Re: [open-cobol-list] CVS Update 20061015

[Duilio Protti]

Hi,

The prerelease builds and run correctly here. However, in regard of bug
#1571083, I have found one more issue.

The bug is related to statements like PERFORM F WITH TEST BEFORE UNTIL P,
where, if P is true at the first time, F mustn't execute at all.
Currently, OpenCobol execute F once.

I.e. for the program:

       IDENTIFICATION DIVISION.
       PROGRAM-ID. WithTestBefore1.

       PROCEDURE DIVISION.
       MAIN.
           PERFORM SAY-HELLO
               WITH TEST BEFORE UNTIL 1 < 2.
       SAY-HELLO.
           DISPLAY 'Hello, world'.


"Hello, world" is displayed once.

The extra issue I have found, is that aside from the wrong control flow,
OpenCobol generate potentially dangerous code. For the previous program,
it generates (only relevant fragment showed):

  {
    while (1)
      {
        if ((cob_cmp_int (&c_9, 2) <  0))
          break;
        /* PERFORM SAY-HELLO THRU SAY-HELLO */
        if (unlikely(++frame_index >= COB_STACK_SIZE))
            cob_fatal_error (COB_FERROR_STACK);
        frame_stack[frame_index].perform_through = 7;
        frame_stack[frame_index].return_address = &&l_10;
        goto l_7;
        l_10:
        frame_index--;
      }
  }

  /* SAY-HELLO: */
  l_7:;
  /* withtestbefore1.cob:9: DISPLAY */
  {
    cob_new_display (0, 1, 1, &c_12);
  }
  if (frame_stack[frame_index].perform_through == 7)
    goto *frame_stack[frame_index].return_address;

  cob_current_module = cob_current_module->next;
  return (*(int *) (b_2));


This is clearly dangerous: if test 'if ((cob_cmp_int (&c_9, 2) <  0))' is
true at the first iteration of the loop, control reach l_7: and then the
condition 'if (frame_stack[frame_index].perform_through == 7)' is
performed with 'perform_through' and 'return_address' fields
non-initialized.

If the garbage in 'perform_through' is by change equal to 7, then a goto
to (non-initialized) 'return_address' is performed, which in general will
result in a segfault (and the worst kind of bug, a random one).


Regards,
Duilio Protti.

> CVS updated.
> Tarball (AKA Prerelease) at :
> http://ww.sim-basis.de/open-cobol-0.33.tar.gz
>
> Too many things changed to list here.
> See the ChangeLog files in the top-level
> and sub-directories (cobc, libcob, config, bin, tests)
>
> Roger