How to call a "C" function that is implemented in a ROM (or at an address) from ADA? -

i have question way call "c" function in rom, looking way without involving link-time changes.

for example, know "c" function:

int my_func(int a);  

is located @ address 0xffff_aaaa;

so try:

type rom_my_func access function (a : interfaces.c.int) return interfaces.c.int;  pragma convention (c, rom_my_func);  ada_my_func : rom_my_func := 16#ffff_aaaa#; 

the error can't around assignment of ada_my_func, unsure if there typecast, , attempt @ using system.address_to_access_conversions did not prove successful either.

any pointer(s) examples and/or appreciated.

if you’re using modern gnat , ada2012 can say

function my_func (a : interfaces.c.int) return interfaces.c.int   import,   convention => c,   address => system'to_address (16#ffff_aaaa#); 

note system’to_address gnat-specific; use system.storage_elements.to_address.

i ran program using under gdb , got

(gdb) run starting program: /users/simon/tmp/so/asker   program received signal sigsegv, segmentation fault. 0x00000000ffffaaaa in ?? () 

so it’s done right thing.

without using ada2012 aspects, write

function my_func (a : interfaces.c.int) return interfaces.c.int; pragma import (c, my_func); my_func'address use system'to_address (16#ffff_aaaa#);