Add printing GDT entries

kernel/src/arch/x86_64/entry-stivale2.c

@@ -7,6 +7,8 @@
 
 #include <main.h>
 
+#include "gdt.h"
+
 static uint8_t stack[4096] = {0};
 void stivale2_main(struct stivale2_struct *info);
 
@@ -28,7 +30,7 @@ struct stivale2_header header2 = {
 
 void stivale2_main(struct stivale2_struct *info) {
     parse_stivale2(info);
-    print_stivale2_memmap(info);
+    // print_stivale2_memmap(info);
 
     uint64_t* cr3;
     __asm__ __volatile__ (
@@ -39,6 +41,14 @@ void stivale2_main(struct stivale2_struct *info) {
     );
     printf("PAGE TABLE AT: %x\n", cr3);
 
+    struct gdt_ptr pGDT;
+    __asm__ __volatile__("sgdt %0" : : "m"(pGDT) : "memory");
+    printf("GDT: %x (%d)\n", pGDT.base, pGDT.limit);
+    for(int i = 0; i < (pGDT.limit+1)/8; i++) {
+        uint64_t *gdt_ent = pGDT.base + 8*i;
+        printf("GDTent(%d at %x): %x\n", i, gdt_ent, *gdt_ent);
+    }
+
 	char *argv[3] = {"stivale2", info->bootloader_brand, info->bootloader_version};
     kmain(3, argv);
 }

kernel/src/arch/x86_64/gdt.h

@@ -0,0 +1,9 @@
+#include <stdint.h>
+
+struct gdt_ptr
+{
+    uint16_t limit;
+    uint64_t base;
+} __attribute__((packed));
+
+void loadgdt();

kernel/src/arch/x86_64/gdt.nasm

@@ -0,0 +1,16 @@
+section .rodata
+gdt64:
+    dq 0
+.code: equ $-gdt64
+    dq (1<<44) | (1<<47) | (1<<41) | (1<<43) | (1<<53)
+.data: equ $ - gdt64
+    dq (1<<44) | (1<<47) | (1<<41)
+.pointer:
+    dw .pointer - gdt64 - 1
+    dq gdt64
+
+section .text
+global loadgdt
+loadgdt:
+    lgdt [gdt64.pointer]
+