--- /dev/null
+/*
+ * Initialize kernel GDT.
+ * Copyright (c) 2001,2004 David H. Hovemeyer <daveho@cs.umd.edu>
+ * $Revision: 1.4 $
+ *
+ * This is free software. You are permitted to use,
+ * redistribute, and modify it as specified in the file "COPYING".
+ */
+
+#include <geekos/kassert.h>
+#include <geekos/segment.h>
+#include <geekos/int.h>
+#include <geekos/tss.h>
+#include <geekos/gdt.h>
+#include <libc/string.h>
+
+#include <geekos/debug.h>
+
+/*
+ * This is defined in lowlevel.asm.
+ */
+extern void Load_GDTR(ushort_t* limitAndBase);
+
+/* ----------------------------------------------------------------------
+ * Data
+ * ---------------------------------------------------------------------- */
+
+/*
+ * Number of entries in the kernel GDT.
+ */
+#define NUM_GDT_ENTRIES 16
+
+/*
+ * This is the kernel's global descriptor table.
+ */
+struct Segment_Descriptor s_GDT[NUM_GDT_ENTRIES];
+/*
+ * Number of allocated GDT entries.
+ */
+static int s_numAllocated = 0;
+
+
+
+
+
+void DumpGDT()
+{
+ int i;
+ PrintBoth("GDT Contents:\n");
+
+ for (i=0;i<NUM_GDT_ENTRIES;i++) {
+ if (s_GDT[i].present) {
+ PrintBoth("%d: base=%u, limit=%u, sizeLow=%u, baseLow=%u, type=%u, system=%u, dpl=%u, preent=%u, sizeHigh=%u, avail=%u, reserved=%u, dbBit=%u, granularity=%u, baseHigh=%u\n",
+ i,
+ (s_GDT[i].baseHigh<<24) + s_GDT[i].baseLow,
+ (s_GDT[i].sizeHigh<<16) + s_GDT[i].sizeLow,
+ s_GDT[i].sizeLow,
+ s_GDT[i].baseLow,
+ s_GDT[i].type,
+ s_GDT[i].system,
+ s_GDT[i].dpl,
+ s_GDT[i].present,
+ s_GDT[i].sizeHigh,
+ s_GDT[i].avail,
+ s_GDT[i].reserved,
+ s_GDT[i].dbBit,
+ s_GDT[i].granularity,
+ s_GDT[i].baseHigh );
+ } else {
+ PrintBoth("%d: Not Present\n",i);
+ }
+ }
+}
+
+
+/* ----------------------------------------------------------------------
+ * Functions
+ * ---------------------------------------------------------------------- */
+
+/*
+ * Allocate an descriptor from the GDT.
+ * Returns null if there are none left.
+ */
+struct Segment_Descriptor* Allocate_Segment_Descriptor(void)
+{
+ struct Segment_Descriptor* result = 0;
+ int i;
+ bool iflag;
+
+ iflag = Begin_Int_Atomic();
+
+ /* Note; entry 0 is unused (thus never allocated) */
+ for (i = 1; i < NUM_GDT_ENTRIES; ++i) {
+ struct Segment_Descriptor *desc = &s_GDT[ i ];
+ if (desc->avail) {
+ ++s_numAllocated;
+ desc->avail = 0;
+ result = desc;
+ break;
+ }
+ }
+
+ End_Int_Atomic(iflag);
+
+ return result;
+}
+
+/*
+ * Free a segment descriptor.
+ */
+void Free_Segment_Descriptor(struct Segment_Descriptor* desc)
+{
+ bool iflag = Begin_Int_Atomic();
+
+ KASSERT(!desc->avail);
+
+ Init_Null_Segment_Descriptor(desc);
+ desc->avail = 1;
+ --s_numAllocated;
+
+ End_Int_Atomic(iflag);
+}
+
+/*
+ * Get the index (int the GDT) of given segment descriptor.
+ */
+int Get_Descriptor_Index(struct Segment_Descriptor* desc)
+{
+ return (int) (desc - s_GDT);
+}
+
+/*
+ * Initialize the kernel's GDT.
+ */
+void Init_GDT(void)
+{
+ ushort_t limitAndBase[3];
+ ulong_t gdtBaseAddr = (ulong_t) s_GDT;
+ struct Segment_Descriptor* desc;
+ int i;
+
+
+ KASSERT(sizeof(struct Segment_Descriptor) == 8);
+
+ /* Clear out entries. */
+ for (i = 0; i < NUM_GDT_ENTRIES; ++i) {
+ desc = &s_GDT[ i ];
+ Init_Null_Segment_Descriptor(desc);
+ desc->avail = 1;
+ }
+
+ /* Kernel code segment. */
+ desc = Allocate_Segment_Descriptor();
+ Init_Code_Segment_Descriptor(
+ desc,
+ 0, /* base address */
+ 0x100000, /* num pages (== 2^20) */
+ 0 /* privilege level (0 == kernel) */
+ );
+ KASSERT(Get_Descriptor_Index(desc) == (KERNEL_CS >> 3));
+
+ /* Kernel data segment. */
+ desc = Allocate_Segment_Descriptor();
+ Init_Data_Segment_Descriptor(
+ desc,
+ 0, /* base address */
+ 0x100000, /* num pages (== 2^20) */
+ 0 /* privilege level (0 == kernel) */
+ );
+ KASSERT(Get_Descriptor_Index(desc) == (KERNEL_DS >> 3));
+
+ Print("GDT: Base=0x%.8x, limit=%d\n", (uint_t)gdtBaseAddr, (uint_t)(sizeof(struct Segment_Descriptor) * NUM_GDT_ENTRIES));
+
+ /* Activate the kernel GDT. */
+ limitAndBase[0] = sizeof(struct Segment_Descriptor) * NUM_GDT_ENTRIES;
+ limitAndBase[1] = gdtBaseAddr & 0xffff;
+ limitAndBase[2] = gdtBaseAddr >> 16;
+ Load_GDTR(limitAndBase);
+}
