Untitled_Kernel/src/physmem.c

#include "physmem.h"
#include <stdint.h>
#include <io.h>

uint8_t* pmem_bitmap;


unsigned int build_bitmap(mb_mmap_entry_t* mmap, int mmap_size) {
    unsigned int pages_allocated = 0;    
    //Set up a bitmap and set it all to 1
    pmem_bitmap = &_kernel_end;
    uint32_t bitmap_end = (uint32_t)pmem_bitmap + (MEM_MAX / (PAGE_SIZE*8));
    printf(default_output, "bitmap at: %X", pmem_bitmap);
    for(unsigned int i = 0; i < bitmap_end; i++) {
        *(pmem_bitmap + i) = 0xFF;
    }

    int mmap_end = (uint32_t)mmap + mmap_size;
    for(;
        (int)mmap < mmap_end;
        mmap = (mb_mmap_entry_t*)((int)mmap + mmap->entry_size + sizeof(mmap->entry_size))) {


        printf(default_output,"__MMAP_ENTRY__:\nSTART_ADDR:%X\nSIZE:%X\nTYPE:%u\n",(uint32_t)mmap->addr, (uint32_t)mmap->mem_size, mmap->type);


        uint8_t* mem_bottom =(uint8_t*) (((uint32_t)mmap->addr + PAGE_SIZE - 1) & ~(PAGE_SIZE - 1));

        if(mmap->type != 1) {
            //nah...
            continue;
        }
    
        //round the starting address of the map to the nearest page boundary so we don't mark half used pages as free
        uint8_t* mem_top = (uint8_t*) (((uint32_t)mmap->addr + (uint32_t)mmap->mem_size) & ~(PAGE_SIZE - 1));


        printf(default_output, "lowerpage:%X|upper:%X\n", mem_bottom, mem_top);
        
        //ok lets set the bitmap
        /* bullshit dont use it
        for(uint8_t* i = mem_bottom; i < mem_top; i+=4096) {
           
            //Watch out for cutting up kernelspace
            if((unsigned int)mem_bottom + (unsigned int)i < bitmap_end)
                continue;
            
            //ok we can just say this whole chunk is available
            *(pmem_bitmap + (unsigned int)i) = 0; 
        }
        */
        int page_count = (mem_top - mem_bottom) / PAGE_SIZE;
        for(int i = 0; i < page_count; i++){
            
            //OK which page is this
            uint8_t* page_addr = mem_bottom + (PAGE_SIZE * i);
            
            if((uint32_t)page_addr < bitmap_end) { 
                //bruh this is in lowmem or the kernel
                continue;
            }
            
            //Available. Calculate the offset of the bit on the bitmap based on the page address
            unsigned int pagenumber = (unsigned int)page_addr / PAGE_SIZE;
            uint8_t* bitmap_byte = pmem_bitmap + (pagenumber / 8); 
            int bitmap_bit = pagenumber % 8;

            //ok now set the bit to unused
            *bitmap_byte &= ~(0x80 >> bitmap_bit);
            pages_allocated++;
        }
        
    } 
   
    return pages_allocated;
    
}