1 files changed, 129 insertions, 0 deletions
diff --git a/kernel/main/gdt.c b/kernel/main/gdt.c
new file mode 100644
index 0000000..9bc8282
--- /dev/null
+++ b/kernel/main/gdt.c
@@ -0,0 +1,129 @@
+#include "main/gdt.h"
+#include "globals.h"
+
+#include "util/debug.h"
+#include "util/printf.h"
+#include "util/string.h"
+
+typedef struct gdt_entry
+{
+    uint16_t ge_limitlo;
+    uint16_t ge_baselo;
+    uint8_t ge_basemid;
+    uint8_t ge_access;
+    uint8_t ge_flags;
+    uint8_t ge_basehi;
+} packed gdt_entry_t;
+
+static gdt_entry_t gdt[GDT_COUNT] CORE_SPECIFIC_DATA;
+
+typedef struct tss_entry
+{
+    uint32_t ts_reserved1;
+    uint64_t ts_rsp0;
+    uint64_t ts_rsp1;
+    uint64_t ts_rsp2;
+    uint64_t ts_reserved2;
+    uint64_t ts_ist1;
+    uint64_t ts_ist2;
+    uint64_t ts_ist3;
+    uint64_t ts_ist4;
+    uint64_t ts_ist5;
+    uint64_t ts_ist6;
+    uint64_t ts_ist7;
+    uint64_t ts_reserved3;
+    uint16_t ts_iopb;
+    uint16_t ts_reserved4;
+} packed tss_entry_t;
+
+typedef struct gdt_location
+{
+    uint16_t gl_size;
+    uint64_t gl_offset;
+} packed gdt_location_t;
+
+static gdt_location_t gdtl = {.gl_size = GDT_COUNT * sizeof(gdt_entry_t),
+                              .gl_offset = (uint64_t)&gdt};
+
+static tss_entry_t tss CORE_SPECIFIC_DATA;
+
+void gdt_init(void)
+{
+    memset(gdt, 0, sizeof(gdt));
+    gdt_set_entry(GDT_KERNEL_TEXT, 0x0, 0xFFFFF, 0, 1, 0, 1);
+    gdt_set_entry(GDT_KERNEL_DATA, 0x0, 0xFFFFF, 0, 0, 0, 1);
+    gdt_set_entry(GDT_USER_TEXT, 0x0, 0xFFFFF, 3, 1, 0, 1);
+    gdt_set_entry(GDT_USER_DATA, 0x0, 0xFFFFF, 3, 0, 0, 1);
+
+    uintptr_t tss_pointer = (uintptr_t)&tss;
+    gdt_set_entry(GDT_TSS, (uint32_t)tss_pointer, sizeof(tss), 0, 1, 0, 0);
+    gdt[GDT_TSS / 8].ge_access &= ~(0b10000);
+    gdt[GDT_TSS / 8].ge_access |= 0b1;
+    gdt[GDT_TSS / 8].ge_flags &= ~(0b10000000);
+
+    uint64_t tss_higher_half = ((uint64_t)tss_pointer) >> 32;
+    memcpy(&gdt[GDT_TSS / 8 + 1], &tss_higher_half, 8);
+
+    memset(&tss, 0, sizeof(tss));
+    tss.ts_iopb = sizeof(tss);
+
+    gdt_location_t *data = &gdtl;
+    int segment = GDT_TSS;
+
+    dbg(DBG_CORE, "Installing GDT and TR\n");
+    __asm__ volatile("lgdt (%0); ltr %1" ::"p"(data), "m"(segment));
+}
+
+void gdt_set_kernel_stack(void *addr) { tss.ts_rsp0 = (uint64_t)addr; }
+
+void gdt_set_entry(uint32_t segment, uint32_t base, uint32_t limit,
+                   uint8_t ring, int exec, int dir, int rw)
+{
+    KASSERT(segment < GDT_COUNT * 8 && 0 == segment % 8);
+    KASSERT(ring <= 3);
+    KASSERT(limit <= 0xFFFFF);
+
+    int index = segment / 8;
+    gdt[index].ge_limitlo = (uint16_t)limit;
+    gdt[index].ge_baselo = (uint16_t)base;
+    gdt[index].ge_basemid = (uint8_t)(base >> 16);
+    gdt[index].ge_basehi = (uint8_t)(base >> 24);
+
+    // For x86-64, set the L bit to indicate a 64-bit descriptor and clear Sz
+    // Having both L and Sz set is reserved for future use
+    gdt[index].ge_flags = (uint8_t)(0b10100000 | (limit >> 16));
+
+    gdt[index].ge_access = 0b10000000;
+    gdt[index].ge_access |= (ring << 5);
+    gdt[index].ge_access |= 0b10000;
+    if (exec)
+    {
+        gdt[index].ge_access |= 0b1000;
+    }
+    if (dir)
+    {
+        gdt[index].ge_access |= 0b100;
+    }
+    if (rw)
+    {
+        gdt[index].ge_access |= 0b10;
+    }
+}
+
+void gdt_clear(uint32_t segment)
+{
+    KASSERT(segment < GDT_COUNT * 8 && 0 == segment % 8);
+    memset(&gdt[segment / 8], 0, sizeof(gdt[segment / 8]));
+}
+
+size_t gdt_tss_info(const void *arg, char *buf, size_t osize)
+{
+    size_t size = osize;
+
+    KASSERT(NULL == arg);
+
+    iprintf(&buf, &size, "TSS:\n");
+    iprintf(&buf, &size, "kstack: 0x%p\n", (void *)tss.ts_rsp0);
+
+    return size;
+}