Re: Memory limits in Ada where Fortran has none

["Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk>]

On Wed, 16 Mar 2005 14:51:26 -0500, Robert A Duff wrote:

> "Dr. Adrian Wrigley" <amtw@linuxchip.demon.co.uk.uk.uk> writes:
> 
>> I am very wary of a test like this because GNAT sometimes
>> silently accesses the wrong element of very large data, if I
>> remember correctly.
...
>>... A correctly written program can (and did!)
>> thus fail catastrophically.  Large records in particular are
>> suspect (on GNAT 3.15p, x86). (I have no test case to hand
>> at the moment).  I don't know if it is affected by -gnato
>> and default absence of overflow checking.
> 
> I guess you should send them a bug report.

it wasn't convenient at the time (I had to find a fix!)
maybe I will if I have time to make a test case
on a current compiler.

>> A more comforting test would place a *different* value at
>> each location, and check they are all correct!
> 
> OK, the above example does that (but it's an array,
> not a record).

Sorry I raised this without giving a tangible example.
It was to do with locations of elements, and 'Address,
once the 256MB limit is breached.  I wanted to mmap a
large data set, but various things kept breaking.
The solution I found keeps the record under 256M, and avoids
using 'Address on giant arrays.  Works well now...
except I've hit the 2GB limit on the machine's mmap :(

I don't think hardware or OS issues had anything to do with
the issue, since I fixed it with the help of some C code.
The machine also has ECC, and the fault was repeatable.
-- 
Adrian