TRAP UNIX v1     UNIX v2     UNIX v3     UNIX v4     UNIX v5     UNIX v6     UNIX v7
----------------------------------------------------------------------------------------------------------------
 0   rele        rele        rele        indir       indir       indir       indir
 1   exit        exit        exit        exit        exit        exit        exit
 2   fork        fork        fork        fork        fork        fork        fork
 3   read        read        read        read        read        read        read
 4   write       write       write       write       write       write       write
 5   open        open        open        open        open        open        open
 6   close       close       close       close       close       close       close
 7   wait        wait        wait        wait        wait        wait        wait
 8   create      create      create      create      creat       creat       creat
 9   link        link        link        link        link        link        link
10   unlink      unlink      unlink      unlink      unlink      unlink      unlink
11   exec        exec        exec        exec        exec        exec        exec
12   chdir       chdir       chdir       chdir       chdir       chdir       chdir
13   time        time        time        time        time        time        time
14   makdir      makdir      makdir      mknod       mknod       mknod       mknod
15   chmod       chmod       chmod       chmod       chmod       chmod       chmod
16   chown       chown       chown       chown       chown       chown       chown
17   break       break       break       break       sbrk        sbrk        sbrk
18   stat        stat        stat        stat        stat        stat        stat
19   seek        seek        seek        seek        seek        seek        lseek
20   tell        tell       (tell)       -           getpid      getpid      getpid      early tell broken
21   mount       mount       mount       mount       mount       mount       mount
22   umount      umount      umount      umount      umount      umount      umount
23   setuid      setuid      setuid      setuid      setuid      setuid      setuid
24   getuid      getuid      getuid      getuid      getuid      getuid      getuid
25   stime       stime       stime       stime       stime       stime       stime
26   quit        quit        quit        -           -           ptrace      ptrace      quit moved to signal
27   intr        intr        intr        -           -           -           -           intr moved to signal
28   fstat       fstat       fstat       fstat       fstat       fstat       fstat
29   cemt        cemt        cemt        -           -           -           pause       cemt moved to signal
30   smdate      mdate       mdate       -           smdate      smdate      utime
31   stty        stty        stty        stty        stty        stty        stty
32   gtty        gtty        gtty        gtty        gtty        gtty        gtty
33   ilgins      ilgins      ilgins      -           -           -           -           ilgins moved to signal
34   -           hog         nice        nice        nice        nice        nice
35   -           sleep       sleep       sleep       sleep       sleep       ftime
36   -           sync        sync        sync        sync        sync        sync
37   -           kill        kill        kill        kill        kill        kill
38   -           -           csw         csw         switch      switch      -
39   -           -           boot        -           -           -           setpgrp
40   -           -           fpe         -           -           -           tell        fpe moved to signal
41   -           -           dup         dup         dup         dup         dup2
42   -           -           pipe        pipe        pipe        pipe        pipe
43   -           -           time        times       times       times       times
44   -           -           -           -           prof        prof        profil
45   -           -           -           -           tiu         tui         -
46   -           -           -           setgid      setgid      setgid      setgid
47   -           -           -           getgid      getgid      getgid      getgid
48   -           -           -           signal      signal      signal      signal
49   -           -           -           -           -           -           (USG)
50   -           -           -           -           -           -           (USG)
51   -           -           -           -           -           -           acct
52   -           -           -           -           -           -           phys
53   -           -           -           -           -           -           lock
54   -           -           -           -           -           -           ioctl
55   -           -           -           -           -           -           (readwrite) (reboot)
56   -           -           -           -           -           -           mpxchan     (mpx)
57   -           -           -           -           -           -           (USG)
58   -           -           -           -           -           -           (USG)
59   -           -           -           -           -           -           exece       (setinf)
60   -           -           -           -           -           -           umask       (getinf)
61   -           -           -           -           -           -           chroot
62   -           -           -           -           -           -           -
63   -           -           -           -           -           -           -

a.out v1         v2          v3          v4          v5          v6          v7
0000 &o205  br .+14          &o407 br .+20 or &410 br .+22
0002 sz_text                 sz_text
0004 sz_symb                 sz_init
0006 sz_relo                 sz_uninit
0008 sz_data                 sz_symb
0010 sz_unused (zero)        entry
0012 start of text           unused
0014                         reloc
0016                         start of text
0020
0022

All calls modify R0. Some calls also modify R1.
Cy set on exit if error occured and R0=error, otherwise Cy clear.