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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Tue, 27 Apr 2021 17:26:53 -0700
Message-ID: <CAHk-=whZN6zfnOTYmrUvur-+Mw8UOBpQxuhCJQ-R7J9zwsGwBA@mail.gmail.com>
Subject: Re: New warnings with gcc-11
To:     Dave Airlie <airlied@gmail.com>,
        Jani Nikula <jani.nikula@intel.com>,
        Joonas Lahtinen <joonas.lahtinen@linux.intel.com>,
        =?UTF-8?B?VmlsbGUgU3lyasOkbMOk?= <ville.syrjala@linux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc:     Daniel Vetter <daniel.vetter@ffwll.ch>,
        dri-devel <dri-devel@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Tue, Apr 27, 2021 at 4:43 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> I think I will make the argument type to intel_print_wm_latency() be
> just "const u16 wm[]" for now, just to avoid seeing a ton of silly
> warnings.

After fixing the trivial ones, this one remains:

  drivers/gpu/drm/i915/display/intel_dp.c: In function
=E2=80=98intel_dp_check_mst_status=E2=80=99:
  drivers/gpu/drm/i915/display/intel_dp.c:4554:22: warning:
=E2=80=98drm_dp_channel_eq_ok=E2=80=99 reading 6 bytes from a region of siz=
e 4
[-Wstringop-overread]
   4554 |                     !drm_dp_channel_eq_ok(&esi[10],
intel_dp->lane_count)) {
        |
^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  drivers/gpu/drm/i915/display/intel_dp.c:4554:22: note: referencing
argument 1 of type =E2=80=98const u8 *=E2=80=99 {aka =E2=80=98const unsigne=
d char *=E2=80=99}
  In file included from drivers/gpu/drm/i915/display/intel_dp.c:38:
  ./include/drm/drm_dp_helper.h:1459:6: note: in a call to function
=E2=80=98drm_dp_channel_eq_ok=E2=80=99
   1459 | bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZ=
E],
        |      ^~~~~~~~~~~~~~~~~~~~

and I'm not fixing that one, because it actually looks like a valid
warning, and doesn't have an obvious fix.

That "esi[]" array is 14 bytes in size (DP_DPRX_ESI_LEN). So when it
does that "&esi[10]" and passes it in as an argument, then only 4
bytes remain of the array.

And drm_dp_channel_eq_ok() supposedly takes a "const u8
link_status[DP_LINK_STATUS_SIZE]", which is 6 bytes.

There may be some reason this is ok, but it does look a bit fishy, and
the compiler warning is appropriate.

            Linus