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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 <stdbool.h>
#include <stdint.h>
#include <libk/stdio.h>
#include <mm/memory_map.h>
#include <mm/physical_mm.h>
#include <kernel/halt.h>
extern uint32_t kernel_start;
extern uint32_t kernel_end;
uint32_t block_count = 0;
uint32_t total_free_blocks = 0;
uint32_t memory_map[MAX_BLOCKS / BITMAP_ENTRY_SIZE];
ALWAYS_INLINE static void
physical_mm_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
physical_mm_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 (physical_mm_test_bit(bit, memory_map))
physical_mm_set_usable(bit++, &total_free_blocks, memory_map);
/* First block is always used (first 64 KiB) */
if (!physical_mm_test_bit(0, memory_map))
physical_mm_set_used(0, &total_free_blocks, memory_map);
}
ALWAYS_INLINE static void
physical_mm_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--)
if (!physical_mm_test_bit(bit, memory_map))
physical_mm_set_used(bit++, &total_free_blocks, memory_map);
}
void
physical_mm_init(void)
{
free_memory_regions_t *free_memory_regions = memory_map_get_free_regions();
physical_mm_log_memory_map(free_memory_regions);
/* 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++)
memory_map[i] = 0xffffffff;
uint32_t total_free_memory = 0;
for (int i = 0; i < free_memory_regions->n_regions; i++) {
multiboot_memory_map_t *region = free_memory_regions->region_list[i];
total_free_memory += region->len_low;
physical_mm_initialize_region(region->addr_low, region->len_low);
}
uint32_t kernel_size = ((uint32_t) &kernel_end) - ((uint32_t) &kernel_start);
physical_mm_deinitialize_region((uint32_t) &kernel_start, kernel_size);
total_free_memory -= kernel_size;
block_count = total_free_memory / BLOCK_SIZE;
printk("\nphysical_mm", "Total blocks: 0x%x", block_count);
printk("physical_mm", "Total free blocks: 0x%x", total_free_blocks);
#if 0
/* Manually loop through and calculate the number of free blocks. */
uint32_t free_blcks = 0;
for (uint32_t i = 0; i < MAX_BLOCKS / BITMAP_ENTRY_SIZE; i++)
/* At least one block in the entry isn't in use */
if (memory_map[i] != 0xffffffff)
/* Test each bit to see if it's zero */
for (uint32_t j = 0; j < BITMAP_ENTRY_SIZE; j++)
if (!physical_mm_test_bit(i * BITMAP_ENTRY_SIZE + j, memory_map))
free_blcks++;
printk("physical_mm",
"Experimentally calculated free blocks: 0x%x",
free_blcks);
#endif
}
uint32_t
physical_mm_find_first_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 (memory_map[i] != 0xffffffff)
/* Test each bit to see if it's zero */
for (uint32_t j = 0; j < BITMAP_ENTRY_SIZE; j++)
if (!physical_mm_test_bit(i * BITMAP_ENTRY_SIZE + j, 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 *
physical_mm_allocate_block(void)
{
if (total_free_blocks == 0) {
printk("physical_mm", "No more free blocks!");
return NULL;
}
uint32_t block = physical_mm_find_first_free_block();
physical_mm_set_used(block, &total_free_blocks, memory_map);
uint32_t physical_address = block * BLOCK_SIZE;
return (void *) physical_address;
}
void
physical_mm_free_block(void *physical_address)
{
uint32_t block = ((uint32_t) physical_address) / BLOCK_SIZE;
physical_mm_set_usable(block, &total_free_blocks, memory_map);
}
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