linux-kernel - Re: New warnings with gcc-11

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Date:   Tue, 27 Apr 2021 17:26:53 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Dave Airlie <airlied@...il.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: New warnings with gcc-11

On Tue, Apr 27, 2021 at 4:43 PM Linus Torvalds
<torvalds@...ux-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
‘intel_dp_check_mst_status’:
  drivers/gpu/drm/i915/display/intel_dp.c:4554:22: warning:
‘drm_dp_channel_eq_ok’ reading 6 bytes from a region of size 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 ‘const u8 *’ {aka ‘const unsigned char *’}
  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
‘drm_dp_channel_eq_ok’
   1459 | bool drm_dp_channel_eq_ok(const u8 link_status[DP_LINK_STATUS_SIZE],
        |      ^~~~~~~~~~~~~~~~~~~~

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