linux-kernel - Re: [PATCH] drm/msm: Fix return type of mdp4_lvds_connector_mode

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Date:   Mon, 31 Oct 2022 15:10:54 -0700
From:   Nathan Chancellor <nathan@...nel.org>
To:     Nathan Huckleberry <nhuck@...gle.com>
Cc:     Dan Carpenter <error27@...il.com>, llvm@...ts.linux.dev,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Tom Rix <trix@...hat.com>, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/msm: Fix return type of
 mdp4_lvds_connector_mode_valid

Hi all,

On Tue, Sep 13, 2022 at 01:55:48PM -0700, Nathan Huckleberry wrote:
> The mode_valid field in drm_connector_helper_funcs is expected to be of
> type:
> enum drm_mode_status (* mode_valid) (struct drm_connector *connector,
>                                      struct drm_display_mode *mode);
> 
> The mismatched return type breaks forward edge kCFI since the underlying
> function definition does not match the function hook definition.
> 
> The return type of mdp4_lvds_connector_mode_valid should be changed from
> int to enum drm_mode_status.
> 
> Reported-by: Dan Carpenter <error27@...il.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
> Cc: llvm@...ts.linux.dev
> Signed-off-by: Nathan Huckleberry <nhuck@...gle.com>
> ---
>  drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c b/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
> index 7288041dd86a..7444b75c4215 100644
> --- a/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
> +++ b/drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c
> @@ -56,8 +56,9 @@ static int mdp4_lvds_connector_get_modes(struct drm_connector *connector)
>  	return ret;
>  }
>  
> -static int mdp4_lvds_connector_mode_valid(struct drm_connector *connector,
> -				 struct drm_display_mode *mode)
> +static enum drm_mode_status
> +mdp4_lvds_connector_mode_valid(struct drm_connector *connector,
> +			       struct drm_display_mode *mode)
>  {
>  	struct mdp4_lvds_connector *mdp4_lvds_connector =
>  			to_mdp4_lvds_connector(connector);
> -- 
> 2.37.2.789.g6183377224-goog
> 
> 

Did this patch get lost somewhere? I do not see it picked up. It is
needed to avoid a new WIP warning from clang for catching these CFI
failures:

drivers/gpu/drm/msm/disp/mdp4/mdp4_lvds_connector.c:89:16: error: incompatible function pointer types initializing 'enum drm_mode_status (*)(struct drm_connector *, struct drm_display_mode *)' with an expression of type 'int (struct drm_connector *, struct drm_display_mode *)' [-Werror,-Wincompatible-function-pointer-types-strict]
        .mode_valid = mdp4_lvds_connector_mode_valid,
                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Cheers,
Nathan