usr/src/libc/sys/crt0.s

# C runtime startoff

        .set    exit,1
.globl  _exit
.globl  start
.globl  _main
.globl  _environ

#
#       C language startup routine

start:
        .word   0x0000
        subl2   $8,sp
        movl    8(sp),(sp)  #  argc
        movab   12(sp),r0
        movl    r0,4(sp)  #  argv
L1:
        tstl    (r0)+  #  null args term ?
        bneq    L1
        cmpl    r0,*4(sp)  #  end of 'env' or 'argv' ?
        blss    L2
        tstl    -(r0)  # envp's are in list
L2:
        movl    r0,8(sp)  #  env
        movl    r0,_environ  #  indir is 0 if no env ; not 0 if env
        calls   $3,_main
        pushl   r0
        calls   $1,_exit
        chmk    $exit
#
        .data
_environ:       .space  4