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From:   Nick Desaulniers <ndesaulniers@google.com>
Date:   Wed, 29 Jan 2020 13:45:23 -0800
Message-ID: <CAKwvOd=EvaSJFcpjh6gSRMrb=D5hwJHNR3wz6uEg3fmqmoGqfg@mail.gmail.com>
Subject: Re: [PATCH] drm: msm: Fix return type of dsi_mgr_connector_mode_valid
 for kCFI
To:     John Stultz <john.stultz@linaro.org>
Cc:     lkml <linux-kernel@vger.kernel.org>,
        Rob Clark <robdclark@gmail.com>, Sean Paul <sean@poorly.run>,
        Sami Tolvanen <samitolvanen@google.com>,
        Todd Kjos <tkjos@google.com>,
        Alistair Delva <adelva@google.com>,
        Amit Pundir <amit.pundir@linaro.org>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        freedreno@lists.freedesktop.org,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Wed, Jan 29, 2020 at 12:12 PM John Stultz <john.stultz@linaro.org> wrote:
>
> I was hitting kCFI crashes when building with clang, and after
> some digging finally narrowed it down to the
> dsi_mgr_connector_mode_valid() function being implemented as
> returning an int, instead of an enum drm_mode_status.
>
> This patch fixes it, and appeases the opaque word of the kCFI
> gods (seriously, clang inlining everything makes the kCFI
> backtraces only really rough estimates of where things went
> wrong).
>
> Thanks as always to Sami for his help narrowing this down.
>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Sean Paul <sean@poorly.run>
> Cc: Sami Tolvanen <samitolvanen@google.com>
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Alistair Delva <adelva@google.com>
> Cc: Amit Pundir <amit.pundir@linaro.org>
> Cc: Sumit Semwal <sumit.semwal@linaro.org>
> Cc: freedreno@lists.freedesktop.org
> Cc: clang-built-linux@googlegroups.com
> Signed-off-by: John Stultz <john.stultz@linaro.org>

John, thanks for fixing this. Our inliner is a point of pride
(inlining indirect function calls; you're welcome). ;)
Indeed, the function pointer member `mode_valid` in `struct
drm_connector_helper_funcs` in
include/drm/drm_modeset_helper_vtables.h returns an `enum
drm_mode_status`.

Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>

> ---
>  drivers/gpu/drm/msm/dsi/dsi_manager.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/msm/dsi/dsi_manager.c b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> index 271aa7bbca925..355a60b4a536f 100644
> --- a/drivers/gpu/drm/msm/dsi/dsi_manager.c
> +++ b/drivers/gpu/drm/msm/dsi/dsi_manager.c
> @@ -336,7 +336,7 @@ static int dsi_mgr_connector_get_modes(struct drm_connector *connector)
>         return num;
>  }
>
> -static int dsi_mgr_connector_mode_valid(struct drm_connector *connector,
> +static enum drm_mode_status dsi_mgr_connector_mode_valid(struct drm_connector *connector,
>                                 struct drm_display_mode *mode)
>  {
>         int id = dsi_mgr_connector_get_id(connector);
> --

-- 
Thanks,
~Nick Desaulniers