + uint32_t DPL : 2; // privilege level + uint32_t present : 1; + uint32_t limit_high : 4; + uint32_t available : 1; // only used in software; has no effect on hardware + uint32_t long_mode : 1; + uint32_t big : 1; // 32-bit opcodes for code, uint32_t stack for data + uint32_t gran : 1; // 1 to use 4k page addressing, 0 for byte addressing + uint8_t base_high; +}__attribute__((packed)); + +typedef struct GDT_Pointer +{ + uint16_t size; + uint32_t offset; +}__attribute__((packed)) GDT_Pointer; + +struct tss_entry_struct +{ + uint32_t prev_tss; // The previous TSS - with hardware task switching these form a kind of backward linked list. + uint32_t esp0; // The stack pointer to load when changing to kernel mode. + uint32_t ss0; // The stack segment to load when changing to kernel mode. + // Everything below here is unused. + uint32_t esp1; // esp and ss 1 and 2 would be used when switching to rings 1 or 2. + uint32_t ss1; + uint32_t esp2; + uint32_t ss2; + uint32_t cr3; + uint32_t eip; + uint32_t eflags; + uint32_t eax; + uint32_t ecx; + uint32_t edx; + uint32_t ebx; + uint32_t esp; + uint32_t ebp; + uint32_t esi; + uint32_t edi; + uint32_t es; + uint32_t cs; + uint32_t ss; + uint32_t ds; + uint32_t fs; + uint32_t gs; + uint32_t ldt; + uint16_t trap; + uint16_t iomap_base; +} __attribute__((packed)); + +void gdt_init(); + +uint8_t gen_access_byte(uint8_t priv, uint8_t s, uint8_t ex, uint8_t dc, uint8_t rw); +uint64_t gen_gdt_entry(uint32_t base, uint32_t limit, uint8_t access_byte, uint8_t flag); +uint8_t gen_flag(uint8_t gr, uint8_t sz); +#endif |