Create an object at a given address
You are encouraged to solve this task according to the task description, using any language you may know.
In systems programing it is sometimes required to place language objects at specific memory locations, like I/O registers, hardware interrupt vectors etc.
Task
Show how language objects can be allocated at a specific machine addresses.
Since most OSes prohibit access to the physical memory if it is not mapped by the application, as an example, rather than a physical address, take the address of some existing object. E.g. create an integer object. Print the machine address of the object. Take the address of the object and create another integer object at this address. Print the value of this object to verify that it is same as one of the origin. Change the value of the origin and verify it again.
Ada
In Ada object address can be specified using the address representation clause RM 13.3: <lang ada> type IO_Port is mod 2**8; -- One byte Device_Port : type IO_Port; for Device_Port'Address use 16#FFFF_F000#; </lang> In the example above the address is specified constant. It is also possible to specify address dynamically as the following solution of the task does: <lang ada> with Ada.Text_IO; use Ada.Text_IO; with System.Storage_Elements; use System.Storage_Elements;
procedure Test_Address is
X : Integer := 123; Y : Integer; for Y'Address use X'Address;
begin
Put_Line ("At address:" & Integer_Address'Image (To_Integer (Y'Address)));
Put_Line (Integer'Image (Y));
X := 456;
Put_Line (Integer'Image (Y));
end Test_Address; </lang> Sample output:
At address: 38207236 123 456