malloc.c

/*
 * Copyright (C) 2006 Michael Brown <mbrown@fensystems.co.uk>.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License as
 * published by the Free Software Foundation; either version 2 of the
 * License, or any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

FILE_LICENCE ( GPL2_OR_LATER );

#include <stddef.h>
#include <stdint.h>
#include <string.h>
#include <strings.h>
#include <ipxe/io.h>
#include <ipxe/list.h>
#include <ipxe/init.h>
#include <ipxe/malloc.h>

/** @file
 *
 * Dynamic memory allocation
 *
 */

/** A free block of memory */
struct memory_block {
	/** List of free blocks */
	struct list_head list;
	/** Size of this block */
	size_t size;
};

#define MIN_MEMBLOCK_SIZE \
	( ( size_t ) ( 1 << ( fls ( sizeof ( struct memory_block ) - 1 ) ) ) )

/** A block of allocated memory complete with size information */
struct autosized_block {
	/** Size of this block */
	size_t size;
	/** Remaining data */
	char data[0];
};

/**
 * Address for zero-length memory blocks
 *
 * @c malloc(0) or @c realloc(ptr,0) will return the special value @c
 * NOWHERE.  Calling @c free(NOWHERE) will have no effect.
 *
 * This is consistent with the ANSI C standards, which state that
 * "either NULL or a pointer suitable to be passed to free()" must be
 * returned in these cases.  Using a special non-NULL value means that
 * the caller can take a NULL return value to indicate failure,
 * without first having to check for a requested size of zero.
 *
 * Code outside of malloc.c do not ever need to refer to the actual
 * value of @c NOWHERE; this is an internal definition.
 */
#define NOWHERE ( ( void * ) ~( ( intptr_t ) 0 ) )

/** List of free memory blocks */
static LIST_HEAD ( free_blocks );

/** Total amount of free memory */
size_t freemem;

/**
 * Heap size
 *
 * Currently fixed at 128kB.
 */
#define HEAP_SIZE ( 128 * 1024 )

/** The heap itself */
static char heap[HEAP_SIZE] __attribute__ (( aligned ( __alignof__(void *) )));

/**
 * Allocate a memory block
 *
 * @v size		Requested size
 * @v align		Physical alignment
 * @ret ptr		Memory block, or NULL
 *
 * Allocates a memory block @b physically aligned as requested.  No
 * guarantees are provided for the alignment of the virtual address.
 *
 * @c align must be a power of two.  @c size may not be zero.
 */
void * alloc_memblock ( size_t size, size_t align ) {
	struct memory_block *block;
	size_t align_mask;
	size_t pre_size;
	ssize_t post_size;
	struct memory_block *pre;
	struct memory_block *post;

	/* Round up size to multiple of MIN_MEMBLOCK_SIZE and
	 * calculate alignment mask.
	 */
	size = ( size + MIN_MEMBLOCK_SIZE - 1 ) & ~( MIN_MEMBLOCK_SIZE - 1 );
	align_mask = ( align - 1 ) | ( MIN_MEMBLOCK_SIZE - 1 );

	DBG ( "Allocating %#zx (aligned %#zx)\n", size, align );

	/* Search through blocks for the first one with enough space */
	list_for_each_entry ( block, &free_blocks, list ) {
		pre_size = ( - virt_to_phys ( block ) ) & align_mask;
		post_size = block->size - pre_size - size;
		if ( post_size >= 0 ) {
			/* Split block into pre-block, block, and
			 * post-block.  After this split, the "pre"
			 * block is the one currently linked into the
			 * free list.
			 */
			pre   = block;
			block = ( ( ( void * ) pre   ) + pre_size );
			post  = ( ( ( void * ) block ) + size     );
			DBG ( "[%p,%p) -> [%p,%p) + [%p,%p)\n", pre,
			      ( ( ( void * ) pre ) + pre->size ), pre, block,
			      post, ( ( ( void * ) pre ) + pre->size ) );
			/* If there is a "post" block, add it in to
			 * the free list.  Leak it if it is too small
			 * (which can happen only at the very end of
			 * the heap).
			 */
			if ( ( size_t ) post_size >= MIN_MEMBLOCK_SIZE ) {
				post->size = post_size;
				list_add ( &post->list, &pre->list );
			}
			/* Shrink "pre" block, leaving the main block
			 * isolated and no longer part of the free
			 * list.
			 */
			pre->size = pre_size;
			/* If there is no "pre" block, remove it from
			 * the list.  Also remove it (i.e. leak it) if
			 * it is too small, which can happen only at
			 * the very start of the heap.
			 */
			if ( pre_size < MIN_MEMBLOCK_SIZE )
				list_del ( &pre->list );
			/* Update total free memory */
			freemem -= size;
			/* Return allocated block */
			DBG ( "Allocated [%p,%p)\n", block,
			      ( ( ( void * ) block ) + size ) );
			return block;
		}
	}

