X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?a=blobdiff_plain;f=src%2Fsegm.c;fp=src%2Fsegm.c;h=d2f940a6ad235daf4b4c6272a9edb54e1421a5be;hb=a2f94f569a4c99204de02814a20098a71527e913;hp=0000000000000000000000000000000000000000;hpb=d1e8a437c1fab4535f82c4c214ec3330ac32e48d;p=bootcensus

diff --git a/src/segm.c b/src/segm.c
new file mode 100644
index 0000000..d2f940a
--- /dev/null
+++ b/src/segm.c
@@ -0,0 +1,124 @@
+#include <string.h>
+#include "segm.h"
+#include "desc.h"
+#include "tss.h"
+
+/* bits for the 3rd 16bt part of the descriptor */
+#define BIT_ACCESSED	(1 << 8)
+#define BIT_WR			(1 << 9)
+#define BIT_RD			(1 << 9)
+#define BIT_EXP_DOWN	(1 << 10)
+#define BIT_CONFORMING	(1 << 10)
+#define BIT_CODE		(1 << 11)
+#define BIT_NOSYS		(1 << 12)
+#define BIT_PRESENT		(1 << 15)
+/* TSS busy bit */
+#define BIT_BUSY		(1 << 9)
+
+/* bits for the last 16bit part of the descriptor */
+#define BIT_BIG			(1 << 6)
+#define BIT_DEFAULT		(1 << 6)
+#define BIT_GRAN		(1 << 7)
+
+enum {TYPE_DATA, TYPE_CODE};
+
+/* we need the following bit pattern at the 8th bit excluding the busy bit: 1001 */
+#define TSS_TYPE_BITS	(9 << 8)
+
+static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type);
+static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl);
+
+/* these functions are implemented in segm-asm.S */
+void setup_selectors(uint16_t code, uint16_t data);
+void set_gdt(uint32_t addr, uint16_t limit);
+void set_task_reg(uint16_t tss_selector);
+
+
+/* our global descriptor table */
+static desc_t gdt[6] __attribute__((aligned(8)));
+
+
+void init_segm(void)
+{
+	memset(gdt, 0, sizeof gdt);
+	segm_desc(gdt + SEGM_KCODE, 0, 0xffffffff, 0, TYPE_CODE);
+	segm_desc(gdt + SEGM_KDATA, 0, 0xffffffff, 0, TYPE_DATA);
+	segm_desc(gdt + SEGM_UCODE, 0, 0xffffffff, 3, TYPE_CODE);
+	segm_desc(gdt + SEGM_UDATA, 0, 0xffffffff, 3, TYPE_DATA);
+
+	set_gdt((uint32_t)gdt, sizeof gdt - 1);
+
+	setup_selectors(selector(SEGM_KCODE, 0), selector(SEGM_KDATA, 0));
+}
+
+/* constructs a GDT selector based on index and priviledge level */
+uint16_t selector(int idx, int rpl)
+{
+	return (idx << 3) | (rpl & 3);
+}
+
+void set_tss(uint32_t addr)
+{
+	task_desc(gdt + SEGM_TASK, addr, sizeof(struct task_state) - 1, 3);
+	set_task_reg(selector(SEGM_TASK, 0));
+}
+
+static void segm_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl, int type)
+{
+	desc->d[0] = limit & 0xffff; /* low order 16bits of limit */
+	desc->d[1] = base & 0xffff;  /* low order 16bits of base */
+
+	/* third 16bit part contains the last 8 bits of base, the 2 priviledge
+	 * level bits starting on bit 13, present flag on bit 15, and type bits
+	 * starting from bit 8
+	 */
+	desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
+		BIT_NOSYS | (type == TYPE_DATA ? BIT_WR : (BIT_RD | BIT_CODE));
+
+	/* last 16bit part contains the last nibble of limit, the last byte of
+	 * base, and the granularity and deafult/big flags in bits 23 and 22 resp.
+	 */
+	desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN | BIT_BIG;
+}
+
+static void task_desc(desc_t *desc, uint32_t base, uint32_t limit, int dpl)
+{
+	desc->d[0] = limit & 0xffff;
+	desc->d[1] = base & 0xffff;
+
+	desc->d[2] = ((base >> 16) & 0xff) | ((dpl & 3) << 13) | BIT_PRESENT |
+		TSS_TYPE_BITS; /* XXX busy ? */
+	desc->d[3] = ((limit >> 16) & 0xf) | ((base >> 16) & 0xff00) | BIT_GRAN;
+}
+/*
+static void dbg_print_gdt(void)
+{
+	int i;
+
+	printf("Global Descriptor Table\n");
+	printf("-----------------------\n");
+
+	for(i=0; i<6; i++) {
+		print_desc(gdt + i);
+	}
+}
+
+static void print_desc(desc_t *desc)
+{
+	uint32_t base, limit;
+	int dpl, g, db, l, avl, p, s, type;
+	char *type_str;
+
+	base = (uint32_t)desc->d[1] | ((uint32_t)(desc->d[2] & 0xff) << 16) | ((uint32_t)(desc->d[3] >> 8) << 24);
+	limit = (uint32_t)desc->d[0] | ((uint32_t)(desc->d[3] & 0xf) << 16);
+	dpl = (desc->d[2] >> 13) & 3;
+	type = (desc->d[2] >> 8) & 0xf;
+	g = (desc->d[3] >> 23) & 1;
+	db = (desc->d[3] >> 22) & 1;
+	l = (desc->d[3] >> 21) & 1;
+	avl = (desc->d[3] >> 20) & 1;
+
+	p = (desc->d[2] >> 15) & 1;
+	s = (desc->d[2] >> 12) & 1;
+}
+*/