fireOS/malloc.c at master · Firewiz/fireOS · GitHub

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#include "malloc.h"
#include "paging.h"

unsigned char *malloc_arena = (unsigned char *)0x800000;

void *malloc(unsigned int size) {
  struct malloc_header *headptr = (struct malloc_header *) malloc_arena;
  while(1) {
    if(!is_present((int) headptr / 0x1000)) {
      nonidentity_page((int) headptr / 0x1000);
    }
    if(!(headptr->flags & FLAG_ALLOCATED) || headptr->magic != MALLOC_MAGIC) { /* end of arena */
      headptr->flags = FLAG_ALLOCATED | FLAG_INUSE;
      headptr->length = size;
      unsigned int i;
      for(i = 0; i < size; i+=4096) {
	if(!is_present(i + ((int) headptr / 0x1000))) {
	  nonidentity_page(i + ((int) headptr / 0x1000));
	}
      }
      return headptr + 1;
    } else if(!(headptr->flags & FLAG_INUSE)) { /* possible fit */
      if(headptr->length >= size) {	 /* definite fit */
	// check to see if we need to alloc another header
	if((headptr->length - 1) > size) { /* ok to alloc a new header */
	  struct malloc_header *newhead = headptr + (size + sizeof(struct malloc_header)) / sizeof(struct malloc_header);
	  newhead->length = headptr->length - size - sizeof(struct malloc_header);
	  newhead->flags = FLAG_ALLOCATED;
	  newhead->magic = MALLOC_MAGIC;
	  headptr->length = size;
	}
	headptr->flags |= FLAG_INUSE;
	unsigned int i;
	for(i = 0; i < size; i+=4096) {
	  if(!is_present(i + ((int) headptr / 0x1000))) {
	    nonidentity_page(i + ((int) headptr / 0x1000));
	  }
	}
	return headptr + 1;
      } else {
	headptr += headptr->length / sizeof(struct malloc_header);
	headptr += 1;
      }
    } else {			/* next headptr */
      headptr += headptr->length / sizeof(struct malloc_header);
      headptr += 1;
    }
  }
}

void free(void *p) {
  struct malloc_header *headptr = p - sizeof(struct malloc_header);
  struct malloc_header *nexthead = p + headptr->length;
  if(!(nexthead->flags & FLAG_ALLOCATED)) { /* this block is at the end of the arena */
    headptr->flags = 0;
  } else if(!(nexthead->flags & FLAG_INUSE)) { /* join free blocks */
    headptr->length += nexthead->length + sizeof(struct malloc_header);
    nexthead->flags = 0;
    headptr->flags &= ~(FLAG_INUSE);
  } else {			/* just free it */
    headptr->flags &= ~(FLAG_INUSE);
  }
}