changing the GDT fails when hardware virtualization is enabled

[andrej1991]

Hello,
I'm writing an own os and when I try to change the GDT it fires IRQ 6 (invalid opcode). When the hardware virtualization is disabled everything is fine.
The code which supposed to change the GDT:

Code: Select all

    call    get_gdt_base
    lea     GDTdescriptor, %ebx
    movl    %eax, %ds:2(%ebx)
    lea     memory_descriptor, %eax
    sgdt    (oldGDTdescriptor)
    push    %eax
    call    create_base_gdt
    movw    $8, %dx
    mulw    %dx
    decw    %ax
    movw    %ax, %ds:(%ebx)
    lgdt    (GDTdescriptor)
    movl    $0x10,%eax
    mov     %ax,%ds
    mov     %ax,%es
    mov     %ax,%fs
    mov     %ax,%gs
    mov     %ax,%ss
    jmp     $8,$next
    next:
    movl    $0x3FFE0, %eax
    movl    %eax, %esp
    call    main

Function "get_gdt_base" just select a valid area in the memory where the GDT can fit.
Function "create_base_gdt" creates a GDT with the following entries:

Code: Select all

.quad 0x0
.quad 0x00C09B0000008000 /*code segment*/
.quad 0x00C0930000008000 /*data segment*/

I'm using VirtualBox 5.1.2 r108956 for ubuntu 14.04.

Thank you in advance,
Andrej

[socratis]

I believe that your question is pretty specialized. You may have a better chance of getting it answered if you ask the developers either at the mailing list or on IRC. See https://www.virtualbox.org/wiki/Community for details.