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Posted: **Thu Mar 03, 2016 11:43 pm**

Hey all.
Im writing a basic allocator for my kernel.
I made a awesome allocate function that works great.
I use linked structs that contain infomation about free space for my allocator, here is the struct:

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typedef struct
{
	void* next;
	void* prev;
	uint32_t size;
	void* base;
} free_loc;

That all works fine, but I want to be able to load free memory areas into seperate free_loc's.
I am using grub to get the memory map. Here is my memory allocator init function:

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void pmm_init(void* mmloc, unsigned long mmsize)
{
	mmap_entry_t* cmap=(mmap_entry_t*)mmloc;
	
	int i=0;
	free_loc* last;
	while(cmap < (mmap_entry_t*) mmloc + mmsize)
	{
		if(cmap->type == 1)
		{
			if(i==0)
			{
				first->size = cmap->len;
				first->base = cmap->base;
				first->prev = 0;
				last = first;
			}else{
				free_loc* append;
				append->size = cmap->len;
				append->base = cmap->base;
				append->prev = last;
				last->next = append;
				last = append;
			}
			i++;
		}
		cmap = (mmap_entry_t*) ( (unsigned int)cmap + cmap->size + sizeof(uint32_t));
	}
}

It loops through the memory map, checking if a area is useable.
Heres the issue: I need to somehow leave a reference to the last area for the next area to attach its 'prev' too.
I am trying to use the pointer 'last' to acheive this.
It does what it needs to do fine, but it modifies the last area at this line:

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last = append;

I basicly want to change the 'free_loc' the pointer points too, but it is overwriting the data instead.
Im terrible at explaining so hopefully you can understand.

Thanks, Harry

Posted: **Thu Mar 03, 2016 11:45 pm**

OK, I actually solved this 5 seconds after I hit submit, all I had to do was change

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last = append;

to

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last = (void*)append;

. C probaly recignizes that were passing a location rather a value.

Yay! A working allocator

OSDev.org

[SOLVED] Stuck on passing grub memory map into my allocator

[SOLVED] Stuck on passing grub memory map into my allocator

Re: Stuck on passing grub memory map into my allocator