	DBG ( "Failed to allocate %#zx (aligned %#zx)\n", size, align );
	return NULL;
}

/**
 * Free a memory block
 *
 * @v ptr		Memory allocated by alloc_memblock(), or NULL
 * @v size		Size of the memory
 *
 * If @c ptr is NULL, no action is taken.
 */
void free_memblock ( void *ptr, size_t size ) {
	struct memory_block *freeing;
	struct memory_block *block;
	ssize_t gap_before;
	ssize_t gap_after = -1;

	/* Allow for ptr==NULL */
	if ( ! ptr )
		return;

	/* Round up size to match actual size that alloc_memblock()
	 * would have used.
	 */
	size = ( size + MIN_MEMBLOCK_SIZE - 1 ) & ~( MIN_MEMBLOCK_SIZE - 1 );
	freeing = ptr;
	freeing->size = size;
	DBG ( "Freeing [%p,%p)\n", freeing, ( ( ( void * ) freeing ) + size ));

	/* Insert/merge into free list */
	list_for_each_entry ( block, &free_blocks, list ) {
		/* Calculate gaps before and after the "freeing" block */
		gap_before = ( ( ( void * ) freeing ) - 
			       ( ( ( void * ) block ) + block->size ) );
		gap_after = ( ( ( void * ) block ) - 
			      ( ( ( void * ) freeing ) + freeing->size ) );
		/* Merge with immediately preceding block, if possible */
		if ( gap_before == 0 ) {
			DBG ( "[%p,%p) + [%p,%p) -> [%p,%p)\n", block,
			      ( ( ( void * ) block ) + block->size ), freeing,
			      ( ( ( void * ) freeing ) + freeing->size ),block,
			      ( ( ( void * ) freeing ) + freeing->size ) );
			block->size += size;
			list_del ( &block->list );
			freeing = block;
		}
		/* Stop processing as soon as we reach a following block */
		if ( gap_after >= 0 )
			break;
	}

	/* Insert before the immediately following block.  If
	 * possible, merge the following block into the "freeing"
	 * block.
	 */
	DBG ( "[%p,%p)\n", freeing, ( ( ( void * ) freeing ) + freeing->size));
	list_add_tail ( &freeing->list, &block->list );
	if ( gap_after == 0 ) {
		DBG ( "[%p,%p) + [%p,%p) -> [%p,%p)\n", freeing,
		      ( ( ( void * ) freeing ) + freeing->size ), block,
		      ( ( ( void * ) block ) + block->size ), freeing,
		      ( ( ( void * ) block ) + block->size ) );
		freeing->size += block->size;
		list_del ( &block->list );
	}

	/* Update free memory counter */
	freemem += size;
}

/**
 * Reallocate memory
 *
 * @v old_ptr		Memory previously allocated by malloc(), or NULL
 * @v new_size		Requested size
 * @ret new_ptr		Allocated memory, or NULL
 *
 * Allocates memory with no particular alignment requirement.  @c
 * new_ptr will be aligned to at least a multiple of sizeof(void*).
 * If @c old_ptr is non-NULL, then the contents of the newly allocated
 * memory will be the same as the contents of the previously allocated
 * memory, up to the minimum of the old and new sizes.  The old memory
 * will be freed.
 *
 * If allocation fails the previously allocated block is left
 * untouched and NULL is returned.
 *
 * Calling realloc() with a new size of zero is a valid way to free a
 * memory block.
 */
void * realloc ( void *old_ptr, size_t new_size ) {
	struct autosized_block *old_block;
	struct autosized_block *new_block;
	size_t old_total_size;
	size_t new_total_size;
	size_t old_size;
	void *new_ptr = NOWHERE;

