basemem.c revision 1b8adde7ba7d5e04395c141c5400dc2cffd7d809
#include "etherboot.h"
#define DEBUG_BASEMEM
/* Routines to allocate base memory in a BIOS-compatible way, by
* updating the Free Base Memory Size counter at 40:13h.
*
* Michael Brown <mbrown@fensystems.co.uk> (mcb30)
* $Id: basemem.c,v 1.5 2004/06/17 12:48:08 fengshuo Exp $
*/
#define fbms ( ( uint16_t * ) phys_to_virt ( 0x413 ) )
#define BASE_MEMORY_MAX ( 640 )
#define FREE_BLOCK_MAGIC ( ('!'<<0) + ('F'<<8) + ('R'<<16) + ('E'<<24) )
typedef struct free_base_memory_block {
uint32_t magic;
uint16_t size_kb;
} free_base_memory_block_t;
/* Return amount of free base memory in bytes
*/
uint32_t get_free_base_memory ( void ) {
return *fbms << 10;
}
/* Adjust the real mode stack pointer. We keep the real mode stack at
* the top of free base memory, rather than allocating space for it.
*/
static inline void adjust_real_mode_stack ( void ) {
/* real_mode_stack = ( *fbms << 10 ); */
}
/* Allocate N bytes of base memory. Amount allocated will be rounded
* up to the nearest kB, since that's the granularity of the BIOS FBMS
* counter. Returns NULL if memory cannot be allocated.
*/
void * allot_base_memory ( size_t size ) {
uint16_t size_kb = ( size + 1023 ) >> 10;
void *ptr = NULL;
#ifdef DEBUG_BASEMEM
printf ( "Trying to allocate %d kB of base memory, %d kB free\n",
size_kb, *fbms );
#endif
/* Free up any unused memory before we start */
free_unused_base_memory();
/* Check available base memory */
if ( size_kb > *fbms ) { return NULL; }
/* Reduce available base memory */
*fbms -= size_kb;
/* Calculate address of memory allocated */
ptr = phys_to_virt ( *fbms << 10 );
#ifdef DEBUG_BASEMEM
/* Zero out memory. We do this so that allocation of
* already-used space will show up in the form of a crash as
* soon as possible.
*/
memset ( ptr, 0, size_kb << 10 );
#endif
/* Adjust real mode stack pointer */
adjust_real_mode_stack ();
return ptr;
}
/* Free base memory allocated by allot_base_memory. The BIOS provides
* nothing better than a LIFO mechanism for freeing memory (i.e. it
* just has the single "total free memory" counter), but we improve
* upon this slightly; as long as you free all the allotted blocks, it
* doesn't matter what order you free them in. (This will only work
* for blocks that are freed via forget_base_memory()).
*
* Yes, it's annoying that you have to remember the size of the blocks
* you've allotted. However, since our granularity of allocation is
* 1K, the alternative is to risk wasting the occasional kB of base
* memory, which is a Bad Thing. Really, you should be using as
* little base memory as possible, so consider the awkwardness of the
* API to be a feature! :-)
*/
void forget_base_memory ( void *ptr, size_t size ) {
uint16_t remainder = virt_to_phys(ptr) & 1023;
uint16_t size_kb = ( size + remainder + 1023 ) >> 10;
free_base_memory_block_t *free_block =
( free_base_memory_block_t * ) ( ptr - remainder );
if ( ( ptr == NULL ) || ( size == 0 ) ) { return; }
#ifdef DEBUG_BASEMEM
printf ( "Trying to free %d bytes base memory at 0x%x\n",
size, virt_to_phys ( ptr ) );
if ( remainder > 0 ) {
printf ( "WARNING: destructively expanding free block "
"downwards to 0x%x\n",
virt_to_phys ( ptr - remainder ) );
}
#endif
/* Mark every kilobyte within this block as free. This is
* overkill for normal purposes, but helps when something has
* allocated base memory with a granularity finer than the
* BIOS granularity of 1kB. PXE ROMs tend to do this when
* they allocate their own memory. This method allows us to
* free their blocks (admittedly in a rather dangerous,
* tread-on-anything-either-side sort of way, but there's no
* other way to do it).
*
* Since we're marking every kB as free, there's actually no
* need for recording the size of the blocks. However, we
* keep this in so that debug messages are friendlier. It
* probably adds around 8 bytes to the overall code size.
*/
while ( size_kb > 0 ) {
/* Mark this block as unused */
free_block->magic = FREE_BLOCK_MAGIC;
free_block->size_kb = size_kb;
/* Move up by 1 kB */
free_block = (void *)free_block + ( 1 << 10 );
size_kb--;
}
/* Free up unused base memory */
free_unused_base_memory();
}
/* Do the actual freeing of memory. This is split out from
* forget_base_memory() so that it may be called separately. It
* should be called whenever base memory is deallocated by an external
* entity (if we can detect that it has done so) so that we get the
* chance to free up our own blocks.
*/
void free_unused_base_memory ( void ) {
free_base_memory_block_t *free_block = NULL;
/* Try to release memory back to the BIOS. Free all
* consecutive blocks marked as free.
*/
while ( 1 ) {
/* Calculate address of next potential free block */
free_block = ( free_base_memory_block_t * )
phys_to_virt ( *fbms << 10 );
/* Stop processing if we're all the way up to 640K or
* if this is not a free block
*/
if ( ( *fbms == BASE_MEMORY_MAX ) ||
( free_block->magic != FREE_BLOCK_MAGIC ) ) {
break;
}
/* Return memory to BIOS */
*fbms += free_block->size_kb;
#ifdef DEBUG_BASEMEM
printf ( "Freed %d kB base memory, %d kB now free\n",
free_block->size_kb, *fbms );
/* Zero out freed block. We do this in case
* the block contained any structures that
* might be located by scanning through
* memory.
*/
memset ( free_block, 0, free_block->size_kb << 10 );
#endif
}
/* Adjust real mode stack pointer */
adjust_real_mode_stack ();
}