Question

I’m experiencing what appears to be a stack/heap collision in an embedded environment (see this question for some background).

I’d like to try rewriting the code so that it doesn’t allocate memory on the heap.

Can I write an application without using the heap in C? For example, how would I use the stack only if I have a need for dynamic memory allocation?

Answer 1

I did it once in an embedded environment where we were writing “super safe” code for biomedical machines.
Malloc()s were explicitly forbidden, partly for the resources limits and for the unexpected behavior you can get from dynamic memory (look for malloc(), VxWorks/Tornado and fragmentation and you’ll have a good example).

Anyway, the solution was to plan in advance the needed resources and statically allocate the “dynamic” ones in a vector contained in a separate module, having some kind of special purpose allocator give and take back pointers. This approach avoided fragmentation issues altogether and helped getting finer grained error info, if a resource was exhausted.

This may sound silly on big iron, but on embedded systems, and particularly on safety critical ones, it’s better to have a very good understanding of which -time and space- resources are needed beforehand, if only for the purpose of sizing the hardware.