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