Memory initialization (not)

[Jim Dougherty]

Mihai Donțu wrote:
>     On Tuesday 30 September 2008, Jim Dougherty wrote:
>>  I have a section of memory that I do not want to be initialized with
>>  zeros when my program starts.
>>  Is there a way to achieve this?
> 
> I think that zero initialization is a consequence of how the process 
> images is
> created. For example:
> 
> static char a[65536];
> 
> will make the .bss section of size ~65536 bytes which is allocated by the
> dynamic linker by means of mmap() which always provides zeroed-out pages.
> 
> So to answer your question: global variables are likely to be always
> initialized with zero (it's out of gcc-s hands). Stack variables, on the
> other hand, are "initialized" with whatever is on the stack, which yeah, if
> you don't explicitly initialize them, could be called uninitialized. :)
> 
> -- 
> Mihai Donu (unices@bitdefender.com <mailto:unices@bitdefender.com>)

I think that you are wrong although I do not know what the answer is.

I am writing firmware for an embedded system that contains conventional 
general purpose RAM but it also contains a small amount of battery 
backed up RAM.  We store data in the battery backed up RAM that is 
basically permanent, the data is not lost when power is turned off and 
on.  In the case of this battery backed up RAM, we do not want the 
compiler writing over our good data at powerup.

I have to believe that there is a way to do this but I do not know what 
it is?