While working with glibc I tried to reduce the data segment using sbrk using a negative parameter, and found a most strange behaviour. I first malloc, then free it, then reduce data segment with sbrk,...

For learning purposes, I'm trying to implement a stack in the heap memory. When I push something I just need to do the systemcall sbrk, and that's fine. When I proceed with a pop I can retrive my valu...