usr/src/libc/sys/mcount.s

# count subroutine called during profiling

.globl  mcount
.comm   countbase,4

mcount:
        movl    (r0),r1
        beql    init
incr:
        incl    (r1)
return:
        rsb
init:
        movl    countbase,r1
        beql    return
        addl2   $8,countbase
        movl    (sp),(r1)+
        movl    r1,(r0)
        brb     incr