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Using malloc() when exploiting the C library
If heap support is required for bare machine C, you must implement _init_alloc() and __rt_heap_extend().
_init_alloc() must
be called first to supply initial heap bounds, and __rt_heap_extend() must be
provided even if it only returns failure. Without __rt_heap_extend(),
certain library functionality is included that causes problems when you
are writing bare machine C.
Prototypes for both _init_alloc() and __rt_heap_extend() are
in rt_heap.h.