[malloc] Allow allocation of memory with a specified alignment offset

Allow for allocation of memory blocks having a specified offset from a
specified physical alignment, such as being 12 bytes before a 2kB
boundary.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/core/malloc.c

@@ -220,6 +220,7 @@ static void discard_all_cache ( void ) {
  *
  * @v size		Requested size
  * @v align		Physical alignment
+ * @v offset		Offset from physical alignment
  * @ret ptr		Memory block, or NULL
  *
  * Allocates a memory block @b physically aligned as requested.  No
@@ -227,7 +228,7 @@ static void discard_all_cache ( void ) {
  *
  * @c align must be a power of two.  @c size may not be zero.
  */
-void * alloc_memblock ( size_t size, size_t align ) {
+void * alloc_memblock ( size_t size, size_t align, size_t offset ) {
 	struct memory_block *block;
 	size_t align_mask;
 	size_t pre_size;
@@ -244,12 +245,13 @@ void * alloc_memblock ( size_t size, size_t align ) {
 	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 );
+	DBG ( "Allocating %#zx (aligned %#zx+%zx)\n", size, align, offset );
 	while ( 1 ) {
 		/* 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;
+			pre_size = ( ( offset - virt_to_phys ( block ) )
-			post_size = block->size - pre_size - size;
+				     & 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"
@@ -418,7 +420,7 @@ void * realloc ( void *old_ptr, size_t new_size ) {
 	if ( new_size ) {
 		new_total_size = ( new_size +
 				   offsetof ( struct autosized_block, data ) );
-		new_block = alloc_memblock ( new_total_size, 1 );
+		new_block = alloc_memblock ( new_total_size, 1, 0 );
 		if ( ! new_block )
 			return NULL;
 		VALGRIND_MAKE_MEM_UNDEFINED ( new_block, offsetof ( struct autosized_block, data ) );

src/include/ipxe/malloc.h

@@ -23,11 +23,33 @@ FILE_LICENCE ( GPL2_OR_LATER );
 
 extern size_t freemem;
 
-extern void * __malloc alloc_memblock ( size_t size, size_t align );
+extern void * __malloc alloc_memblock ( size_t size, size_t align,
+					size_t offset );
 extern void free_memblock ( void *ptr, size_t size );
 extern void mpopulate ( void *start, size_t len );
 extern void mdumpfree ( void );
 
+/**
+ * Allocate memory for DMA
+ *
+ * @v size		Requested size
+ * @v align		Physical alignment
+ * @v offset		Offset from physical alignment
+ * @ret ptr		Memory, or NULL
+ *
+ * Allocates physically-aligned memory for DMA.
+ *
+ * @c align must be a power of two.  @c size may not be zero.
+ */
+static inline void * __malloc malloc_dma_offset ( size_t size,
+						  size_t phys_align,
+						  size_t offset ) {
+	void * ptr = alloc_memblock ( size, phys_align, offset );
+	if ( ptr && size )
+		VALGRIND_MALLOCLIKE_BLOCK ( ptr, size, 0, 0 );
+	return ptr;
+}
+
 /**
  * Allocate memory for DMA
  *
@@ -40,10 +62,7 @@ extern void mdumpfree ( void );
  * @c align must be a power of two.  @c size may not be zero.
  */
 static inline void * __malloc malloc_dma ( size_t size, size_t phys_align ) {
-	void * ptr = alloc_memblock ( size, phys_align );
+	return malloc_dma_offset ( size, phys_align, 0 );
-	if ( ptr && size )
-		VALGRIND_MALLOCLIKE_BLOCK ( ptr, size, 0, 0 );
-	return ptr;
 }
 
 /**