Unusual (?) problem with cd in ksh

[carroll at s.cs.uiuc.edu]

This is a problem with ksh-i. I fixed this a years or two ago, so my memory
is a little shaky (I don't do sysadm'ing anymore, so I don't have access
to the source anymore).

There is a procedure called "comsubst" which does command substitution, which
gets called during evaluation of `stuff`. It returns a pointer to a structure
that describes the result. The bug is that when comsubst is called on
the empty string (``), it returns a NULL pointer, which the routine which
calls it doesn't check for - it just immediately de-references it. What
happens then depends on the machine architecture. On the 3b family, location
0 is system memory but readable, so it just gets garbage, (always the same
garbage), which ends up not doing anything (acceptable). On other systems
(e.g., Sun's) location 0 is either not mapped or un-readable, so the
dereference causes a core dump. The solution we came up with was to put
a hack into comsubst that checked for the empty string, and changed it to
":" (a ksh-command that does nothing). I have no idea if this has been fixed
in ksh-88 or not. I will try to persuade the current sysadmins to let me
look and see what the fix was (we wrote all the details down when we fixed
it). You can try email to them at bogia at m.cs.uiuc.edu or walquist at m.cs.uiuc.edu

P.S. I sent Mr. Krell some email about this, but it must have sounded very
incoherent - sorry about that.

Alan M. Carroll                "And there you are
carroll at s.cs.uiuc.edu           Saying 'We have the Moon, so now the Stars...'"
CS Grad / U of Ill @ Urbana    ...{ucbvax,pur-ee,convex}!s.cs.uiuc.edu!carroll