>everthing seems to compile, and I am left with an executable (?)
>file hello. However, trying to run this program gives the error

>**** EXEC FUNCTION FAILED; subsys =517; info = 48
>ABORT: /MMSTST/MK/foodir/hello
>NM SYS   a.00a9d288 dbg_abort_trace+$24
>NM UNKN  15c.0033bf6c
>NM UNKN  814.0004bbd8
>[1] + Done (134) ./hello

First trick: run the program one more time, but from MPE and not the
shell. This will make the error explanation more lucid. You can do this
from within the shell as in:

/MMSTST/MK/foodir> callci "run ./hello"
                   ^^^^^^^^^^^^^^^^^^^^

The resulting messages should either indicate a permissions problem or
missing externals. If it is the latter, make sure that /lib/libc.a in
fact exists. If not that, post the results of your run command (I
suspect other lurkers out there might be interested in POSIX as well)
and I'll comment then. You've done everything else correctly from what I
can see.