Alejandro Martinez Alejandro Martinez - 1 year ago 68
Linux Question

Ada program works in Linux but not in GPS Windows 10

Thanks in advance for any help. I am currently doing some beginner work on ada programming and I have installed GNAT Programming Studio (GPS) from
I have Windows 10 64-bits. I was given the following code at school:

pragma Task_Dispatching_Policy(FIFO_Within_Priorities);

with Ada.Text_IO; use Ada.Text_IO;
with Ada.Real_Time; use Ada.Real_Time;

procedure PeriodicTasks is

Start : Time;

package Duration_IO is new Ada.Text_IO.Fixed_IO(Duration);
package Int_IO is new Ada.Text_IO.Integer_IO(Integer);

task type T(Id: Integer; Period : Integer) is
pragma Priority(Id);

task body T is
Next : Time;
X : Integer;
Next := Start;
Next := Next + Milliseconds(Period);
-- Some dummy function
X := 0;
for Index in 1..5000000 loop
X := X + Index;
end loop;
Duration_IO.Put(To_Duration(Clock - Start), 3, 3);
Put(" : ");
Int_IO.Put(Id, 2);
delay until Next;
end loop;
end T;

-- Example Task
Task_P10 : T(10, 250);
Task_P12 : T(12, 500);
Task_P14 : T(14, 500);
Task_P16 : T(16, 250);
Task_P18 : T(18, 500);
Task_P20 : T(20, 250);
Start := Clock;
end PeriodicTasks;

I opened the file in GPS, built it (no errors) and ran it but it doesn't show any printed output. I have heard that sometimes you get issues with multicore CPUs, so everytime the gps.exe is opened, the CPU affinity is set to only one CPU and it is always "Run as Administrator". However, this did not work either, I get no output.
I decided to use Oracle Virtual Box and set up an Ubuntu OS (32 bits) with only one processor. Installed the GNAT tools, compiled with gnatmake, ran with ./periodictasks, and guess what, the program did what it is supposed to do and printed out the info.

After all this long story, does anybody know why this is happening? Could it be a 64 bit vs 32 bit situation?

Thank you very much!

Answer Source

Until recently, GNAT didn't check for integer overflow by default. It did check for constraint errors, e.g. assigning 0 to a Positive.

Many of us thought this was a strange choice by the compiler developers, because it led to many questions whose root cause was failure to handle integer overflow. The recent change leads us to suppose that the developers now agree!

Your problem arises because of the statement

for Index in 1..5000000 loop
   X := X + Index;
end loop;

which would end up with X ~ 10^13, which doesn’t fit in a 32-bit integer (it would fit in a 64-bit integer, but that would be a Long_Long_Integer on most if not all GNAT platforms).

It’s likely that your Windows compiler is GNAT GPL 2016, which shows the new behaviour, while the Ubuntu compiler is an older FSF GCC.

You can tell your Windows compiler to use the old behaviour using the compiler switch -gnato0.

You can tell your Ubuntu compiler to use the new behaviour using the compiler switch -gnato.