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- #include "stdint.h"
- #include "stddef.h"
- #include "memsizes.h"
- #include "etherboot.h"
- #include "basemem.h"
-
- /* 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)
- *
- * We no longer have anything to do with the real-mode stack. The
- * only code that can end up creating a huge bubble of wasted base
- * memory is the UNDI driver, so we make it the responsibility of the
- * UNDI driver to reallocate the real-mode stack if required.
- */
-
- /* "fbms" is an alias to the BIOS FBMS counter at 40:13, and acts just
- * like any other uint16_t. We can't be used under -DKEEP_IT_REAL
- * anyway, so we may as well be efficient.
- */
- #define fbms ( * ( ( uint16_t * ) phys_to_virt ( 0x413 ) ) )
- #define FBMS_MAX ( 640 )
-
- /* Structure that we use to represent a free block of base memory
- */
- #define FREE_BLOCK_MAGIC ( ('!'<<0) + ('F'<<8) + ('R'<<16) + ('E'<<24) )
- union free_base_memory_block {
- struct {
- uint32_t magic;
- uint16_t size_kb;
- };
- char bytes[1024];
- };
-
- /* Local prototypes */
- static void free_unused_base_memory ( void );
-
- #undef DBG
- #ifdef DEBUG_BASEMEM
- #define DBG(...) printf ( __VA_ARGS__ )
- #else
- #define DBG(...)
- #endif
-
- /*
- * Return amount of free base memory in bytes
- *
- */
- uint32_t get_free_base_memory ( void ) {
- return 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 * alloc_base_memory ( size_t size ) {
- uint16_t size_kb = ( size + 1023 ) >> 10;
- void *ptr;
-
- DBG ( "Trying to allocate %d bytes of base memory from %d kB free\n",
- size, fbms );
-
- /* Free up any unused memory before we start */
- free_unused_base_memory();
-
- /* Check available base memory */
- if ( size_kb > fbms ) {
- DBG ( "Could not allocate %d kB of base memory: "
- "only %d kB free\n", size_kb, fbms );
- return NULL;
- }
-
- /* Reduce available base memory */
- fbms -= size_kb;
-
- /* Calculate address of memory allocated */
- ptr = phys_to_virt ( fbms << 10 );
-
- /* 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.
- *
- * Update: there's another reason for doing this. If we don't
- * zero the contents, then they could still retain our "free
- * block" markers and be liable to being freed whenever a
- * base-memory allocation routine is next called.
- */
- memset ( ptr, 0, size_kb << 10 );
-
- DBG ( "Allocated %d kB of base memory at [%hx:0000,%hx:0000)\n",
- size_kb, ( fbms << 6 ), ( ( fbms + size_kb ) << 6 ) );
-
- /* Update our memory map */
- get_memsizes();
-
- return ptr;
- }
-
- /* Free base memory allocated by alloc_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 allocated blocks, it
- * doesn't matter what order you free them in. (This will only work
- * for blocks that are freed via free_base_memory()).
- *
- * Yes, it's annoying that you have to remember the size of the blocks
- * you've allocated. 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 free_base_memory ( void *ptr, size_t size ) {
- uint16_t remainder = virt_to_phys ( ptr ) & 1023;
- uint16_t size_kb = ( size + remainder + 1023 ) >> 10;
- union free_base_memory_block *free_block =
- ( ( void * ) ( ptr - remainder ) );
-
- if ( ( ptr == NULL ) || ( size == 0 ) ) {
- return;
- }
-
- DBG ( "Trying to free %d bytes base memory at %hx:%hx\n", size,
- ( virt_to_phys ( ptr - remainder ) >> 4 ),
- ( virt_to_phys ( ptr - remainder ) & 0xf ) + remainder );
-
- /* 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.
- */
- for ( ; size_kb > 0 ; free_block++, size_kb-- ) {
- /* Mark this block as unused */
- free_block->magic = FREE_BLOCK_MAGIC;
- free_block->size_kb = size_kb;
- }
-
- /* Free up unused base memory */
- free_unused_base_memory();
-
- /* Update our memory map */
- get_memsizes();
-
- DBG ( "%d kB of base memory now free\n", fbms );
- }
-
- /* Do the actual freeing of memory. This is split out from
- * free_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.
- */
- static void free_unused_base_memory ( void ) {
- union free_base_memory_block *free_block;
-
- /* 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 = 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 == FBMS_MAX ) ||
- ( free_block->magic != FREE_BLOCK_MAGIC ) ) {
- break;
- }
-
- /* Return memory to BIOS */
- fbms += free_block->size_kb;
-
- DBG ( "Freed %d kB of base memory at [%hx:0000,%hx:0000)\n",
- free_block->size_kb, ( fbms << 6 ),
- ( fbms + free_block->size_kb ) << 6 );
-
- /* 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 );
-
- }
- }
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