This should tell one whether the pointer returned by alloca(3C) is safe to use: #include <sys/time.h> #include <sys/resource.h> #include <stdio.h> int

This should tell one whether the pointer returned by alloca(3C) is safe to use: #include <sys/time.h> #include <sys/resource.h> #include <stdio.h> int main(int argc, char *argv[]) { struct rlimit limit; getrlimit(RLIMIT_STACK, &limit); printf("Stack start at %p, end at %p.\n", &argc, &argc - limit.rlim_cur); return(0); } % cc limit.c -o limit && ./limit Stack start at 0x7fff51094ba8, end at 0x7fff4f094ba8. If the pointer returned by alloca(3C) is within those memory addresses, and does not exceed the bottom (in this example, $7fff4f094ba8), it is safe to use.