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Posted: **Sat Mar 03, 2012 12:01 pm**

Hello,

I am trying to install a TSS into the GDT. The processor triple faults on the _asm ltr eax; instruction though. Here is the code (it handles both my GDT and TSS).

Code: Select all

void GDT::InstallGDT()
{
	GDT::Private::GDTList = (GDT::Private::GDTStr*)Heap::Malloc(8 * 256, 0);
	memset(GDT::Private::GDTList, 0, 8 * 256);

	GDT::InitializeKernelGDT();

	GDT::Private::GDTItr itr;
	itr.Size = (8 * 256) - 1;
	itr.Offset = (dword)GDT::Private::GDTList;
	_asm lgdt [itr];

	_asm cli;

	_asm mov eax, 0x2B;
	_asm ltr eax;

	_asm sti;
}

void GDT::InitializeKernelGDT()
{
	GDT::InstallGDTEntry(0xFFFFF, 0, 1, 1, 0, 1, 1, 1);
	GDT::InstallGDTEntry(0xFFFFF, 0, 1, 0, 0, 1, 1, 2);
	GDT::InstallGDTEntry(0xFFFFF, 0, 1, 1, 3, 1, 1, 3);
	GDT::InstallGDTEntry(0xFFFFF, 0, 1, 0, 3, 1, 1, 4);

	GDT::InstallGDTEntry((dword)&GDT::Private::KTSS + sizeof(GDT::Private::TSS), (dword)&GDT::Private::KTSS, false, true, 3, true, false, 5);
	memset((void*)&GDT::Private::KTSS, 0, sizeof(GDT::Private::TSS));

	GDT::Private::KTSS.ss0 = 0x10;
	GDT::Private::KTSS.esp0 = 0;

	GDT::Private::KTSS.cs = 0xB;
	GDT::Private::KTSS.ss = 0x13;
	GDT::Private::KTSS.es = 0x13;
	GDT::Private::KTSS.ds = 0x13;
	GDT::Private::KTSS.fs = 0x13;
	GDT::Private::KTSS.gs = 0x13;
}

void GDT::InstallGDTEntry(dword Limit, dword Base, bool ReadandWrite, bool Code, byte Privl, bool i32Bit, bool i4kbGran, byte Index)
{
	GDT::Private::GDTStr newGdt;

	newGdt.Limit = (Limit & 0xFFFF);
	newGdt.Base = (Base & 0xFFFF);
	newGdt.Base2 = ((Base >> 16) & 0xFF);

	newGdt.Accessed = 1;
	newGdt.ReadWrite = ReadandWrite;
	newGdt.Direction = 0;
	newGdt.Executable = Code;
	newGdt.Reserved1 = 1;
	newGdt.Privl = Privl;
	newGdt.Present = 1;

	newGdt.Limit2 = ((Limit >> 16) & 0xF);

	newGdt.Reserved2 = 0;
	newGdt.Reserved3 = 0;
	newGdt.Size = i32Bit;
	newGdt.Gran = i4kbGran;

	newGdt.Base3 = ((Base >> 24) & 0xF);

	memcpy(&GDT::Private::GDTList[Index], &newGdt, sizeof(GDT::Private::GDTStr));
}

Posted: **Sat Mar 03, 2012 12:23 pm**

According to this:

Protected Mode Exceptions wrote:#GP(0) for an illegal memory operand effective address in the CS, DS, ES, FS, or GS segments; #SS(0) for an illegal address in the SS segment; #GP(0) if the current privilege level is not 0; #GP(selector) if the object named by the source selector is not a TSS or is already busy; #NP(selector) if the TSS is marked "not present"; #PF(fault-code) for a page fault.

Which one is it?

Posted: **Sat Mar 03, 2012 12:27 pm**

Thank you for the reply. I solved the problem, a few incorrect variables.

Hoozim

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