forked from PoliEcho-holding-org/kern
129 lines
3.1 KiB
C
129 lines
3.1 KiB
C
#ifndef _GDT_H
|
|
#define _GDT_H
|
|
|
|
#include <kernel.h>
|
|
|
|
// Privilege levels
|
|
#define DPL_KERNEL 0
|
|
#define DPL_USER 3
|
|
|
|
/*
|
|
* Segment selector explanation (why kcode is 0x08?)
|
|
*
|
|
* Each segment selector must be 16 bits. These bits
|
|
* have the following layout: (example is 0x08)
|
|
* 0000000000001 0 00 (lsb)
|
|
* | | '- Privilege level
|
|
* | '--- Table indicator
|
|
* '------ Index in table
|
|
*
|
|
* Bits 0-1 are the privilege level. x86 has four,
|
|
* where 00 is the highest and 11 is the lowest. Only
|
|
* these two are widely used. 00 being kernel space &
|
|
* 11 being userspace. Bit 3 is the table indicator.
|
|
* 0 means the GDT and 1 means the LDT. This will most
|
|
* likely be 0. Bits 4-15 are the index. This is just
|
|
* which descriptor in the table is used.
|
|
*
|
|
* SO, for the kernel code segment:
|
|
* Privilege is 00 for kernel space, table indicator
|
|
* s 0 for the GDT and the index is one, because it
|
|
* is the second entry in our GDT (after null desc.)
|
|
*/
|
|
#define SEGMENT_SEL(_idx, _tab, _dpl) (\
|
|
(((_dpl) ) & 3) | \
|
|
(((_tab) << 2) & 4) | \
|
|
(((_idx) << 3) ) \
|
|
)
|
|
|
|
/*
|
|
* Entries:
|
|
* 0 Null desc.
|
|
* 1 Kernel code desc.
|
|
* 2 Kernel data desc.
|
|
* 3 User code desc.
|
|
* 4 User data desc.
|
|
* 5 Task State Segment
|
|
*/
|
|
#define GDT_ENTRIES 6
|
|
#define GDT_NULL SEGMENT_SEL(0, 0, 0)
|
|
#define GDT_KERNEL_CODE SEGMENT_SEL(1, 0, DPL_KERNEL)
|
|
#define GDT_KERNEL_DATA SEGMENT_SEL(2, 0, DPL_KERNEL)
|
|
#define GDT_USER_CODE SEGMENT_SEL(3, 0, DPL_USER)
|
|
#define GDT_USER_DATA SEGMENT_SEL(4, 0, DPL_USER)
|
|
#define GDT_TSS SEGMENT_SEL(5, 0, DPL_KERNEL)
|
|
|
|
#define GDT_DESC(_lim, _base, _access, _flags) (struct gdt_entry) { \
|
|
.base_low = (_base) & 0xFFFF, \
|
|
.base_mid = ((_base) >> 16) & 0xFF, \
|
|
.base_high = ((_base) >> 24) & 0xFF, \
|
|
.limit = (_lim) & 0xFFFF, \
|
|
.flags = ((_flags) & 0xF0) | (((_lim) >> 16) & 0x0F), \
|
|
.access = (_access) \
|
|
}
|
|
|
|
/*
|
|
* GDT descriptor/entry explanation
|
|
*
|
|
* 0-15 low 16 bits of limit
|
|
* 15-31 low 16 bits of base
|
|
* 32-39 mid 8 bits of base
|
|
* 40-47 access byte
|
|
* 40 Accessed
|
|
* 41 Read/Write
|
|
* 42 Direction/Conforming
|
|
* 43 Executable
|
|
* 44 Descriptor type
|
|
* 45-46 DPL
|
|
* 47 Present
|
|
* 48-51 high 4 bits of limit
|
|
* 52-55 flags
|
|
* 52 Reserved
|
|
* 53 Long-mode
|
|
* 54 Size (0 - 16-bit, 1 - 32-bit)
|
|
* 55 Granularity (0 - limit in bytes, 1 - limit in pages)
|
|
* 56-63 high 8 bits of base
|
|
*/
|
|
struct gdt_entry {
|
|
uint16_t limit;
|
|
uint16_t base_low;
|
|
uint8_t base_mid;
|
|
uint8_t access;
|
|
uint8_t flags; // low 4 bits are 4 msbs of limit, high 4 bits are flags
|
|
uint8_t base_high;
|
|
} __packed;
|
|
|
|
struct gdt_pointer {
|
|
uint16_t limit;
|
|
uint32_t base;
|
|
} __packed;
|
|
|
|
struct tss_pointer {
|
|
uint16_t prev_task, __reserved0;
|
|
uint32_t esp0;
|
|
uint16_t ss0, __reserved1;
|
|
uint32_t esp1;
|
|
uint16_t ss1, __reserved2;
|
|
uint32_t esp2;
|
|
uint16_t ss2, __reserved3;
|
|
uint32_t cr3;
|
|
uint32_t eip;
|
|
uint32_t eflags;
|
|
uint32_t eax, ecx, edx, ebx, esp, ebp, esi, edi;
|
|
uint16_t es, __reserved4;
|
|
uint16_t cs, __reserved5;
|
|
uint16_t ss, __reserved6;
|
|
uint16_t ds, __reserved7;
|
|
uint16_t fs, __reserved8;
|
|
uint16_t gs, __reserved9;
|
|
uint16_t ldtr;
|
|
uint32_t __reserved10;
|
|
uint16_t iopb;
|
|
uint32_t ssp;
|
|
} __packed;
|
|
|
|
void tss_esp0(uint32_t esp0);
|
|
int gdt_init(void);
|
|
|
|
#endif
|