Re: [Outreachy kernel] Coccinelle: understanding its output

["Fabio M. De Francesco" <fmdefrancesco@gmail.com>]

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