4.1c Cshell bug? (actually an exec bug)

[dean at cornell.UUCP]

There is a bug in the exec routine in the 4.1c kernel.  One
manifestation of this bug is when the shell tries to execute a command
file that does not have "#! /bin/csh"  (or "#! /bin/sh") as its first
line.  The problem is that an incorrect error code is sometimes
returned, resulting in messages like "Bad file number".

There are two ways (at least) to fix this problem.  One is to make sure
that there is always an explicit shell specification at the beginning
of shell command files.  In this case the exec will always succeed, and
the shell program won't have to look at the returned error code.  The
other fix is to install the following code into /sys/sys/kern_process.c
and build and install a new system.  The code replaces that at the end
of the "execve" function from the label "bad:" to the end of the function.
-----------------------------------------------
bad:
        /* CORNELL DEBUG: claim there's a path */
        /* thru iput that clears u.u_error.    */

        { int sav_u_error;
            sav_u_error = u.u_error;
            u.u_error = 0;
            if (bp)
                brelse(bp);
            if (bno)
                rmfree(argmap, (long)ctod(clrnd((int) btoc(NCARGS))), bno);
            iput(ip);
            if( u.u_error == 0 )
                u.u_error = sav_u_error; 
        }
}
-----------------------------------------------

Berkeley is aware of the problem, and it will presumably be fixed in
later releases.
                                    Dean Krafft
                                    Cornell Computer Science Dept.
                                    (607) 256-4052
                                    uucp: decvax!cornell!dean
                                    ARPA: dean at cornell