Ned some help with the GDT

[Pyrofan1]

I understand what the GDT is for, but I'm not exactly sure how to create one.
I've come up with this code
gdt.h

Code: Select all

extern unsigned char gdt[4]

void fill_gdt(void)
{
	unsigned char gdt[4];
	gdt[0]=0x00;
	gdt[1]=0x9A;
	gdt[2]=0x92;
	gdt[3]=0x00;
}

extern void _list_gdt(void);

gdt.s

Code: Select all

.global _list_gdt
.global gdt

.type _list_gdt,@function
_list_gdt:
	lgdt $(gdt)
	ret

But i'm almost %100 sure that this code won't work. How can I fix it?

[Combuster]

the gdt is an array of descriptors. each gdt descriptor is 8 bytes, and you need at least three: null, code and data.

For the exact format, refer to the intel manuals

[JAAman]

yes, this is exactly where the intel manuals are invaluable -- become very familier with them (the information you need is in 3A:3.4.5, the associated diagram shows the GDT entries very clearly, as 2 32bit fields)

[xyjamepa]

Hi...
try this it might helphttp://osdever.net/bkerndev/Docs/intro.htm