sp1/amd64: cpu: Add GDT sources

Signed-off-by: Ian Moffett <ian@mirocom.org>

usr/src/sp1/amd64/cpu/locore.S

@@ -37,9 +37,90 @@ md_cpu_init:
     or $1<<11, %eax         // Set NXE
     wrmsr                   // Write it back
 
+    lea g_GDTR(%rip), %rdi
+    call md_gdt_load
+
     pop %rbx
     pop %r15
     pop %r14
     pop %r13
     pop %r12
     retq
+
+    .text
+    .globl md_gdt_load
+md_gdt_load:
+    push %r12
+    push %r13
+    push %r14
+    push %r15
+    push %rbx
+    push %rbp
+
+    lgdt (%rdi)                 /* Load our own GDT */
+    push $0x08                  /* Kernel CS */
+    lea 1f(%rip), %rbx          /* Drop point */
+    push %rbx                   /* RIP */
+    lretq                       /* Flush prefetch + reload CS */
+1:  mov $0x10, %ax              /* Kernel DS */
+    mov %ax, %ds
+    mov %ax, %es
+    mov %ax, %ss
+    mov %ax, %fs
+    xor %ax, %ax
+    mov %ax, %gs
+
+    pop %rbp
+    pop %rbx
+    pop %r15
+    pop %r14
+    pop %r13
+    pop %r12
+    retq
+
+     .section .data
+    .globl g_GDT
+g_GDT:
+.NULL:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b00000000
+    .byte 0b00000000
+    .byte 0x00
+.CODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10011010
+    .byte 0b00100000
+    .byte 0x00
+.DATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b10010010
+    .byte 0b00000000
+    .byte 0x00
+.UCODE:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11111010
+    .byte 0b10101111
+    .byte 0x00
+.UDATA:
+    .word 0x0000
+    .word 0x0000
+    .byte 0x00
+    .byte 0b11110010
+    .byte 0b00000000
+    .byte 0x00
+.TSS:
+    .quad 0x00
+    .quad 0x00
+
+    .globl g_GDTR
+g_GDTR:
+    .word g_GDTR - g_GDT
+    .quad g_GDT

usr/src/sp1/head/amd64/gdt.h

@@ -0,0 +1,27 @@
+/*
+ * Copyright (c) 2026, Mirocom Laboratories
+ * All rights reserved.
+ *
+ * The following sources are CONFIDENTIAL and PROPRIETARY
+ * property of Mirocom Laboratories. Unauthorized copying,
+ * use, distribution or modification of this file, in whole
+ * and in part, is strictly prohibited without the prior written
+ * consent from Mirocom Laboratories.
+ */
+
+#ifndef _MACHINE_GDT_H_
+#define _MACHINE_GDT_H_ 1
+
+/* Kernel code/data */
+#define GDT_KCODE  0x08
+#define GDT_KDATA  0x10
+
+/* User code/data */
+#define GDT_UCODE  0x18
+#define GDT_UDATA  0x20
+
+/* Task state segment */
+#define GDT_TSS    0x28
+#define GDT_TSS_INDEX 0x05
+
+#endif  /* !_MACHINE_GDT_H_ */