Addressing in Object Ada v/s GNAT (2013) showing Vast Differences

[Lucas Redding <lucas.redding@gmail.com>]

Hi

I was wondering how the addressing mechanism works in GNAT Ada? Is it so vastly different to Object Ada? Is there a way I can tailor the GNAT addressing mechanism to follow that of Object Ada?

I have a program that runs perfectly in Object Ada. The program relies heavily on "USE AT" clauses together with 'SIZE on underlying type definition. This is in order to map directly and deterministically to memory with bit precision. The data is independently produced so this is very important.

I have compiled the program is GNAT Ada but I am getting run time errors such as "misaligned address value". More worryingly, any data read from memory that relies on the addressing mechanisms described above is incoherent.

I am interested in moving to GNAT Ada because I believe the accompanying toolset is much richer and therefore more productive but I am beginning to wonder whether this is too onerous task?

Any help is greatly appreciated.

Lucas