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/*
* bubbl
* Copyright (C) 2025 Raghuram Subramani <raghus2247@gmail.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
/* Bitmap Based Allocation:
* https://web.archive.org/web/20190316115948/http://www.brokenthorn.com/Resources/OSDev17.html
*/
/* TODO: Stack based allocation? */
#include <kernel/halt.h>
#include <kernel/spinlock.h>
#include <libk/stdio.h>
#include <mm/memory_map.h>
#include <mm/physical_mm.h>
#include <stdbool.h>
#include <stdint.h>
namespace PhysicalMM
{
extern "C" uint32_t kernel_start;
extern "C" uint32_t kernel_end;
uint32_t l_block_count = 0;
uint32_t l_total_free_blocks = 0;
uint32_t l_memory_map[MAX_BLOCKS / BITMAP_ENTRY_SIZE];
Spinlock l_lock;
ALWAYS_INLINE static void
log_memory_map(free_memory_regions_t *free_memory_regions)
{
printk("\nphysical_mm", "Free Memory Regions:");
for (int i = 0; i < free_memory_regions->n_regions; i++)
printk("physical_mm",
"start: 0x%.08x | length: 0x%.08x",
free_memory_regions->region_list[i]->addr_low,
free_memory_regions->region_list[i]->len_low);
printk("\nphysical_mm", "Kernel region:");
printk("physical_mm", "Start: 0x%x", &kernel_start);
printk("physical_mm", "End: 0x%x", &kernel_end);
printk("physical_mm",
"Size: 0x%x",
((uint32_t) &kernel_end) - ((uint32_t) &kernel_start));
}
ALWAYS_INLINE static void
initialize_region(uint32_t start, uint32_t length)
{
/* Get the location of the start address in the bitmap */
uint32_t bit = start / BLOCK_SIZE;
uint32_t n_blocks = length / BLOCK_SIZE;
for (; n_blocks > 0; n_blocks--)
if (test_bit(bit, l_memory_map))
set_usable(bit++, &l_total_free_blocks, l_memory_map);
/* First block is always used (first 64KiB) */
if (!test_bit(0, l_memory_map))
set_used(0, &l_total_free_blocks, l_memory_map);
}
ALWAYS_INLINE static void
deinitialize_region(uint32_t start, uint32_t length)
{
uint32_t bit = start / BLOCK_SIZE;
uint32_t n_blocks = length / BLOCK_SIZE;
if (length % BLOCK_SIZE > 0)
n_blocks++;
for (; n_blocks > 0; n_blocks--)
set_used(bit++, &l_total_free_blocks, l_memory_map);
}
ALWAYS_INLINE static uint32_t
find_free_block(void)
{
/* TODO: Why doesn't using block_count instead of MAX_BLOCKS work? */
for (uint32_t i = 0; i < MAX_BLOCKS / BITMAP_ENTRY_SIZE; i++)
/* At least one block in the entry isn't in use */
if (l_memory_map[i] != 0xffffffff)
/* Test each bit to see if it's zero */
for (uint32_t j = 0; j < BITMAP_ENTRY_SIZE; j++)
if (!test_bit(i * BITMAP_ENTRY_SIZE + j, l_memory_map))
return i * BITMAP_ENTRY_SIZE + j;
/* Shouldn't be reached, since we're keeping track of the number of free
* blocks */
ASSERT_NOT_REACHED();
return -1;
}
void
initialize(void)
{
free_memory_regions_t *free_memory_regions = MemoryMap::get_free_regions();
log_memory_map(free_memory_regions);
l_lock.acquire();
/* All blocks are initially used */
/* TODO: Move this block to a place after block_count is set. This is why
* using block_count instead of MAX_BLOCKS wasn't working. */
for (uint32_t i = 0; i < MAX_BLOCKS / BITMAP_ENTRY_SIZE; i++)
l_memory_map[i] = 0xffffffff;
for (int i = 0; i < free_memory_regions->n_regions; i++) {
multiboot_memory_map_t *region = free_memory_regions->region_list[i];
initialize_region(region->addr_low, region->len_low);
}
uint32_t kernel_size = ((uint32_t) &kernel_end) - ((uint32_t) &kernel_start);
deinitialize_region((uint32_t) &kernel_start, kernel_size);
/* Deinitialize first 8MiB */
deinitialize_region(0, 8 * MiB);
l_lock.release();
/* Manually loop through and calculate the number of free blocks. */
for (uint32_t i = 0; i < MAX_BLOCKS / BITMAP_ENTRY_SIZE; i++)
/* At least one block in the entry isn't in use */
if (l_memory_map[i] != 0xffffffff)
/* Test each bit to see if it's zero */
for (uint32_t j = 0; j < BITMAP_ENTRY_SIZE; j++)
if (!test_bit(i * BITMAP_ENTRY_SIZE + j, l_memory_map))
l_total_free_blocks++;
printk("physical_mm", "Total free blocks: 0x%x", l_total_free_blocks);
}
void *
allocate_block(void)
{
if (l_total_free_blocks == 0) {
printk("physical_mm", "No more free blocks!");
return NULL;
}
l_lock.acquire();
uint32_t block = find_free_block();
set_used(block, &l_total_free_blocks, l_memory_map);
l_lock.release();
uint32_t physical_address = block * BLOCK_SIZE;
return (void *) physical_address;
}
void
free_block(void *physical_address)
{
uint32_t block = ((uint32_t) physical_address) / BLOCK_SIZE;
set_usable(block, &l_total_free_blocks, l_memory_map);
}
}
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