1 files changed, 35 insertions, 0 deletions
diff --git a/i686/lgdt.c b/i686/lgdt.c
new file mode 100644
index 0000000..10781db
--- /dev/null
+++ b/i686/lgdt.c
@@ -0,0 +1,35 @@
+#include "gdt.h"
+
+struct __attribute__((packed)) Pointer {
+  uint16_t limit;
+  uint32_t base;
+};
+
+static struct SegmentDescriptor_t segments[8] __attribute__((aligned(32)));
+
+void
+gdt_install()
+{
+  SegmentDescriptor(&segments[0], 0, 0, 0);                     // null segment
+  SegmentDescriptor(&segments[2], 0, 0xffffffff, 0x9a);         // ktext
+  SegmentDescriptor(&segments[3], 0, 0xffffffff, 0x92);         // kdata
+
+  const struct Pointer ptr = {.limit = sizeof(segments) - 1, .base = (unsigned)&segments};
+  asm volatile("lgdt (%0)" : : "a"(&ptr));
+
+  // load the kernel data segment
+  asm volatile(R"(mov %0, %%ds
+  mov %0, %%es
+  mov %0, %%fs
+  mov %0, %%gs
+  mov %0, %%ss
+)"
+               :
+               : "ax"(kdataDescriptor));
+
+  // load the kernel code segment
+  asm volatile(R"(ljmp %0, $1f
+  1:)"
+               :
+               : "i"(ktextDescriptor));
+}