program error (exception access violation) in windows

["ldb" <ldb_nospam@hotmail.com>]

> raised PROGRAM_ERROR : EXCEPTION_ACCESS_VIOLATION

We have tried, in numerous ways, to come up with an ada library that
can be used by c programs. The ada program needs to return a pretty
large and ugly dynamic structure. For the sake of discussion, think of
it as an array of structs (with pointers to dynamic sub-arrays).

I've gotten it to work flawlessly under linux using shared libraries. I
use a combination of importing malloc() and the
Ada.Address_To_Access_Conversions package. In this way, I can malloc
the correctly sized eventual c data-structure, and use the created
access from that package to populate the data structure. When I return
the address of that to C, everything appears to work fine. I can free
it like any other C data structure.

It seems to fail (sometimes) when I move it to windows (using a c
program and my ada-based dll), resulting in the above exception. When I
remove the free calls, in c, everything works fine (and memory leaks).
I have a 'minimal' program that uses a simple array of integers, and it
seems to work fine, but for our main program, it still crashes.
Tommorow, I'm going to rip apart our program to see if I can find a
minimal example of the crashing behavior.

We've tried numerous different ways of allocating the memory in ada,
and free'ing it in C. We even got a smiliar error when we tried
allocating it in Ada, and free'ing it in Ada through another C call to
the ada library. We are about to change our interface from Ada to
single elements, only, and have C wrapper functions that do all the
allocating and query for each single value to populate the data
structure.

Has anyone heard of issues like this? Or have a possible guess as to
what is going on?