Search code examples
assemblyx86intelgdt

How to update Data Segment Selector in Protected mode

I want to update Data Segment selector to point to some other entry in GDT. But Since I am very new to assembly, I can not do it in my code. However I have updated the Code Segment Selector by using following assembly instruction:

ljmp $(GDT_TABLE_INDEX), $(1f)     //This instruction simply points code segment to some other entry in GDT and move to next label.

Is there some similar or alternative instruction to update Data Segment Selector also ?

Solution

  • You can change the data segment selector using the mov instruction. For example, if you want to set ds to 0x1234, use:

    mov $1234, %ax
mov %ax, %ds

    Note that there is no mov imm, sreg instruction, so you first have to move the selector's number into a general purpose register. You might also find it convenient to pop into a segment register:

    push $1234
pop %ds