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/*
* malloc.c
*
* Very simple linked-list based malloc()/free().
*/
#include <stdlib.h>
#include <string.h>
#include <com32.h>
#include <syslinux/memscan.h>
#include "malloc.h"
struct free_arena_header __malloc_head = {
{
ARENA_TYPE_HEAD,
0,
&__malloc_head,
&__malloc_head,
},
&__malloc_head,
&__malloc_head
};
/* This is extern so it can be overridden by the user application */
extern size_t __stack_size;
extern void *__mem_end; /* Produced after argv parsing */
static inline size_t sp(void)
{
size_t sp;
asm volatile ("movl %%esp,%0":"=rm" (sp));
return sp;
}
#define E820_MEM_MAX 0xfff00000 /* 4 GB - 1 MB */
static int consider_memory_area(void *dummy, addr_t start,
addr_t len, bool valid)
{
struct free_arena_header *fp;
addr_t end;
(void)dummy;
if (valid && start < E820_MEM_MAX) {
if (len > E820_MEM_MAX - start)
len = E820_MEM_MAX - start;
end = start + len;
if (end > __com32.cs_memsize) {
if (start <= __com32.cs_memsize) {
start = __com32.cs_memsize;
len = end - start;
}
if (len >= 2 * sizeof(struct arena_header)) {
fp = (struct free_arena_header *)start;
fp->a.size = len;
__inject_free_block(fp);
}
}
}
return 0;
}
static void __constructor init_memory_arena(void)
{
struct free_arena_header *fp;
size_t start, total_space;
start = (size_t) ARENA_ALIGN_UP(__mem_end);
total_space = sp() - start;
if (__stack_size == 0 || __stack_size > total_space >> 1)
__stack_size = total_space >> 1; /* Half for the stack, half for the heap... */
if (total_space < __stack_size + 4 * sizeof(struct arena_header))
__stack_size = total_space - 4 * sizeof(struct arena_header);
fp = (struct free_arena_header *)start;
fp->a.size = total_space - __stack_size;
__inject_free_block(fp);
/* Scan the memory map to look for other suitable regions */
if (!__com32.cs_memsize)
return; /* Old Syslinux core, can't do this... */
syslinux_scan_memory(consider_memory_area, NULL);
}
static void *__malloc_from_block(struct free_arena_header *fp, size_t size)
{
size_t fsize;
struct free_arena_header *nfp, *na;
fsize = fp->a.size;
/* We need the 2* to account for the larger requirements of a free block */
if (fsize >= size + 2 * sizeof(struct arena_header)) {
/* Bigger block than required -- split block */
nfp = (struct free_arena_header *)((char *)fp + size);
na = fp->a.next;
nfp->a.type = ARENA_TYPE_FREE;
nfp->a.size = fsize - size;
fp->a.type = ARENA_TYPE_USED;
fp->a.size = size;
/* Insert into all-block chain */
nfp->a.prev = fp;
nfp->a.next = na;
na->a.prev = nfp;
fp->a.next = nfp;
/* Replace current block on free chain */
nfp->next_free = fp->next_free;
nfp->prev_free = fp->prev_free;
fp->next_free->prev_free = nfp;
fp->prev_free->next_free = nfp;
} else {
/* Allocate the whole block */
fp->a.type = ARENA_TYPE_USED;
/* Remove from free chain */
fp->next_free->prev_free = fp->prev_free;
fp->prev_free->next_free = fp->next_free;
}
return (void *)(&fp->a + 1);
}
void *malloc(size_t size)
{
struct free_arena_header *fp;
if (size == 0)
return NULL;
/* Add the obligatory arena header, and round up */
size = (size + 2 * sizeof(struct arena_header) - 1) & ARENA_SIZE_MASK;
for (fp = __malloc_head.next_free; fp->a.type != ARENA_TYPE_HEAD;
fp = fp->next_free) {
if (fp->a.size >= size) {
/* Found fit -- allocate out of this block */
return __malloc_from_block(fp, size);
}
}
/* Nothing found... need to request a block from the kernel */
return NULL; /* No kernel to get stuff from */
}
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