I pushed some new code and it's pretty cool.
This is some kernel code from drivers/char/ppdev.c
681 compat_negot = 0;
682 if (!(pp->flags & PP_CLAIMED) && pp->pdev &&
683 (pp->state.mode != IEEE1284_MODE_COMPAT)) {
684 struct ieee1284_info *info;
685
686 /* parport released, but not in compatibility mode */
687 parport_claim_or_block (pp->pdev);
688 pp->flags |= PP_CLAIMED;
689 info = &pp->pdev->port->ieee1284;
690 pp->saved_state.mode = info->mode;
691 pp->saved_state.phase = info->phase;
692 info->mode = pp->state.mode;
693 info->phase = pp->state.phase;
694 compat_negot = 1;
695 } else if ((pp->flags & PP_CLAIMED) && pp->pdev &&
696 (pp->pdev->port->ieee1284.mode != IEEE1284_MODE_COMPAT)) {
697 compat_negot = 2;
698 }
699 if (compat_negot) {
700 parport_negotiate (pp->pdev->port, IEEE1284_MODE_COMPAT);
701 printk (KERN_DEBUG CHRDEV
702 "%x: negotiated back to compatibility mode because "
703 "user-space forgot\n", minor);
704 }
705
706 if (pp->flags & PP_CLAIMED) {
707 struct ieee1284_info *info;
708
709 info = &pp->pdev->port->ieee1284;
The new smatch code recognizes that pp->pdev might be null when we
dereference it on line 709. It used to do that before as well... The
cool part is that it recognizes that dereferencing pp->dev on line 700 is
not a bug.
The trick is that when code paths get merged, all the states that are
unique to one side get saved in an "implied pool". The smatch_extra.c
code tracks very simple assignments like "compat_negot = 2".
When there is an "if (compat_negot)" condition, we make a list of both the
implied pools where compat_negot is not zero. All the states which are
two in both pools are true on line 700. So if compat_negot isn't zero,
pp->dev isn't null.
The sad part is that there are still way way too many false positives for
smatch to be practical... I need to rewrite smatch_extra to track many
more things. Also the checking scripts are pretty rubbish.
Nevertheless progress is being made...
regards,
dan carpenter
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