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#ifdef x86

#include <Segmentation.hpp>
#include <Interrupt.hpp>
#include <Registration.hpp>

extern "C" void FlushTSS();

/* Don't compile Native.asm on non-x86 */
extern "C" {
	struct NativeDescTablePointer GDTPtr;
	struct SegmentDescriptor GDTable[6];
	struct TSS systemTSS;
}

extern "C" void setGate(uint32_t gateNo, uint32_t base, uint32_t limit, uint8_t access, uint8_t granularity) {
	GDTable[gateNo].lowerBase = base & 0xffff;
	GDTable[gateNo].middleBase = (base >> 16) & 0xff;
	GDTable[gateNo].higherBase = (base >> 24) & 0xff;

	GDTable[gateNo].lowerLimit = limit & 0xffff;
	GDTable[gateNo].granularity = (limit >> 16) & 0xf;

	GDTable[gateNo].granularity |= granularity & 0xf0;
	GDTable[gateNo].access = access;
}

extern "C" void setupTSS(uint32_t offset, uint16_t ss0, uint16_t esp0) {
	uint32_t base = (uint32_t) &systemTSS;
	uint32_t size = base + sizeof(TSS);
		
	setGate(offset, base, size, 0xe9, 1);

	unsigned char *tssLocation = (unsigned char*) &systemTSS;
	for(int offset = 0; offset < sizeof(systemTSS); offset++) {
		tssLocation[offset] = 0;
	}

//	systemTSS.eflags = 0x1202;

	systemTSS.ss0 = ss0;
	systemTSS.esp0 = esp0;

	systemTSS.cs = 0x0B;
	systemTSS.ss = // These specify what segments 
	systemTSS.ds = // should be loaded when the 
	systemTSS.es = // processor switches to 
	systemTSS.fs = // kernel mode.
	systemTSS.gs =
	0x13;

	systemTSS.iomap = sizeof(TSS);
}

extern "C" void setupSegmentation() {
	#ifdef segmentationEnabled
		GDTPtr.limit = (sizeof(struct SegmentDescriptor) * 3) - 1;
		GDTPtr.base = (uint32_t) GDTable;

		setGate(0, 0, 0, 0, 0); // NULL Descriptor
		setGate(1, 0, 0xffffffff, 0x9a, 0xcf);
		setGate(2, 0, 0xffffffff, 0x92, 0xcf);
		setGate(3, 0, 0xffffffff, 0xfa, 0xcf);
		setGate(4, 0, 0xffffffff, 0xf2, 0xcf);
		setupTSS(5, 0x10, 0x0); // fine without FlushTSS

		FlushGDT();
		FlushTSS(); // This is a problem - { mov ax, 0x2b; ltr ax; ret }
	#endif
}

Code: Select all

extern GDTPtr

	FlushGDT:
		lgdt [GDTPtr]
		mov ax, 0x10
		mov ds, ax
		mov es, ax
		mov fs, ax
		mov gs, ax
		mov ss, ax
		jmp 0x08:SegmentReturn
	SegmentReturn:
		ret

	FlushTSS:
		mov ax, 0x2B
		ltr ax
		ret

Code: Select all

/* 'Global Descriptor Table' - Task State Segment */
	struct TSS
	{
		uint32_t prev_tss;
		uint32_t esp0;       
		uint32_t ss0;
		uint32_t esp1; 
		uint32_t ss1;
		uint32_t esp2;
		uint32_t ss2;
		uint32_t cr3;
		uint32_t eip;
		uint32_t eflags;
		uint32_t eax;
		uint32_t ecx;
		uint32_t edx;
		uint32_t ebx;
		uint32_t esp;
		uint32_t ebp;
		uint32_t esi;
		uint32_t edi;
		uint32_t es;         
		uint32_t cs;        
		uint32_t ss;        
		uint32_t ds;        
		uint32_t fs;       
		uint32_t gs;         
		uint32_t ldt;      
		uint16_t trap;
		uint16_t iomap;
	} __attribute__((__packed__));
	typedef TSS TaskSegment;

	/* 'Global Descriptor Table' - Segment Descriptor */
	struct SegmentDescriptor {
		unsigned short lowerLimit;
		unsigned short lowerBase;
		unsigned char middleBase;
		unsigned char access;
		unsigned char granularity;
		unsigned char higherBase;
	} __attribute__((packed));