Define and use segment selector constants

Author: sheep-o

src/arch/i686/gdt.h

@@ -3,6 +3,11 @@
 
 #include <stdint.h>
 
+#define KERNEL_DATA_SEG 0x10
+#define USER_CODE_SEG   0x1B
+#define USER_DATA_SEG   0x23
+#define TSS_SEGMENT_SELECTOR (5 << 3)
+
 struct tss_entry {
     uint32_t prev_tss;    // The previous TSS - with hardware task switching this is used
     uint32_t esp0;        // The stack pointer to load when we change to kernel mode

src/arch/i686/user.c

@@ -191,13 +191,13 @@ void user_init(void) {
     uint32_t esp0 = 0;
     asm volatile ("mov %%esp, %0" : "=r" (esp0));
     tss.esp0 = esp0;
-    tss.ss0 = 0x10;
-    tss.cs = 0x1B;
-    tss.ds = 0x23;
-    tss.es = 0x23;
-    tss.fs = 0x23;
-    tss.gs = 0x23;
-    tss.ss = 0x23;
+    tss.ss0 = KERNEL_DATA_SEG;
+    tss.cs = USER_CODE_SEG;
+    tss.ds = USER_DATA_SEG;
+    tss.es = USER_DATA_SEG;
+    tss.fs = USER_DATA_SEG;
+    tss.gs = USER_DATA_SEG;
+    tss.ss = USER_DATA_SEG;
     asm volatile("ltr %%ax" : : "a"(5 << 3));
 
     jmp_ring3(p1.sp, p1.ip);