Re: Y21C Bug

[kilgallen@eisner.decus.org (Larry Kilgallen)]

Reply-To: Kilgallen@eisner.decus.org.nospam
Organization: LJK Software
Lines: 23

In article <387DFB1E.CBBF14C7@mail.com>, Mats Weber <matsw@mail.com> writes:
> Thierry Lelegard wrote:
> 
>> Yes it does. If you had left the variable uninitialized (on an Ada
>> perspective), then the variable would have been allocated in
>> a "demand zero" section (no allocation in executable). Since
>> you provided an explicit initial value, the compiler/linker placed
>> it into a "copy on reference" section which contains the initial
>> values. Of course, the compiler could make a special optimization
>> which consists in inspecting every single byte of this initial
>> value and if they are all zeroes then place the variable into
>> a "demand zero" section. But, it appears that this optimization
>> is not made.
> 
> You generally cannot guarantee that the variable is allocated in a
> demand-zero region. For instance, when allocated on the stack, the stack
> may have previously grown higher than where you allocate and you get the
> content left there from a previous call (unless the stack is zeroed or
> unmapped from the address space when it shrinks, but I doubt any system
> is doing that).

You cannot guarantee a _stack_ variable is in a demand-zero region,
but you can guarantee it for static variables or by calling $EXPREG.