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cleans up gdt code

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This commit is contained in:
Nathan Singer
2025-06-13 14:37:22 -04:00
parent 2ec3e259d8
commit ed2c0a3568
3 changed files with 86 additions and 62 deletions
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8
kernel/arch/gdt/gdt.s
View File

@ -1,8 +1,8 @@
gdtr DW 0 ; limit store
DD 0 ; base storage
global setGdt
setGdt:
global set_gdt
set_gdt:
mov ax, [esp + 4]
mov [gdtr], ax
mov eax, [esp + 8]
@ -10,8 +10,8 @@ setGdt:
lgdt [gdtr]
ret
global reloadSegments
reloadSegments:
global reload_segments
reload_segments:
jmp 0x08:.reload_CS ; 0x08 is a stand in for the code segment
.reload_CS:
mov ax, 0x10 ; stand in for the data segment

87
kernel/arch/gdt/gdt_entry.c
View File

@ -26,8 +26,58 @@
* etc, by going through the CPU permission system (RING 0 - 3)
*/
#define GDT_SIZE 5
// Each define here is for a specific flag in the descriptor.
// Refer to the intel documentation for a description of what each one does.
#define SEG_DESCTYPE(x) ((x) << 0x04) // Descriptor type (0 for system, 1 for code/data)
#define SEG_PRES(x) ((x) << 0x07) // Present
#define SEG_SAVL(x) ((x) << 0x0C) // Available for system use
#define SEG_LONG(x) ((x) << 0x0D) // Long mode
#define SEG_SIZE(x) ((x) << 0x0E) // Size (0 for 16-bit, 1 for 32)
#define SEG_GRAN(x) ((x) << 0x0F) // Granularity (0 for 1B - 1MB, 1 for 4KB - 4GB)
#define SEG_PRIV(x) (((x) & 0x03) << 0x05) // Set privilege level (0 - 3)
#define SEG_DATA_RD 0x00 // Read-Only
#define SEG_DATA_RDA 0x01 // Read-Only, accessed
#define SEG_DATA_RDWR 0x02 // Read/Write
#define SEG_DATA_RDWRA 0x03 // Read/Write, accessed
#define SEG_DATA_RDEXPD 0x04 // Read-Only, expand-down
#define SEG_DATA_RDEXPDA 0x05 // Read-Only, expand-down, accessed
#define SEG_DATA_RDWREXPD 0x06 // Read/Write, expand-down
#define SEG_DATA_RDWREXPDA 0x07 // Read/Write, expand-down, accessed
#define SEG_CODE_EX 0x08 // Execute-Only
#define SEG_CODE_EXA 0x09 // Execute-Only, accessed
#define SEG_CODE_EXRD 0x0A // Execute/Read
#define SEG_CODE_EXRDA 0x0B // Execute/Read, accessed
#define SEG_CODE_EXC 0x0C // Execute-Only, conforming
#define SEG_CODE_EXCA 0x0D // Execute-Only, conforming, accessed
#define SEG_CODE_EXRDC 0x0E // Execute/Read, conforming
#define SEG_CODE_EXRDCA 0x0F // Execute/Read, conforming, accessed
#define GDT_CODE_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(0) | SEG_CODE_EXRD
#define GDT_DATA_PL0 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(0) | SEG_DATA_RDWR
#define GDT_CODE_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(3) | SEG_CODE_EXRD
#define GDT_DATA_PL3 SEG_DESCTYPE(1) | SEG_PRES(1) | SEG_SAVL(0) | \
SEG_LONG(0) | SEG_SIZE(1) | SEG_GRAN(1) | \
SEG_PRIV(3) | SEG_DATA_RDWR
uint64_t gdt[GDT_SIZE];
void set_gdt(unsigned short limit, uint64_t* base);
void reload_segments(void);
uint64_t create_descriptor(uint32_t base, uint32_t limit, uint16_t flag)
{
uint64_t descriptor;
@ -63,11 +113,11 @@ void gdt_init(void)
gdt[0] = create_descriptor(0, 0, 0); // null
gdt[1] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL0)); // kernel code
gdt[2] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL0)); // kernel data
//gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3)); // user code
//gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3)); // user data
gdt[3] = create_descriptor(0, 0x000FFFFF, (GDT_CODE_PL3)); // user code
gdt[4] = create_descriptor(0, 0x000FFFFF, (GDT_DATA_PL3)); // user data
setGdt((sizeof(uint64_t) * GDT_SIZE) - 1, &(gdt[0])); // limit, base
reloadSegments();
set_gdt((sizeof(uint64_t) * GDT_SIZE) - 1, &(gdt[0])); // limit, base
reload_segments();
#ifdef __TESTING__
kinfo("Initialized the GDT");
#endif
@ -76,4 +126,31 @@ void gdt_init(void)
#endif
}
#undef SEG_DESCTYPE
#undef SEG_PRES
#undef SEG_SAVL
#undef SEG_LONG
#undef SEG_SIZE
#undef SEG_GRAN
#undef SEG_PRIV
#undef SEG_DATA_RD
#undef SEG_DATA_RDA
#undef SEG_DATA_RDWR
#undef SEG_DATA_RDWRA
#undef SEG_DATA_RDEXPD
#undef SEG_DATA_RDEXPDA
#undef SEG_DATA_RDWREXPD
#undef SEG_DATA_RDWREXPDA
#undef SEG_CODE_EX
#undef SEG_CODE_EXA
#undef SEG_CODE_EXRD
#undef SEG_CODE_EXRDA
#undef SEG_CODE_EXC
#undef SEG_CODE_EXCA
#undef SEG_CODE_EXRDC
#undef SEG_CODE_EXRDCA
#undef GDT_CODE_PL0
#undef GDT_DATA_PL0
#undef GDT_CODE_PL3
#undef GDT_DATA_PL3
#undef GDT_SIZE