Coccinelle: understanding its output

Coccinelle: understanding its output

[Fabio M. De Francesco]

I think that I don't yet understand Coccinelle's output. 

I've just run the following command:
spatch --sp-file scripts/coccinelle/free/kfree.cocci --dir drivers/staging/
wlan-ng/prism2fw.c

It outputs something that looks like a patch:

HANDLING: drivers/staging/wlan-ng/prism2fw.c
     (ONCE) already tagged but only removed, so safe
diff = 
--- drivers/staging/wlan-ng/prism2fw.c
+++ /tmp/cocci-output-17844-0c6c7c-prism2fw.c

First, what is /tmp/cocci-output-17844-0c6c7c-prism2fwc? It is not a file in /
tmp. If it is a file, where is it?

The output goes on with lines like the following ones:

  @@ -1008,8 +1005,6 @@ static int writeimage(struct wlandevice
        rstmsg = kzalloc(sizeof(*rstmsg), GFP_KERNEL);
        rwrmsg = kzalloc(sizeof(*rwrmsg), GFP_KERNEL);
        if (!rstmsg || !rwrmsg) {
-               kfree(rstmsg);
-               kfree(rwrmsg);
                netdev_err(wlandev->netdev,
                           "%s: no memory for firmware download, aborting 
download\n",
                           __func__);

Please read the two lines with a trailing '-'... Does Coccinelle mean that 
they should be removed? If yes, I'm not able to understand why, because I 
think they must not be removed. Am I wrong?

 I'd appreciate some help.

Thanks,

Fabio
 

Re: [Outreachy kernel] Coccinelle: understanding its output

[Julia Lawall]

On Mon, 19 Apr 2021, Fabio M. De Francesco wrote:

> I think that I don't yet understand Coccinelle's output.
>
> I've just run the following command:
> spatch --sp-file scripts/coccinelle/free/kfree.cocci --dir drivers/staging/
> wlan-ng/prism2fw.c
>
> It outputs something that looks like a patch:
>
> HANDLING: drivers/staging/wlan-ng/prism2fw.c
>      (ONCE) already tagged but only removed, so safe
> diff =
> --- drivers/staging/wlan-ng/prism2fw.c
> +++ /tmp/cocci-output-17844-0c6c7c-prism2fw.c
>
> First, what is /tmp/cocci-output-17844-0c6c7c-prism2fwc? It is not a file in /
> tmp. If it is a file, where is it?
>
> The output goes on with lines like the following ones:
>
>   @@ -1008,8 +1005,6 @@ static int writeimage(struct wlandevice
>         rstmsg = kzalloc(sizeof(*rstmsg), GFP_KERNEL);
>         rwrmsg = kzalloc(sizeof(*rwrmsg), GFP_KERNEL);
>         if (!rstmsg || !rwrmsg) {
> -               kfree(rstmsg);
> -               kfree(rwrmsg);
>                 netdev_err(wlandev->netdev,
>                            "%s: no memory for firmware download, aborting
> download\n",
>                            __func__);
>
> Please read the two lines with a trailing '-'... Does Coccinelle mean that
> they should be removed? If yes, I'm not able to understand why, because I
> think they must not be removed. Am I wrong?

Sorry.  I think that the *s are a left over from a version of the semantic
patch that was trying to do more.  The semantic patches in the Linux
kernel are meant to be used with make coccicheck, which would have avoided
this problem.  The key is the lines

virtual org
virtual report

near the top of the file.  This means that the semantic patch should only
be run with either the option -D org (producing emacs org mode) or the
option -D report (producing text).  Both of these modes suppress the -
that you are seeing.

The - comes from the uses of * in the semantic patch, that is used to
highlight lines of interest, where the highlighting is done by putting a -
at the beginning of the line.  It's not meant as a suggestion to remove
the line, just that you might want to look at it.  But in this case, as
you noted, there is nothing interesting to see.  I will remove the *s.

julia

Re: [Outreachy kernel] Coccinelle: understanding its output

[Fabio M. De Francesco]

