2.3 KiB
2.3 KiB
gdt.h
Definitions to handle segments (Global Descriptor Table).
Segmentation is deprecated and is only needed for backwards compatibility.
OSDev Wiki: Global Descriptor Table
gdt_selector_E - enum
- Null
- Kernel Code - Readable
- Kernel Data - Readable + Writable
- User Null
- User Code - Readable
- User Data - Readable + Writable
gdt_descriptor_T - struct [packed]
| Name | Type | Description |
|---|---|---|
| size | uint16_t | The tables size in bytes (-1) |
| offset | uint64_t | The virtual address, where the table lies in memory |
gdt_entry_T - struct [packed]
| Name | Type | Description |
|---|---|---|
| limit0 | uint16_t | Can be ignored in long mode |
| base0 | uint16_t | Can be ignored in long mode |
| base1 | uint8_t | Can be ignored in long mode |
| access | uint8_t | Specifies permissions (details in osdev wiki) |
| limit1_flags | uint8_t | The first 4 bits can be ignored and the last 4 specify flags |
| base2 | uint8_t | Can be ignored in long mode |
gdt_T - struct [packed / page aligned]
| Name | Type | Description |
|---|---|---|
| null | gdt_entry_T | The entry for GDT_SELECTOR_NULL |
| kernel_code | gdt_entry_T | The entry for GDT_SELECTOR_KERNEL_CODE |
| kernel_data | gdt_entry_T | The entry for GDT_SELECTOR_KERNEL_DATA |
| user_null | gdt_entry_T | The entry for GDT_SELECTOR_USER_NULL |
| user_code | gdt_entry_T | The entry for GDT_SELECTOR_USER_CODE |
| user_data | gdt_entry_T | The entry for GDT_SELECTOR_USER_DATA |
g_default_gdt - global variable
The systems GDT.
gdt_init - function (void)
Populates and loads g_default_gdt.
This will also set all the data segment registers to 0x10 (Kernel Data) and cs to 0x08 (Kernel Code).