[U-Boot] Memset 0 in heap initialization?

In common/dlmalloc.c in the heap initialization mem_malloc_init() [1] it looks like the whole heap is initialized with zero:

memset((void *)mem_malloc_start, 0, size);

What's the reason for doing this? I know that the .bss segment has to be zeroed at system start up, but why doing this for the heap, too? It was my understanding that one could make no assumption about the initial content of memory returned by malloc() (?).

Sorry if I miss the obvious ;)

Thanks

Dirk

[1] http://git.denx.de/?p=u-boot.git;a=blob;f=common/dlmalloc.c;h=e9bab09b8eac7c...