linux-kernel - Re: [PATCH] drm/i915: Avoid bitwise vs logical OR warning in snb_wm_latency

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAKwvOdmSFP98Mc1u2b+=_Dux9eB_yumRvxOx7UTXuyXOYzG3uA@mail.gmail.com>
Date:   Thu, 14 Oct 2021 14:21:43 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <nathan@...nel.org>
Cc:     Jani Nikula <jani.nikula@...ux.intel.com>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
        Dávid Bolvanský <david.bolvansky@...il.com>
Subject: Re: [PATCH] drm/i915: Avoid bitwise vs logical OR warning in snb_wm_latency_quirk()

On Thu, Oct 14, 2021 at 2:19 PM Nathan Chancellor <nathan@...nel.org> wrote:
>
> A new warning in clang points out a place in this file where a bitwise
> OR is being used with boolean types:
>
> drivers/gpu/drm/i915/intel_pm.c:3066:12: warning: use of bitwise '|' with boolean operands [-Wbitwise-instead-of-logical]
>         changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12) |
>                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> This construct is intentional, as it allows every one of the calls to
> ilk_increase_wm_latency() to occur (instead of short circuiting with
> logical OR) while still caring about the result of each call.
>
> To make this clearer to the compiler, use the '|=' operator to assign
> the result of each ilk_increase_wm_latency() call to changed, which
> keeps the meaning of the code the same but makes it obvious that every
> one of these calls is expected to happen.
>
> Link: https://github.com/ClangBuiltLinux/linux/issues/1473
> Reported-by: Nick Desaulniers <ndesaulniers@...gle.com>

Thanks for the patch!
Suggested-by: Dávid Bolvanský <david.bolvansky@...il.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

> Signed-off-by: Nathan Chancellor <nathan@...nel.org>
> ---
>  drivers/gpu/drm/i915/intel_pm.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index f90fe39cf8ca..aaa3a0998e4c 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -3050,9 +3050,9 @@ static void snb_wm_latency_quirk(struct drm_i915_private *dev_priv)
>          * The BIOS provided WM memory latency values are often
>          * inadequate for high resolution displays. Adjust them.
>          */
> -       changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12) |
> -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latency, 12) |
> -               ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latency, 12);
> +       changed = ilk_increase_wm_latency(dev_priv, dev_priv->wm.pri_latency, 12);
> +       changed |= ilk_increase_wm_latency(dev_priv, dev_priv->wm.spr_latency, 12);
> +       changed |= ilk_increase_wm_latency(dev_priv, dev_priv->wm.cur_latency, 12);
>
>         if (!changed)
>                 return;
>
> base-commit: d73b17465d6da0a94bc0fcc86b150e1e923e8f71
> --
> 2.33.1.637.gf443b226ca
>


-- 
Thanks,
~Nick Desaulniers