exec()

[ron%brl-bmd at sri-unix.UUCP]

From:      Ron Natalie <ron at brl-bmd>

Depending on your version of UNIX, down near the end of exec will
code to set it after it zeros all the registers it will set u.u_ar0[R7]
to zero, so that when the system returns to user mode it will start
at zero.  In newer versions, the loop that clears the registers is
replaced with a call to setregs.  In the middle of set regs it sets
u.u_ar0[PC] to the starting address specified in the a.out header.

-Ron