gdt.h File Reference

#include <kernel/cpu/tss.h>
#include <sys/defs.h>
#include <stdint.h>

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Data Structures
struct	gdt_desc_t
	GDT descriptor structure. More...
struct	gdt_segment_t
	A single GDT segment descriptor. More...
struct	gdt_long_system_segment_t
	A long mode system segment descriptor, used for TSS and LDT. More...
struct	gdt_t
	The actual GDT structure. More...

Macros
#define	GDT_RING0   0
	Kernel ring.
#define	GDT_RING1   1
	Unused ring.
#define	GDT_RING2   2
	Unused ring.
#define	GDT_RING3   3
	User ring.
#define	GDT_NULL   0
	Null segment selector, unused but the gdt must start with it.
#define	GDT_KERNEL_CODE   0x08
	Kernel code segment selector.
#define	GDT_KERNEL_DATA   0x10
	Kernel data segment selector.
#define	GDT_USER_DATA   0x18
	User data segment selector.
#define	GDT_USER_CODE   0x20
	User code segment selector.
#define	GDT_TSS   0x28
	TSS segment selector.
#define	GDT_CS_RING0   (GDT_KERNEL_CODE | GDT_RING0)
	Value to load into the CS register for kernel code.
#define	GDT_SS_RING0   (GDT_KERNEL_DATA | GDT_RING0)
	Value to load into the SS register for kernel data.
#define	GDT_CS_RING3   (GDT_USER_CODE | GDT_RING3)
	Value to load into the CS register for user code.
#define	GDT_SS_RING3   (GDT_USER_DATA | GDT_RING3)
	Value to load into the SS register for user data.
#define	GDT_ACCESS_ACCESSED   (1 << 0)
	Will be set to 1 when accessed, but its best to set it to 1 manually.
#define	GDT_ACCESS_READ_WRITE    (1 << 1)
	If set on a code segment, its readable. If set on a data segment, its writable./*#end#*‍/.
#define	GDT_ACCESS_DIRECTION_CONFORMING    (1 << 2)
	If set on a data segment, the segment grows downwards. If set on a code segment, conforming./*#end#*‍/.
#define	GDT_ACCESS_EXEC   (1 << 3)
	If set, the segment is a code segment. If clear, its a data segment.
#define	GDT_ACCESS_SYSTEM   (0 << 4)
	Is a system segment.
#define	GDT_ACCESS_DATA_CODE   (1 << 4)
	Is a data or code segment.
#define	GDT_ACCESS_TYPE_LDT   0x2
	Local Descriptor Table. Only used if the SYSTEM bit is 0.
#define	GDT_ACCESS_TYPE_TSS_AVAILABLE   0x9
	Available 64-bit Task State Segment. Only used if the SYSTEM bit is 0.
#define	GDT_ACCESS_TYPE_TSS_BUSY   0xB
	Busy 64-bit Task State Segment. Only used if the SYSTEM bit is 0.
#define	GDT_ACCESS_RING0   (0 << 5)
	Descriptor Privilege Level 0 (kernel).
#define	GDT_ACCESS_RING1   (1 << 5)
	Descriptor Privilege Level 1, unused.
#define	GDT_ACCESS_RING2   (2 << 5)
	Descriptor Privilege Level 2, unused.
#define	GDT_ACCESS_RING3   (3 << 5)
	Descriptor Privilege Level 3 (user).
#define	GDT_ACCESS_PRESENT   (1 << 7)
	Must be 1 for all valid segments.
#define	GDT_FLAGS_NONE   0
	No flags set.
#define	GDT_FLAGS_RESERVED   (1 << 0)
	Must be 0.
#define	GDT_FLAGS_LONG_MODE   (1 << 1)
	If set, its a 64-bit code segment.
#define	GDT_FLAGS_SIZE    (1 << 2)
	If set, its a 32-bit segment. If clear, its a 16-bit segment. Ignored in 64-bit mode./*#end#*‍/.
#define	GDT_FLAGS_4KB   (1 << 3)
	If set, the limit is in 4KiB blocks. If clear, the limit is in bytes.

Functions
void	gdt_load_descriptor (gdt_desc_t *descriptor)
	Loads a GDT descriptor.
void	gdt_init (void)
	Initialize the GDT.
void	gdt_cpu_load (void)
	Load the GDT on the current CPU.
void	gdt_cpu_tss_load (tss_t *tss)
	Load a TSS into the GDT and load it using the ltr instruction on the current CPU.