Re: [cocci] coccinelle: How to remove a return at the end of a void function?

["Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>]

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Hello Julia,

On Mon, Dec 26, 2022 at 05:02:35PM +0100, Julia Lawall wrote:
> On Sun, 25 Dec 2022, Uwe Kleine-König wrote:
> 
> > Hello Julia,
> >
> > first of all thanks for your quick answer.
> >
> > On Sat, Dec 24, 2022 at 01:28:04PM +0100, Julia Lawall wrote:
> > > On Sat, 24 Dec 2022, Uwe Kleine-König wrote:
> > > > A simplified spatch looks as follows:
> > > >
> > > > -------->8--------
> > > > virtual patch
> > > >
> > > > @p1@
> > > > identifier pdev;
> > > > @@
> > > > -int
> > > > +void
> > > >  rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
> > > >  <...
> > > > -return 0;
> > > > +return;
> > > >  ...>
> > > >  }
> > > > -------->8--------
> > > >
> > > > This results in:
> > > >
> > > > -------->8--------
> > > > diff -u -p a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c
> > > > --- a/drivers/mmc/host/rtsx_usb_sdmmc.c
> > > > +++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
> > > > @@ -1379,13 +1379,13 @@ static int rtsx_usb_sdmmc_drv_probe(stru
> > > >         return 0;
> > > >  }
> > > >
> > > > -static int rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
> > > > +static void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
> > > >  {
> > > >         struct rtsx_usb_sdmmc *host = platform_get_drvdata(pdev);
> > > >         struct mmc_host *mmc;
> > > >
> > > >         if (!host)
> > > > -               return 0;
> > > > +               return;
> > > >
> > > >         mmc = host->mmc;
> > > >         host->host_removal = true;
> > > > @@ -1416,7 +1416,7 @@ static int rtsx_usb_sdmmc_drv_remove(str
> > > >         dev_dbg(&(pdev->dev),
> > > >                 ": Realtek USB SD/MMC module has been removed\n");
> > > >
> > > > -       return 0;
> > > > +       return;
> > > >  }
> > > >
> > > >  #ifdef CONFIG_PM
> > > > -------->8--------
> > > >
> > > > which is as intended. Now I want to remove the useless "return;" at the
> > > > end of the function, however adding
> > > >
> > > > -------->8--------
> > > > @p2 depends on p1@
> > > > identifier pdev;
> > > > @@
> > > >  void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
> > > >  ...
> > > > -return;
> > > >  }
> > > > -------->8--------
> > > >
> > > > to the spatch doesn't (only) do the intended:
> > >
> > > The problem is that Coccinelle is following the control-flow through the
> > > function, and all of the returns are at the end of a control.flow path.
> > > The simple, hacky solution is to change the return;s into some function
> > > call Return();, then do like the above for Return(); and then change the
> > > Return();s back to return;s
> >
> > OK, I tried, but somehow coccinelle refuse to work after I introduced
> > Return(), even replacing them by return; doesn't work:
> >
> > -------->8--------
> > virtual patch
> >
> > @p1@
> > identifier pdev;
> > @@
> > -int
> > +void
> >  rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
> >  ...
> > -return 0;
> > +Return();
> >  ...
> >  }
> >
> > @p2@
> > identifier pdev;
> > @@
> >  void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
> >  ...
> > -Return();
> > +return;
> >  ...
> >  }
> 
> The problem is that a control-flow path at this point can have multiple
> calls to Return();  You pattern only matches when every control-flow path
> through the code has exactly one Return().

Ah, ok. This wasn't clear to me from reading the documentation (e.g.
https://coccinelle.gitlabpages.inria.fr/website/docs/main_grammar.html)
 
> You should have one rule that removes the final Return();
> 
>  @p2@
>  identifier pdev;
>  @@
>   void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
>   ...
>  -Return();
>   }
> 
> Then another rule to remove the others:
> 
>  @p2@
>  identifier pdev;
>  @@
>   void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
>   <...
>  -Return();
>  +return;
>   ...>
>   }

I now have

-------->8--------
virtual patch

@p1@
identifier pdev;
@@
-int
+void
 rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
 ...
-return 0;
+Return();
 ...
 }

@p2@
identifier pdev;
@@
 void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
 ...
-Return();
 }

@p3@
identifier pdev;
@@
 void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev) {
 <...
-Return();
+return;
 ...>
 }
-------->8--------

But there p2 suffers from the same problem and only matches
code paths with exactly 1 Return(). So the above results in

-------->8--------
diff -u -p a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c
--- a/drivers/mmc/host/rtsx_usb_sdmmc.c
+++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
@@ -1379,13 +1379,13 @@ static int rtsx_usb_sdmmc_drv_probe(stru
        return 0;
 }

-static int rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
+static void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
 {
        struct rtsx_usb_sdmmc *host = platform_get_drvdata(pdev);
        struct mmc_host *mmc;

        if (!host)
-               return 0;
+               return;

        mmc = host->mmc;
        host->host_removal = true;
@@ -1416,7 +1416,7 @@ static int rtsx_usb_sdmmc_drv_remove(str
        dev_dbg(&(pdev->dev),
                ": Realtek USB SD/MMC module has been removed\n");

-       return 0;
+       return;
 }

 #ifdef CONFIG_PM
-------->8--------

and only if I remove the "if (!host) return 0;" block before patch
generation, the final return is also dropped. 

I think this is good enough for me, as there are not too many cases like
the above. If there is spatch that does the desired change (i.e.

-------->8--------
diff -u -p a/drivers/mmc/host/rtsx_usb_sdmmc.c b/drivers/mmc/host/rtsx_usb_sdmmc.c
--- a/drivers/mmc/host/rtsx_usb_sdmmc.c
+++ b/drivers/mmc/host/rtsx_usb_sdmmc.c
@@ -1379,13 +1379,11 @@ static int rtsx_usb_sdmmc_drv_probe(stru
        return 0;
 }

-static int rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
+static void rtsx_usb_sdmmc_drv_remove(struct platform_device *pdev)
 {
        struct rtsx_usb_sdmmc *host = platform_get_drvdata(pdev);
        struct mmc_host *mmc;

        if (!host)
-               return 0;
+               return;

        mmc = host->mmc;
        host->host_removal = true;
@@ -1416,7 +1416,7 @@ static int rtsx_usb_sdmmc_drv_remove(str
        dev_dbg(&(pdev->dev),
                ": Realtek USB SD/MMC module has been removed\n");
-
-       return 0;
 }

 #ifdef CONFIG_PM
-------->8--------
) I'd be happy to hear and learn about it.

Thanks
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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