On Monday, April 19, 2021 8:58:24 PM CEST Julia Lawall wrote:
> On Mon, 19 Apr 2021, Fabio M. De Francesco wrote:
> > I think that I don't yet understand Coccinelle's output.
> > 
> > I've just run the following command:
> > spatch --sp-file scripts/coccinelle/free/kfree.cocci --dir drivers/
staging/
> > wlan-ng/prism2fw.c
> > 
> > It outputs something that looks like a patch:
> > 
> > HANDLING: drivers/staging/wlan-ng/prism2fw.c
> > 
> >      (ONCE) already tagged but only removed, so safe
> > 
> > diff =
> > --- drivers/staging/wlan-ng/prism2fw.c
> > +++ /tmp/cocci-output-17844-0c6c7c-prism2fw.c
> > 
> > First, what is /tmp/cocci-output-17844-0c6c7c-prism2fwc? It is not a file 
in
> > / tmp. If it is a file, where is it?
> > 
> > The output goes on with lines like the following ones:
> >   @@ -1008,8 +1005,6 @@ static int writeimage(struct wlandevice
> >   
> >         rstmsg = kzalloc(sizeof(*rstmsg), GFP_KERNEL);
> >         rwrmsg = kzalloc(sizeof(*rwrmsg), GFP_KERNEL);
> >         if (!rstmsg || !rwrmsg) {
> > 
> > -               kfree(rstmsg);
> > -               kfree(rwrmsg);
> > 
> >                 netdev_err(wlandev->netdev,
> >                 
> >                            "%s: no memory for firmware download, aborting
> > 
> > download\n",
> > 
> >                            __func__);
> > 
> > Please read the two lines with a trailing '-'... Does Coccinelle mean that
> > they should be removed? If yes, I'm not able to understand why, because I
> > think they must not be removed. Am I wrong?
> 
> Sorry.  I think that the *s are a left over from a version of the semantic
> patch that was trying to do more.  The semantic patches in the Linux
> kernel are meant to be used with make coccicheck, which would have avoided
> this problem.  The key is the lines
>
"make coccicheck" fails with the following message:

Python error: No module named coccilib.elems
coccicheck failed
make: *** [Makefile:1937: coccicheck] Error 255
> 
> virtual org
> virtual report
> 
> near the top of the file.  This means that the semantic patch should only
> be run with either the option -D org (producing emacs org mode) or the
> option -D report (producing text).  Both of these modes suppress the -
> that you are seeing.
>
Run of "spatch -D report --sp-file scripts/coccinelle/api/kfree_mismatch.cocci 
--dir drivers/staging/" fails too:

init_defs_builtins: /usr/bin/../lib/coccinelle/standard.h
Python error: No module named coccilib.elems

I think that it depends on some package I have not yet installed, or to some 
environment variable that must be set for the Python interpreter to find the  
coccili.elems module... I really don't know.

Do you have any idea for solving this problem?

Thanks,

Fabio
> 
> The - comes from the uses of * in the semantic patch, that is used to
> highlight lines of interest, where the highlighting is done by putting a -
> at the beginning of the line.  It's not meant as a suggestion to remove
> the line, just that you might want to look at it.  But in this case, as
> you noted, there is nothing interesting to see.  I will remove the *s.
> 
> julia

Re: [Outreachy kernel] Coccinelle: understanding its output

[Julia Lawall]

On Tue, 20 Apr 2021, Fabio M. De Francesco wrote:

> On Monday, April 19, 2021 8:58:24 PM CEST Julia Lawall wrote:
> > On Mon, 19 Apr 2021, Fabio M. De Francesco wrote:
> > > I think that I don't yet understand Coccinelle's output.
> > >
> > > I've just run the following command:
> > > spatch --sp-file scripts/coccinelle/free/kfree.cocci --dir drivers/
> staging/
> > > wlan-ng/prism2fw.c
> > >
> > > It outputs something that looks like a patch:
> > >
> > > HANDLING: drivers/staging/wlan-ng/prism2fw.c
> > >
> > >      (ONCE) already tagged but only removed, so safe
> > >
> > > diff =
> > > --- drivers/staging/wlan-ng/prism2fw.c
> > > +++ /tmp/cocci-output-17844-0c6c7c-prism2fw.c
> > >
> > > First, what is /tmp/cocci-output-17844-0c6c7c-prism2fwc? It is not a file
> in
> > > / tmp. If it is a file, where is it?
> > >
> > > The output goes on with lines like the following ones:
> > >   @@ -1008,8 +1005,6 @@ static int writeimage(struct wlandevice
> > >
> > >         rstmsg = kzalloc(sizeof(*rstmsg), GFP_KERNEL);
> > >         rwrmsg = kzalloc(sizeof(*rwrmsg), GFP_KERNEL);
> > >         if (!rstmsg || !rwrmsg) {
> > >
> > > -               kfree(rstmsg);
> > > -               kfree(rwrmsg);
> > >
> > >                 netdev_err(wlandev->netdev,
> > >
> > >                            "%s: no memory for firmware download, aborting
> > >
> > > download\n",
> > >
> > >                            __func__);
> > >
> > > Please read the two lines with a trailing '-'... Does Coccinelle mean that
> > > they should be removed? If yes, I'm not able to understand why, because I
> > > think they must not be removed. Am I wrong?
> >
> > Sorry.  I think that the *s are a left over from a version of the semantic
> > patch that was trying to do more.  The semantic patches in the Linux
> > kernel are meant to be used with make coccicheck, which would have avoided
> > this problem.  The key is the lines
> >
> "make coccicheck" fails with the following message:
>
> Python error: No module named coccilib.elems
> coccicheck failed
> make: *** [Makefile:1937: coccicheck] Error 255
> >
> > virtual org
> > virtual report
> >
> > near the top of the file.  This means that the semantic patch should only
> > be run with either the option -D org (producing emacs org mode) or the
> > option -D report (producing text).  Both of these modes suppress the -
> > that you are seeing.
> >
> Run of "spatch -D report --sp-file scripts/coccinelle/api/kfree_mismatch.cocci
> --dir drivers/staging/" fails too:
>
> init_defs_builtins: /usr/bin/../lib/coccinelle/standard.h
> Python error: No module named coccilib.elems
>
> I think that it depends on some package I have not yet installed, or to some
> environment variable that must be set for the Python interpreter to find the
> coccili.elems module... I really don't know.
>
> Do you have any idea for solving this problem?

