linux-kernel - Re: coccinelle: How to remove a return at the end of a void function?

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Date:   Sun, 25 Dec 2022 22:20:11 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Julia Lawall <julia.lawall@...ia.fr>
Cc:     kernel@...gutronix.de, Nicolas Palix <nicolas.palix@...g.fr>,
        linux-kernel@...r.kernel.org, cocci@...ia.fr
Subject: Re: coccinelle: How to remove a return at the end of a void function?

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;
 ...
 }
-------->8--------

results in

-------->8--------
$ /usr/bin/spatch --debug -D patch --very-quiet --cocci-file scripts/coccinelle/api/test.cocci --patch . --dir drivers/mmc/host/rtsx_usb_sdmmc.c -I ./arch/x86/include -I ./arch/x86/include/generated -I ./include -I ./arch/x86/include/uapi -I ./arch/x86/include/generated/uapi -I ./include/uapi -I ./include/generated/uapi --include ./include/linux/compiler-version.h --include ./include/linux/kconfig.h --jobs 4 --chunksize 1
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
@@ -1385,7 +1385,7 @@ static int rtsx_usb_sdmmc_drv_remove(str
 	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--------

Adding --debug doesn't give any hints.

(And if I add another hunk inbeetween removing Return at the end of the
function there is no effect either.)

Do I need to split that in two spatches to make coccinelle cooperate?

(If it matters, this is coccinelle as shipped by Debian, Version
1.1.1.deb-2)

Best regards
Uwe

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

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