interrupts, timer, keyboard, segments, lots of kernel code

[bootcensus] / src / segm.c

diff --git a/src/segm.c b/src/segm.c
new file mode 100644 (file)
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;
+}
+*/