Under Windows systems, it is possible to specify the program heap size from gnatlink using either:
$ gnatlink hello -Xlinker --heap=0x10000,0x1000
This sets the heap reserve size to 0x10000 bytes and the heap commit size to 0x1000 bytes.
$ gnatlink hello -Wl,--heap=0x1000000
This sets the heap reserve size to 0x1000000 bytes. Note that with -Wl option it is not possible to set the heap commit size because the coma is a separator for this option.