I think setenv() will use malloc() (it might use mutexes), same for error printing if it uses printf() or perror(). Also, this is all mess if fork() is called

I think setenv() will use malloc() (it might use mutexes), same for error printing if it uses printf() or perror(). Also, this is all mess if fork() is called from a multi-threaded context. Esp. via clone(), which up to certain glibc() version cached getpid() result, and returned parent'd PID in the child (for performance reasons of course ;).