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#include <stdint.h>
#include "panic.h"
#include "pmap.h"
#define PAGEMAP_START (0x00040000)
#define PAGEMAP_END (0x00060000)
#define PAGE_USED(n) ((*(uint8_t *)(PAGEMAP_START + (n >> 3)) >> (n & 7)) & 1)
#define CLEAR_PAGE(n) *(uint8_t *)(PAGEMAP_START + (n >> 3)) &= ~(1 << (n & 7))
#define SET_PAGE(n) *(uint8_t *)(PAGEMAP_START + (n >> 3)) |= 1 << (n & 7)
#define KBSS_START (0x04000000)
#define USER_START (0x08000000)
extern const void _kernel_bss_end;
uint32_t kernel_pages_left;
uint32_t user_pages_left;
uint32_t max_kernel_pages;
uint32_t max_user_pages;
enum {
BMET_FREE = 1
};
enum {
BMEF_NON_VOLATILE = 0x02
};
struct bios_mmap_entry {
uint64_t base;
uint64_t length;
uint32_t type;
uint32_t flags;
};
void init_pagemap() {
for (uint32_t *i = (uint32_t *)(PAGEMAP_START + (KBSS_START >> 15)); i < (uint32_t *)PAGEMAP_END; ++i)
*i = 0xffffffff;
const struct bios_mmap_entry *mmap_p = (const struct bios_mmap_entry *)0x00010000;
const struct bios_mmap_entry *mmap_e = (const struct bios_mmap_entry *)(0x00010000 + *(uint16_t *)0x00004006);
for (; mmap_p < mmap_e; ++mmap_p) {
if (mmap_p->type != BMET_FREE)
continue;
if (mmap_p->base > 0xffffffff)
continue;
uint32_t base_page = ((mmap_p->base - 1) >> 12) + 1;
uint64_t end = mmap_p->base + mmap_p->length;
if (end > 0xffffffff)
end = 0x100000000;
uint32_t end_page = end >> 12;
for (uint32_t i = base_page; i < end_page; ++i)
CLEAR_PAGE(i);
}
uint32_t kernel_pages = (((uint32_t)&_kernel_bss_end - 1) >> 12) + 1;
for (uint32_t i = 0; i < kernel_pages; ++i)
SET_PAGE(i);
kernel_pages_left = 0;
for (uint32_t i = KBSS_START >> 12; i < USER_START >> 12; ++i)
if (!PAGE_USED(i))
++kernel_pages_left;
max_kernel_pages = kernel_pages_left;
user_pages_left = 0;
for (uint32_t i = USER_START >> 12; i < 1048576; ++i)
if (!PAGE_USED(i))
++user_pages_left;
max_user_pages = user_pages_left;
}
//very inneficient algorithm, just returns first hole big enough.
//a smarter algorithm might pick the smallest one available,
//and go by bytes (or dwords) instead of bits where possible.
void *allocate_kernel_pages(uint32_t n) {
uint32_t run = 0;
for (uint32_t page = KBSS_START >> 12; page < USER_START >> 12; ++page) {
if (PAGE_USED(page))
run = 0;
else if (++run == n) {
uint32_t start = page - run + 1;
for (uint32_t i = start; i <= page; ++i)
SET_PAGE(i);
kernel_pages_left -= n;
return (void *)(start << 12);
}
}
return 0;
}
//very inneficient algorithm, just returns first hole big enough.
//a smarter algorithm might pick the smallest one available,
//and go by bytes (or dwords) instead of bits where possible.
void *allocate_user_pages(uint32_t n) {
uint32_t run = 0;
for (uint32_t page = USER_START >> 12; page < 1048576; ++page) {
if (PAGE_USED(page))
run = 0;
else if (++run == n) {
uint32_t start = page - run + 1;
for (uint32_t i = start; i <= page; ++i)
SET_PAGE(i);
user_pages_left -= n;
return (void *)(start << 12);
}
}
return 0;
}
//in the future, change this to go by bytes or dwords instead of bits.
void free_pages(const void *ptr, uint32_t n) {
uint32_t page = (uint32_t)ptr >> 12;
for (uint32_t i = page; i < page + n; ++i)
CLEAR_PAGE(i);
if ((uint32_t)ptr >= USER_START)
user_pages_left += n;
else
kernel_pages_left += n;
}
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