Strange bugs in paging and bitsets in kernel

[kfreezen]

My kernel has a very strange bug. Somehow, my kernel is triple faulting in the bitset implementation's code.

Nine times out of ten it will triple fault. The bit that is my kernel is attempting to set when it triple faults seems entirely random.
However, the range seems fairly consistent. 0x1FFFFA0-0x1FFFFFF

Another weird issue that probably has a very easy fix is happening (that i think mite be related to this issue). For example, the bit storage will be at 0x106000.
Here's the particular function that's causing the error. (I think)

Code: Select all

int SetBits(Bitset* b, int bit_start, int bit_end) {
	kprintf("bit_start=%x, bit_end=%x\n", bit_start, bit_end);
	wait(1);
	register int i;
	if(bit_start == 0) {
		b->bits_before_bit_change = bit_end;
		b->bits_type = on;
	} else if(bit_start == b->bits_before_bit_change && b->bits_type==on) {
		b->bits_before_bit_change = bit_end;
		b->bits_type = on;
	}
	
	/*if((bit_start%32)==0 && (bit_end%32)==0) {
		int iend = bit_end/32;
		for(i = bit_start/32; i<iend; i++) {
			if((i%0x5000)==0) {
				kprintf("loop!%x\n", i*32);
			}
			if(i >= b->length) {
				kprintf("YOU FAILED!!\n");
				return 1;
			}
			b->bit_storage[i] = 0xFFFFFFFF;
		}
		return 0;
	}*/
	
	for(i = bit_start; i<bit_end; i++) {
		if((i%32)==0 && bit_end-i>=32) { /*
			if(i/32 >= b->length) {
				return 1;
			} else {
				// Mark it. duh.
				b->bit_storage[i/32] = 0xFFFFFFFF;
				i+=31;
			}*/
		} else if(SetBit(b, i) == 1) {
			return 1;
		}
		if((UInt32) i>=0x1ffffa0) {
			PutHex(i);
			PrintChar('\r');
		}
	}
	
	return 0;
}

the kprintf()'s, wait()'s and Put*()'s are merely there for debugging.

also, paging code (which is calling the SetBits() function)

Code: Select all

Bitset* bits;
...
#define ONE_TO_ONE_MAP_MB 32
...
void Paging_Init(int kb_of_mem) {
...
        for(i=0; i<(ONE_TO_ONE_MAP_MB/4); i++) {
		kprintf("start=");
		if(SetBits(bits, (i*MEGABYTE*4), ((i+1)*MEGABYTE*4))==1) {
			kprintf("Error");
		}
		kprintf("middle=");
		PageTable* pt = IdMapPageTable(i);
		
		pd->d[i] = AssemblePDE((Pointer) pt->t, 0x7);
		kprintf("%x %x, %x\n", i, (i*MEGABYTE*4), ((i+1)*MEGABYTE*4));
	}
...
}

Anyway, any help would be greatly appreciated.

[Combuster]

Always post bochs logs on a crash.

[kfreezen]

I'm sorry. It is qemu and AFAIK it does not have that capability. Anyway, I believe I resolved the issue. The problem was that I was not allocating memory of the proper size for the bitset. anyway can anyone explain how 0x106000+0xb00000 = 0x3000000? (It will probably be another simple fix so don't bother answering unless you really want to.)

EDIT: Found a workaround for the above issue of 0x106000+0xb00000 = 0x3000000. It may have been due to adding a UInt32 pointer to a UInt32.

May others not show the same ignorance I have perceived myself to have shown