USERSTACK          89 kernel/exec.c    if((sz1 = uvmalloc(pagetable, sz, sz + (USERSTACK+1)*PGSIZE, PTE_W)) == 0)
USERSTACK          92 kernel/exec.c    uvmclear(pagetable, sz-(USERSTACK+1)*PGSIZE);
USERSTACK          94 kernel/exec.c    stackbase = sp - USERSTACK*PGSIZE;
USERSTACK        2416 user/usertests.c     sp -= USERSTACK*PGSIZE;