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Date:   Mon, 31 Oct 2022 15:24:30 -0700
From:   Nathan Chancellor <nathan@kernel.org>
To:     Nathan Huckleberry <nhuck@google.com>
Cc:     Dan Carpenter <error27@gmail.com>, llvm@lists.linux.dev,
        Hyun Kwon <hyun.kwon@xilinx.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        Michal Simek <michal.simek@xilinx.com>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, dri-devel@lists.freedesktop.org,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm: xlnx: Fix return type of
 zynqmp_dp_connector_mode_valid
Message-ID: <Y2BLHjC0q3rbIL0d@dev-arch.thelio-3990X>
References: <20220913205600.155172-1-nhuck@google.com>
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In-Reply-To: <20220913205600.155172-1-nhuck@google.com>
Precedence: bulk

Hi all,

On Tue, Sep 13, 2022 at 01:56:00PM -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 zynqmp_dp_connector_mode_valid should be changed from
> int to enum drm_mode_status.
> 
> Reported-by: Dan Carpenter <error27@gmail.com>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1703
> Cc: llvm@lists.linux.dev
> Signed-off-by: Nathan Huckleberry <nhuck@google.com>
> ---
>  drivers/gpu/drm/xlnx/zynqmp_dp.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/xlnx/zynqmp_dp.c b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> index d14612b34796..f571b08d23d3 100644
> --- a/drivers/gpu/drm/xlnx/zynqmp_dp.c
> +++ b/drivers/gpu/drm/xlnx/zynqmp_dp.c
> @@ -1352,8 +1352,9 @@ zynqmp_dp_connector_best_encoder(struct drm_connector *connector)
>  	return &dp->encoder;
>  }
>  
> -static int zynqmp_dp_connector_mode_valid(struct drm_connector *connector,
> -					  struct drm_display_mode *mode)
> +static enum drm_mode_status
> +zynqmp_dp_connector_mode_valid(struct drm_connector *connector,
> +			       struct drm_display_mode *mode)
>  {
>  	struct zynqmp_dp *dp = connector_to_dp(connector);
>  	u8 max_lanes = dp->link_config.max_lanes;
> -- 
> 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/xlnx/zynqmp_dp.c:1396:16: 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     = zynqmp_dp_connector_mode_valid,
                          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 error generated.

Cheers,
Nathan