1 files changed, 148 insertions, 0 deletions
diff --git a/src/descriptors.c b/src/descriptors.c
new file mode 100644
index 0000000..82b8709
--- /dev/null
+++ b/src/descriptors.c
@@ -0,0 +1,148 @@
+#include "aplos.h"
+
+#define DESCRIPTOR_SIZE 8
+#define IDT_ENTRIES 256
+
+enum {
+	GDT_START,
+		NULL_SEGMENT = GDT_START,
+		KERNEL_CODE_SEGMENT,
+		KERNEL_DATA_SEGMENT,
+		TASK_STATE_SEGMENT,
+		TASK_STATE_SEGMENT_CONT,
+	GDT_END = TASK_STATE_SEGMENT_CONT,
+
+	IDT_START,
+	IDT_END = IDT_START + (2*IDT_ENTRIES) - 1,
+
+	TOTAL_ENTRY_COUNT
+};
+
+enum {
+	TYPE_NULL_SEGMENT = 0x10,
+	TYPE_DATA_SEGMENT = 0x12,
+	TYPE_CODE_SEGMENT = 0x18,
+	TYPE_TSS_SEGMENT  = 0x09,
+	TYPE_IDT          = 0x0E,
+
+	USER_TYPE_MASK = 0x10
+};
+
+struct descriptor
+{
+	int type;
+
+	/* TASK_STATE_SEGMENT */
+	struct encoded_tss_entry *tss;
+
+	/* IDT */
+	void (*isr)(void);
+};
+
+struct encoded_descriptor
+{
+	alignas(DESCRIPTOR_SIZE) uint8_t data[DESCRIPTOR_SIZE];
+};
+static_assert(sizeof(struct encoded_descriptor) == DESCRIPTOR_SIZE);
+
+struct encoded_tss_entry
+{
+	uint8_t data[104]; /* Not part of this is used yet... */
+};
+
+struct table_reg
+{
+	uint8_t data[10];
+};
+static_assert(sizeof(struct table_reg) == 10);
+
+static struct encoded_tss_entry tss;
+
+static struct descriptor entries[TOTAL_ENTRY_COUNT] = {
+	[NULL_SEGMENT] = {
+		.type = TYPE_NULL_SEGMENT
+	},
+	[KERNEL_CODE_SEGMENT] = {
+		.type = TYPE_CODE_SEGMENT
+	},
+	[KERNEL_DATA_SEGMENT] = {
+		.type = TYPE_DATA_SEGMENT
+	},
+	[TASK_STATE_SEGMENT] = {
+		.type = TYPE_TSS_SEGMENT,
+		.tss = &tss,
+	},
+};
+
+static struct encoded_descriptor encoded[nelem(entries)];
+
+static void encode_descriptors(struct table_reg *, uint64_t, uint64_t);
+static void encode_descriptor(struct descriptor *, struct encoded_descriptor *);
+
+void
+setup_descriptors(void)
+{
+	struct table_reg reg;
+
+	disable_interrupts();
+	encode_descriptors(&reg, GDT_START, GDT_END);
+	set_gdt(&reg, DESCRIPTOR_SIZE*KERNEL_CODE_SEGMENT, DESCRIPTOR_SIZE*KERNEL_DATA_SEGMENT, DESCRIPTOR_SIZE*TASK_STATE_SEGMENT);
+
+	for(uint64_t i = IDT_START; i < IDT_END; i += 2)
+		entries[i].type = TYPE_IDT;
+	for(uint64_t i = 0; i < nelem(isr_stubs); i++)
+		entries[IDT_START+i*2].isr = isr_stubs[i];
+
+	encode_descriptors(&reg, IDT_START, IDT_END);
+	set_idt(&reg);
+
+	enable_interrupts();
+}
+
+static void
+encode_descriptors(struct table_reg *reg, uint64_t start, uint64_t end)
+{
+	uint64_t count = 1 + end - start;
+	struct descriptor *d = entries + start;
+	struct encoded_descriptor *e = encoded + start;
+
+
+	memset(e, 0, sizeof(*e) * count);
+	for(uint64_t i = 0; i < count; i++){
+		encode_descriptor(d+i, e+i);
+		if(!(d[i].type & USER_TYPE_MASK))
+			i++; /* System types are twice as big */
+	}
+
+	write_uint16_le(reg->data, count*DESCRIPTOR_SIZE - 1);
+	write_uint64_le(reg->data+2, (uint64_t)e);
+}
+
+static void
+encode_descriptor(struct descriptor *d, struct encoded_descriptor *e)
+{
+	e->data[5] |= d->type&0x1F;		/* Type */
+	e->data[5] |= 1<<7;			/* Present */
+	e->data[6] |= 1<<5;			/* Long mode */
+
+	uint64_t v;
+
+	switch(d->type){
+	case TYPE_TSS_SEGMENT: 
+		write_uint16_le(e->data, sizeof(*d->tss));
+
+		v = (uint64_t)d->tss;
+		write_uint16_le(e->data+2, v & 0xFFFF);
+		e->data[4] = (v >> 16) & 0xFF;
+		e->data[7] = (v >> 24) & 0xFF;
+		write_uint32_le((uint8_t *)(e+1), (v >> 32) & 0xFFFFFFFF);
+		break;
+	case TYPE_IDT:
+		v = (uint64_t)d->isr;
+		write_uint16_le(e->data, v & 0xFFFF);
+		write_uint16_le(e->data+6, (v >> 16) & 0xFFFF);
+		write_uint32_le(e->data+8, (v >> 32) & 0xFFFFFFFF);
+
+		write_uint16_le(e->data+2, DESCRIPTOR_SIZE*KERNEL_CODE_SEGMENT);
+	}	
+}