	/* Allocate new memory if necessary.  If allocation fails,
	 * return without touching the old block.
	 */
	if ( new_size ) {
		new_total_size = ( new_size +
				   offsetof ( struct autosized_block, data ) );
		new_block = alloc_memblock ( new_total_size, 1 );
		if ( ! new_block )
			return NULL;
		new_block->size = new_total_size;
		new_ptr = &new_block->data;
	}
	
	/* Copy across relevant part of the old data region (if any),
	 * then free it.  Note that at this point either (a) new_ptr
	 * is valid, or (b) new_size is 0; either way, the memcpy() is
	 * valid.
	 */
	if ( old_ptr && ( old_ptr != NOWHERE ) ) {
		old_block = container_of ( old_ptr, struct autosized_block,
					   data );
		old_total_size = old_block->size;
		old_size = ( old_total_size -
			     offsetof ( struct autosized_block, data ) );
		memcpy ( new_ptr, old_ptr,
			 ( ( old_size < new_size ) ? old_size : new_size ) );
		free_memblock ( old_block, old_total_size );
	}

	return new_ptr;
}

/**
 * Allocate memory
 *
 * @v size		Requested size
 * @ret ptr		Memory, or NULL
 *
 * Allocates memory with no particular alignment requirement.  @c ptr
 * will be aligned to at least a multiple of sizeof(void*).
 */
void * malloc ( size_t size ) {
	return realloc ( NULL, size );
}

/**
 * Free memory
 *
 * @v ptr		Memory allocated by malloc(), or NULL
 *
 * Memory allocated with malloc_dma() cannot be freed with free(); it
 * must be freed with free_dma() instead.
 *
 * If @c ptr is NULL, no action is taken.
 */
void free ( void *ptr ) {
	realloc ( ptr, 0 );
}

/**
 * Allocate cleared memory
 *
 * @v size		Requested size
 * @ret ptr		Allocated memory
 *
 * Allocate memory as per malloc(), and zero it.
 *
 * This function name is non-standard, but pretty intuitive.
 * zalloc(size) is always equivalent to calloc(1,size)
 */
void * zalloc ( size_t size ) {
	void *data;

	data = malloc ( size );
	if ( data )
		memset ( data, 0, size );
	return data;
}

/**
 * Add memory to allocation pool
 *
 * @v start		Start address
 * @v end		End address
 *
 * Adds a block of memory [start,end) to the allocation pool.  This is
 * a one-way operation; there is no way to reclaim this memory.
 *
 * @c start must be aligned to at least a multiple of sizeof(void*).
 */
void mpopulate ( void *start, size_t len ) {
	/* Prevent free_memblock() from rounding up len beyond the end
	 * of what we were actually given...
	 */
	free_memblock ( start, ( len & ~( MIN_MEMBLOCK_SIZE - 1 ) ) );
}

/**
 * Initialise the heap
 *
 */
static void init_heap ( void ) {
	mpopulate ( heap, sizeof ( heap ) );
}

/** Memory allocator initialisation function */
struct init_fn heap_init_fn __init_fn ( INIT_EARLY ) = {
	.initialise = init_heap,
};

#if 0
#include <stdio.h>
/**
 * Dump free block list
 *
 */
void mdumpfree ( void ) {
	struct memory_block *block;

	printf ( "Free block list:\n" );
	list_for_each_entry ( block, &free_blocks, list ) {
		printf ( "[%p,%p] (size %#zx)\n", block,
			 ( ( ( void * ) block ) + block->size ), block->size );
	}
}
#endif