How did you install Coccinelle?

julia

Re: [Outreachy kernel] Coccinelle: understanding its output

[Fabio M. De Francesco]

On Tuesday, April 20, 2021 6:37:35 PM CEST Julia Lawall wrote:
> On Tue, 20 Apr 2021, Fabio M. De Francesco wrote:
> > On Monday, April 19, 2021 8:58:24 PM CEST Julia Lawall wrote:
> > > On Mon, 19 Apr 2021, Fabio M. De Francesco wrote:
> > > > I think that I don't yet understand Coccinelle's output.
> > > > 
> > > > I've just run the following command:
> > > > spatch --sp-file scripts/coccinelle/free/kfree.cocci --dir drivers/
> > 
> > staging/
> > 
> > > > wlan-ng/prism2fw.c
> > > > 
> > > > It outputs something that looks like a patch:
> > > > 
> > > > HANDLING: drivers/staging/wlan-ng/prism2fw.c
> > > > 
> > > >      (ONCE) already tagged but only removed, so safe
> > > > 
> > > > diff =
> > > > --- drivers/staging/wlan-ng/prism2fw.c
> > > > +++ /tmp/cocci-output-17844-0c6c7c-prism2fw.c
> > > > 
> > > > First, what is /tmp/cocci-output-17844-0c6c7c-prism2fwc? It is not a
> > > > file
> > 
> > in
> > 
> > > > / tmp. If it is a file, where is it?
> > > > 
> > > > The output goes on with lines like the following ones:
> > > >   @@ -1008,8 +1005,6 @@ static int writeimage(struct wlandevice
> > > >   
> > > >         rstmsg = kzalloc(sizeof(*rstmsg), GFP_KERNEL);
> > > >         rwrmsg = kzalloc(sizeof(*rwrmsg), GFP_KERNEL);
> > > >         if (!rstmsg || !rwrmsg) {
> > > > 
> > > > -               kfree(rstmsg);
> > > > -               kfree(rwrmsg);
> > > > 
> > > >                 netdev_err(wlandev->netdev,
> > > >                 
> > > >                            "%s: no memory for firmware download,
> > > >                            aborting
> > > > 
> > > > download\n",
> > > > 
> > > >                            __func__);
> > > > 
> > > > Please read the two lines with a trailing '-'... Does Coccinelle mean
> > > > that
> > > > they should be removed? If yes, I'm not able to understand why, 
because
> > > > I
> > > > think they must not be removed. Am I wrong?
> > > 
> > > Sorry.  I think that the *s are a left over from a version of the 
semantic
> > > patch that was trying to do more.  The semantic patches in the Linux
> > > kernel are meant to be used with make coccicheck, which would have 
avoided
> > > this problem.  The key is the lines
> > 
> > "make coccicheck" fails with the following message:
> > 
> > Python error: No module named coccilib.elems
> > coccicheck failed
> > make: *** [Makefile:1937: coccicheck] Error 255
> > 
> > > virtual org
> > > virtual report
> > > 
> > > near the top of the file.  This means that the semantic patch should 
only
> > > be run with either the option -D org (producing emacs org mode) or the
> > > option -D report (producing text).  Both of these modes suppress the -
> > > that you are seeing.
> > 
> > Run of "spatch -D report --sp-file
> > scripts/coccinelle/api/kfree_mismatch.cocci --dir drivers/staging/" fails
> > too:
> > 
> > init_defs_builtins: /usr/bin/../lib/coccinelle/standard.h
> > Python error: No module named coccilib.elems
> > 
> > I think that it depends on some package I have not yet installed, or to 
some
> > environment variable that must be set for the Python interpreter to find 
the
> > coccili.elems module... I really don't know.
> > 
> > Do you have any idea for solving this problem?
> 
> How did you install Coccinelle?
> 
> julia
>
My laptop runs openSuSE Tumbleweed. Therefore I installed Coccinelle with a 
simple "zypper install coccinelle". I see that it is (properly?) installed and 
that also coccigrep has been installed, even though I didn't ask explicitly 
for it.

Perhaps it would be better to reinstall Coccinelle from sources. I read on a 
Vaishali Thakkar series of slides that they are clonable from github.com/
coccinelle/coccinelle. I hope that I also find there some documentation that  
guides me to installing prerequisites and configure the tool for integrating 
with Tumbleweed environment.

Is it a good solution?

Thanks,

Fabio