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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: GNAT: Why does a large 'new' allocation blow the stack when an
 initialiser is present ?
Date: Fri, 01 Nov 2013 08:45:51 +0000
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Date: 2013-11-01T08:45:51+00:00
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Rod Kay <rodakay@internode.on.net> writes:

> Hi all,
>
>    Is this a bug ?
>
> procedure bug_Test
> is
>    type Integer_array is array (Integer range <>) of Integer;
>    
>    the_Array_1 : access Integer_array 
>       := new Integer_array  (1 .. 10_000_000);         -- Fine.
>
>    the_Array_2 : access Integer_array
>       := new Integer_array' (1 .. 10_000_000 => <>);   -- Stack overflow.
>
> begin 
>    null;
> end;
>
>    It seems that, with the initialiser, GNAT is creating the array on
>    the stack before copying it to the final heap memory ?

Not sure precisely what the bug is, but something odd is going on.

This is on a Mac with GNAT GPL 2013.

The stack overflow occurs with an array length 2**21 but not 2**20.

The traceback shows it happening at the start of the procedure (line
"procedure bug_Test"). I put the declarations into their own declare
blocks with Put_Lines, and the first never got executed.

I'm not sure what "=> <>" is expected to do when there's no default
value; I added "with Default_Component_Value => 42" to Integer_Array,
and The_Array_1 (0) was 42 but The_Array_2 (1) was unchanged at 0!