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diff --git a/qemu/roms/ipxe/src/arch/i386/interface/pcbios/memtop_umalloc.c b/qemu/roms/ipxe/src/arch/i386/interface/pcbios/memtop_umalloc.c
new file mode 100644
index 000000000..c382e3c36
--- /dev/null
+++ b/qemu/roms/ipxe/src/arch/i386/interface/pcbios/memtop_umalloc.c
@@ -0,0 +1,178 @@
+/*
+ * Copyright (C) 2007 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., 51 Franklin Street, Fifth Floor, Boston, MA
+ * 02110-1301, USA.
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+/**
+ * @file
+ *
+ * External memory allocation
+ *
+ */
+
+#include <limits.h>
+#include <errno.h>
+#include <ipxe/uaccess.h>
+#include <ipxe/hidemem.h>
+#include <ipxe/io.h>
+#include <ipxe/memblock.h>
+#include <ipxe/umalloc.h>
+
+/** Alignment of external allocated memory */
+#define EM_ALIGN ( 4 * 1024 )
+
+/** Equivalent of NOWHERE for user pointers */
+#define UNOWHERE ( ~UNULL )
+
+/** An external memory block */
+struct external_memory {
+	/** Size of this memory block (excluding this header) */
+	size_t size;
+	/** Block is currently in use */
+	int used;
+};
+
+/** Top of heap */
+static userptr_t top = UNULL;
+
+/** Bottom of heap (current lowest allocated block) */
+static userptr_t bottom = UNULL;
+
+/** Remaining space on heap */
+static size_t heap_size;
+
+/**
+ * Initialise external heap
+ *
+ */
+static void init_eheap ( void ) {
+	userptr_t base;
+
+	heap_size = largest_memblock ( &base );
+	bottom = top = userptr_add ( base, heap_size );
+	DBG ( "External heap grows downwards from %lx (size %zx)\n",
+	      user_to_phys ( top, 0 ), heap_size );
+}
+
+/**
+ * Collect free blocks
+ *
+ */
+static void ecollect_free ( void ) {
+	struct external_memory extmem;
+	size_t len;
+
+	/* Walk the free list and collect empty blocks */
+	while ( bottom != top ) {
+		copy_from_user ( &extmem, bottom, -sizeof ( extmem ),
+				 sizeof ( extmem ) );
+		if ( extmem.used )
+			break;
+		DBG ( "EXTMEM freeing [%lx,%lx)\n", user_to_phys ( bottom, 0 ),
+		      user_to_phys ( bottom, extmem.size ) );
+		len = ( extmem.size + sizeof ( extmem ) );
+		bottom = userptr_add ( bottom, len );
+		heap_size += len;
+	}
+}
+
+/**
+ * Reallocate external memory
+ *
+ * @v old_ptr		Memory previously allocated by umalloc(), or UNULL
+ * @v new_size		Requested size
+ * @ret new_ptr		Allocated memory, or UNULL
+ *
+ * Calling realloc() with a new size of zero is a valid way to free a
+ * memory block.
+ */
+static userptr_t memtop_urealloc ( userptr_t ptr, size_t new_size ) {
+	struct external_memory extmem;
+	userptr_t new = ptr;
+	size_t align;
+
+	/* (Re)initialise external memory allocator if necessary */
+	if ( bottom == top )
+		init_eheap();
+
+	/* Get block properties into extmem */
+	if ( ptr && ( ptr != UNOWHERE ) ) {
+		/* Determine old size */
+		copy_from_user ( &extmem, ptr, -sizeof ( extmem ),
+				 sizeof ( extmem ) );
+	} else {
+		/* Create a zero-length block */
+		if ( heap_size < sizeof ( extmem ) ) {
+			DBG ( "EXTMEM out of space\n" );
+			return UNULL;
+		}
+		ptr = bottom = userptr_add ( bottom, -sizeof ( extmem ) );
+		heap_size -= sizeof ( extmem );
+		DBG ( "EXTMEM allocating [%lx,%lx)\n",
+		      user_to_phys ( ptr, 0 ), user_to_phys ( ptr, 0 ) );
+		extmem.size = 0;
+	}
+	extmem.used = ( new_size > 0 );
+
+	/* Expand/shrink block if possible */
+	if ( ptr == bottom ) {
+		/* Update block */
+		if ( new_size > ( heap_size - extmem.size ) ) {
+			DBG ( "EXTMEM out of space\n" );
+			return UNULL;
+		}
+		new = userptr_add ( ptr, - ( new_size - extmem.size ) );
+		align = ( user_to_phys ( new, 0 ) & ( EM_ALIGN - 1 ) );
+		new_size += align;
+		new = userptr_add ( new, -align );
+		DBG ( "EXTMEM expanding [%lx,%lx) to [%lx,%lx)\n",
+		      user_to_phys ( ptr, 0 ),
+		      user_to_phys ( ptr, extmem.size ),
+		      user_to_phys ( new, 0 ),
+		      user_to_phys ( new, new_size ));
+		memmove_user ( new, 0, ptr, 0, ( ( extmem.size < new_size ) ?
+						 extmem.size : new_size ) );
+		bottom = new;
+		heap_size -= ( new_size - extmem.size );
+		extmem.size = new_size;
+	} else {
+		/* Cannot expand; can only pretend to shrink */
+		if ( new_size > extmem.size ) {
+			/* Refuse to expand */
+			DBG ( "EXTMEM cannot expand [%lx,%lx)\n",
+			      user_to_phys ( ptr, 0 ),
+			      user_to_phys ( ptr, extmem.size ) );
+			return UNULL;
+		}
+	}
+
+	/* Write back block properties */
+	copy_to_user ( new, -sizeof ( extmem ), &extmem,
+		       sizeof ( extmem ) );
+
+	/* Collect any free blocks and update hidden memory region */
+	ecollect_free();
+	hide_umalloc ( user_to_phys ( bottom, ( ( bottom == top ) ?
+						0 : -sizeof ( extmem ) ) ),
+		       user_to_phys ( top, 0 ) );
+
+	return ( new_size ? new : UNOWHERE );
+}
+
+PROVIDE_UMALLOC ( memtop, urealloc, memtop_urealloc );