Add an example user space process

src/bootloader.asm

@@ -224,30 +224,30 @@ jmp load_gdt
 
 gdt_start:
 gdt_0: dq 0x0000000000000000
-gdt_1:
+gdt_32_code:
 .limit_low:     dw 0xFFFF
 .base_low:      dw 0x0000
 .base_middle:   db 0x00
 .access:        db 10011010b ; present, ring 0, code, executable, readable
 .flags:         db 11001111b ; 32-bit, 4KB granularity
 .base_high:     db 0x00
-gdt_1_end:
-gdt_2:
+gdt_32_code_end:
+gdt_64_code:
 .limit_low:     dw 0xFFFF
 .base_low:      dw 0x0000
 .base_middle:   db 0x00
-.access:        db 10011010b ;  present, ring 0, code, executable, readable
+.access:        db 10011010b ; present, ring 0, code, executable, readable
 .flags:         db 10101111b ; long mode (L bit)
 .base_high:     db 0x00
-gdt_2_end:
-gdt_3:
+gdt_64_code_end:
+gdt_data:
 .limit_low:     dw 0xFFFF
 .base_low:      dw 0x0000
 .base_middle:   db 0x00
 .access:        db 10010010b ; present, ring 0, data, writable
 .flags:         db 00000000b
 .base_high:     db 0x00
-gdt_3_end:
+gdt_data_end:
 gdt_end:
 
 gdt_descriptor:
@@ -276,23 +276,30 @@ protected_mode:
     mov ss, ax
     mov esp, 0x00090000
 
-    ; zero page table memory at 0x00010000 (3 pages = 768 dwords)
+    ; zero page table memory
     mov edi, 0x00010000
-    mov ecx, 768
+    mov ecx, 256 * 5
     xor eax, eax
     rep stosd
 
     ; PML4[0] -> PDPT at 0x00011000
     mov dword [0x00010000], 0x00011003
-    ; PDPT[0] -> PD at 0x00012000
-    mov dword [0x00011000], 0x00012003
+    ; PML4[511] -> PDPT at 0x00012000
+    mov dword [0x00010FF8], 0x00012003
+    ; PML4[0].PDPT[0] -> PD at 0x00013000
+    mov dword [0x00011000], 0x00013003
+    ; PML4[511].PDPT[510] -> PD at 0x00014000
+    mov dword [0x00012FF0], 0x00014003
     ; PD: fill 64 entries, each mapping 2MB
-    mov edi, 0x00012000
+    mov edi, 0x00013000
     mov eax, 0x00000083   ; present, writable, huge page, base 0
     mov ecx, 64
 
 .fill_pd:
+    mov ebx, edi
+    add ebx, 0x1000
     mov dword [edi], eax
+    mov dword [ebx], eax
     add edi, 8
     add eax, 0x00200000   ; next 2MB
     loop .fill_pd
@@ -327,11 +334,11 @@ long_mode:
     mov ds, ax
     mov es, ax
     mov ss, ax
-    mov rsp, 0x0000000000090000
+    mov rsp, 0xFFFFFFFF80090000
 
     xor rax, rax
     xor rbx, rbx
     xor rcx, rcx
     xor rdx, rdx
 
-    jmp 0x00020000
+    jmp 0xFFFFFFFF80020000