[Cocci] checking and fixing comma operator in if condition

[Cocci] checking and fixing comma operator in if condition

[Nicholas Mc Guire]

Hi !

 The below spatch works for me - and finds the cases I was looking
 for in report mode. In patch mode it fixes some in a bad way though
 due to some additional "bugs" in the if statement like:

+++ b/gpu/drm/nouveau/nvkm/core/notify.c
@@ -136,14 +136,16 @@ nvkm_notify_init(struct nvkm_object *obj
 {
        unsigned long flags;
        int ret = -ENODEV;
-       if ((notify->event = event), event->refs) {
+       (notify->event = event);
+       if (event->refs) {
  
 The extra parenthesis is wrong inside the if but of course it is
 kind of "wronger" outside the if while still valid C-code. Other
 cases that are fixed in a questionable case are e.g.

--- a/gpu/drm/nouveau/nvkm/subdev/fb/ramgk104.c
+++ b/gpu/drm/nouveau/nvkm/subdev/fb/ramgk104.c
@@ -1168,7 +1168,8 @@ gk104_ram_prog_0(struct gk104_ram *ram,
        if (&cfg->head == &ram->cfg)
                return;

-       if (mask = 0, data = 0, ram->diff.rammap_11_0a_03fe) {
+       mask = 0, data = 0;
+       if (ram->diff.rammap_11_0a_03fe) {

 In futher cases it is not clear if the unconditional part really was
 intended to take effect outside the conditional code so it is not
 clear if the placement before the if () is technically correct (I
 think it is semantically equivalent though - so bug-preserving in
 those cases).

 So... is it then better not even to offer the patch mode in this case ?

 Finally as it seems that while this is a general no-go, in the current
 -stable sources it only affects files in drivers/gpu/drm/nouveau/, thus
 not sure if this makes much sense for mainline at all.


thx!
hofrat


/// Check for unconditional code "hiding" in an if condition
/// effectively that code is unconditionally executed before
/// reaching the actual branch statement - which just makes it
/// hard to read and thus is *always* wrong.
/// Some of the cases found also look buggy 
///
/// As of 4.19-rc3 all 50 cases look like they are found and fixed
/// correctly - but as this is in the nuveau driver only it might
/// well be that this only fits that specific pattern.
///
// Confidence: Low
// Copyright: (C) 2018 Nicholas Mc Guire, OSADL.  GPLv2.
// Comments:
// Options: --no-includes --include-headers

virtual patch
virtual report

@badif@
position p;
statement S;
expression E1,E2;
@@

  if at p (E1,E2) S

@script:python depends on report@
p << badif.p;
@@

msg = "unconditional code hiding in if condition" 
coccilib.report.print_report(p[0],msg)

@fixbadif depends on badif && patch@
position p=badif.p;
statement S;
expression E1=badif.E1,E2=badif.E2;
@@

+ E1;
  if@p (
- E1,
  E2) 
  S 

@script:python depends on patch@
p << fixbadif.p;
@@

msg = "unconditional code in if condition moved" 
coccilib.report.print_report(p[0],msg)

[Cocci] Checking patches for questionable comma expressions in if conditions

[SF Markus Elfring]

> The below spatch works for me - and finds the cases I was looking
> for in report mode.

This is nice.


> In patch mode it fixes some in a bad way though due to some additional "bugs"
> in the if statement like:
?
> -       if ((notify->event = event), event->refs) {
> +       (notify->event = event);
> +       if (event->refs) {

I am curious on how software development considerations will evolve further
for such generated patches.

Will the shown script for the semantic patch language need any more fine-tuning?

Would the following transformation variant result in desirable differences
(after the specification of extra parentheses)?


@badif@
position P;
statement S;
expression E1,E2;
@@
 if at P ((E1),E2) S

?

@fixbadif depends on patch && badif@
position badif.P;
statement S;
expression badif.E1,badif.E2;
@@
+E1;
 if at P (
-      (E1),
       E2)
      S


> -       if (mask = 0, data = 0, ram->diff.rammap_11_0a_03fe) {
> +       mask = 0, data = 0;
> +       if (ram->diff.rammap_11_0a_03fe) {
>
> In futher cases it is not clear if the unconditional part really was
> intended to take effect outside the conditional code so it is not
> clear if the placement before the if () is technically correct

How do you think about to convert such a development concern into a more
advanced source code search pattern?

Regards,
Markus

[Cocci] Checking patches for questionable comma expressions in if conditions

[Julia Lawall]

On Wed, 12 Sep 2018, SF Markus Elfring wrote:

> > The below spatch works for me - and finds the cases I was looking
> > for in report mode.
>
> This is nice.
>
>
> > In patch mode it fixes some in a bad way though due to some additional "bugs"
> > in the if statement like:
> ?
> > -       if ((notify->event = event), event->refs) {
> > +       (notify->event = event);
> > +       if (event->refs) {
>
> I am curious on how software development considerations will evolve further
> for such generated patches.
>
> Will the shown script for the semantic patch language need any more fine-tuning?
>
> Would the following transformation variant result in desirable differences
> (after the specification of extra parentheses)?
>
>
> @badif@
> position P;
> statement S;
> expression E1,E2;
> @@
>  if at P ((E1),E2) S
>
> ?
>
> @fixbadif depends on patch && badif@
> position badif.P;
> statement S;
> expression badif.E1,badif.E2;
> @@
> +E1;
>  if at P (
> -      (E1),
>        E2)
>       S

Alternatively, I suspect that one could just do

- (
  E
- )
  ;

Or the original rule could be

+E1;
 if (
- (E1),
  E2) S1 else S2

>
>
> > -       if (mask = 0, data = 0, ram->diff.rammap_11_0a_03fe) {
> > +       mask = 0, data = 0;
> > +       if (ram->diff.rammap_11_0a_03fe) {
> >
> > In futher cases it is not clear if the unconditional part really was
> > intended to take effect outside the conditional code so it is not
> > clear if the placement before the if () is technically correct

I'm not sure to understand the problem here.  You want to also change the
, on the added line to a semicolon?

julia