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

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Message-ID: <alpine.DEB.2.22.394.2212241326310.2711@hadrien>
Date:   Sat, 24 Dec 2022 13:28:04 +0100 (CET)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
cc:     Julia Lawall <Julia.Lawall@...ia.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>, cocci@...ia.fr,
        linux-kernel@...r.kernel.org, kernel@...gutronix.de
Subject: Re: coccinelle: How to remove a return at the end of a void
 function?



On Sat, 24 Dec 2022, Uwe Kleine-König wrote:

> Hello,
>
> I work on a patch set that eventually makes the function
> rtsx_usb_sdmmc_drv_remove() return void:
>
> 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

julia


>
> -------->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;
> +               {}
>
>         mmc = host->mmc;
>         host->host_removal = true;
> @@ -1415,8 +1415,6 @@ 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--------
>
> It's obvious to me, why coccinelle also removes the first return, but
> it's not obvious to me, how to prevent this and only drop the 2nd one.
>
> Do you have a hint for me?
>
> Thanks in advance and happy holidays,
> Uwe
>
>
> --
> Pengutronix e.K.                           | Uwe Kleine-König            |
> Industrial Linux Solutions                 | https://www.pengutronix.de/ |
>