I've read that one of the original Unix shells (Thompson's or Bourne's) used a combination of sbrk()/brk() system calls and SIGSEGV to do dynamic memory allocation for itself. I can't find a reference to this via Google, as any information about old shells and SIGSEGV is swamped by modern people talking about bash and bad programs, or trapping SIGSEGV in scripts or some such. The "heirloom sh" code doesn't have anything like that, but it's clearly been tinkered with, as it uses sigaction(), a BSD innovation.

So, feel free to ignore this vague memory.