8.4.3 --defsym=_min_heap_size=size

The default linker script provides a heap size of 0 bytes. Use the --defsym option to define the _min_heap_size symbol to change this default size value. The linker creates a heap with a size defined by this value.

xc32-gcc foo.c -Wl,--defsym=_min_heap_size=2048