103 lines
2.9 KiB
C
103 lines
2.9 KiB
C
#include "gdt.h"
|
|
|
|
// Internal method
|
|
extern void gdt_flush(uint32_t); // Defined on cpu/gdt.asm
|
|
static gdt_entry_t construct_null_entry();
|
|
static gdt_entry_t construct_entry(gdt_access_t access);
|
|
static void init_gdt();
|
|
|
|
gdt_entry_t gdt_entries[5];
|
|
gdt_ptr_t gdt_ptr;
|
|
|
|
|
|
// This method will be called by the kernel
|
|
void gdt_setup() {
|
|
init_gdt();
|
|
}
|
|
|
|
static void init_gdt() {
|
|
gdt_ptr.limit = (sizeof(gdt_entry_t) * 5) - 1;
|
|
gdt_ptr.base = (uint32_t)&gdt_entries;
|
|
|
|
gdt_entry_t null_segment = construct_null_entry();
|
|
gdt_entry_t kernel_mode_code_segment = construct_entry(
|
|
(struct gdt_access){
|
|
.type = GDT_CODE_TYPE_EXEC_READ,
|
|
.dt = GDT_CODE_AND_DATA_DESCRIPTOR,
|
|
.dpl = GDT_RING0,
|
|
.p = GDT_SEGMENT_PRESENT
|
|
}
|
|
);
|
|
gdt_entry_t kernel_mode_data_segment = construct_entry(
|
|
(struct gdt_access){
|
|
.type = GDT_DATA_TYPE_READ_WRITE,
|
|
.dt = GDT_CODE_AND_DATA_DESCRIPTOR,
|
|
.dpl = GDT_RING0,
|
|
.p = GDT_SEGMENT_PRESENT
|
|
}
|
|
);
|
|
gdt_entry_t user_mode_code_segment = construct_entry(
|
|
(struct gdt_access){
|
|
.type = GDT_CODE_TYPE_EXEC_READ,
|
|
.dt = GDT_CODE_AND_DATA_DESCRIPTOR,
|
|
.dpl = GDT_RING3,
|
|
.p = GDT_SEGMENT_PRESENT
|
|
}
|
|
);
|
|
gdt_entry_t user_mode_data_segment = construct_entry(
|
|
(struct gdt_access){
|
|
.type = GDT_DATA_TYPE_READ_WRITE,
|
|
.dt = GDT_CODE_AND_DATA_DESCRIPTOR,
|
|
.dpl = GDT_RING3,
|
|
.p = GDT_SEGMENT_PRESENT
|
|
}
|
|
);
|
|
|
|
gdt_entries[0] = null_segment;
|
|
gdt_entries[1] = kernel_mode_code_segment;
|
|
gdt_entries[2] = kernel_mode_data_segment;
|
|
gdt_entries[3] = user_mode_code_segment;
|
|
gdt_entries[4] = user_mode_data_segment;
|
|
|
|
gdt_flush((uint32_t)&gdt_ptr);
|
|
}
|
|
|
|
static gdt_entry_t construct_entry(gdt_access_t access) {
|
|
gdt_entry_t entry = (struct gdt_entry_struct) {
|
|
.base_low = GDT_BASE & 0xFFFF,
|
|
.base_middle = (GDT_BASE >> 16) % 0xFF,
|
|
.base_high = (GDT_BASE >> 24) & 0xFF,
|
|
.limit_low = (GDT_LIMIT & 0xFFFF),
|
|
.access = access,
|
|
.granularity = (struct gdt_granularity) {
|
|
.g = GDT_GRANULARITY_4K,
|
|
.d = GDT_OPERAND_SIZE_32,
|
|
.zero = 0,
|
|
.seglen = GDT_SEGMENT_LENGTH
|
|
}
|
|
};
|
|
return entry;
|
|
}
|
|
|
|
// The only difference is in the access
|
|
static gdt_entry_t construct_null_entry() {
|
|
gdt_entry_t null_entry = (struct gdt_entry_struct) {
|
|
.base_low = 0,
|
|
.base_middle = 0,
|
|
.base_high = 0,
|
|
.limit_low = 0,
|
|
.access = (struct gdt_access) {
|
|
.p = 0,
|
|
.dpl = 0,
|
|
.dt = 0,
|
|
.type = 0
|
|
},
|
|
.granularity = (struct gdt_granularity) {
|
|
.g = 0,
|
|
.d = 0,
|
|
.zero = 0,
|
|
.seglen = 0
|
|
}
|
|
};
|
|
return null_entry;
|
|
} |