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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Mon, 15 Feb 2021 13:59:38 -0500
Message-ID: <CADnq5_NjBspgusW73UNXb2sLiOtsKiAvXTby0zg+OiL1DuEXFA@mail.gmail.com>
Subject: Re: [PATCH][next] drm/radeon/nislands_smc.h: Replace one-element
 array with flexible-array member in struct NISLANDS_SMC_SWSTATE
To:     "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc:     Alex Deucher <alexander.deucher@amd.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        linux-hardening@vger.kernel.org,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        LKML <linux-kernel@vger.kernel.org>
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On Wed, Feb 10, 2021 at 6:49 PM Gustavo A. R. Silva
<gustavoars@kernel.org> wrote:
>
> There is a regular need in the kernel to provide a way to declare having
> a dynamically sized set of trailing elements in a structure. Kernel code
> should always use =E2=80=9Cflexible array members=E2=80=9D[1] for these c=
ases. The older
> style of one-element or zero-length arrays should no longer be used[2].
>
> Use flexible-array member in struct NISLANDS_SMC_SWSTATE, instead of
> one-element array.
>
> Also, this helps with the ongoing efforts to enable -Warray-bounds by
> fixing the following warnings:
>
> drivers/gpu/drm/radeon/ni_dpm.c: In function =E2=80=98ni_convert_power_st=
ate_to_smc=E2=80=99:
> drivers/gpu/drm/radeon/ni_dpm.c:2521:20: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2521 |   smc_state->levels[i].dpm2.MaxPS =3D
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2523:20: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2523 |   smc_state->levels[i].dpm2.NearTDPDec =3D NISLANDS_DPM2_NEAR_TDP=
_DEC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2524:20: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2524 |   smc_state->levels[i].dpm2.AboveSafeInc =3D NISLANDS_DPM2_ABOVE_=
SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2525:20: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2525 |   smc_state->levels[i].dpm2.BelowSafeInc =3D NISLANDS_DPM2_BELOW_=
SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2526:35: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2526 |   smc_state->levels[i].stateFlags |=3D
>       |                                   ^~
> drivers/gpu/drm/radeon/ni_dpm.c:2526:35: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2526 |   smc_state->levels[i].stateFlags |=3D
>       |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
>  2527 |    ((i !=3D (state->performance_level_count - 1)) && power_boost_=
limit) ?
>       |    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~=
~~~~~~
>  2528 |    PPSMC_STATEFLAG_POWERBOOST : 0;
>       |    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/radeon/ni_dpm.c:2442:20: warning: array subscript 1 is ab=
ove array bounds of =E2=80=98NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99 =
{aka =E2=80=98struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]=E2=80=99} [-Warra=
y-bounds]
>  2442 |   smc_state->levels[i + 1].aT =3D cpu_to_be32(a_t);
>
> [1] https://en.wikipedia.org/wiki/Flexible_array_member
> [2] https://www.kernel.org/doc/html/v5.9/process/deprecated.html#zero-len=
gth-and-one-element-arrays
>
> Link: https://github.com/KSPP/linux/issues/79
> Link: https://github.com/KSPP/linux/issues/109
> Build-tested-by: kernel test robot <lkp@intel.com>
> Link: https://lore.kernel.org/lkml/6023ed54.BfIY+9Uz81I6nq19%25lkp@intel.=
com/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>

Applied.  Thanks!

Alex

> ---
>  drivers/gpu/drm/radeon/nislands_smc.h | 10 +++++-----
>  1 file changed, 5 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/radeon/nislands_smc.h b/drivers/gpu/drm/rade=
on/nislands_smc.h
> index 3cf8fc0d83f4..7395cb6b3cac 100644
> --- a/drivers/gpu/drm/radeon/nislands_smc.h
> +++ b/drivers/gpu/drm/radeon/nislands_smc.h
> @@ -134,11 +134,11 @@ typedef struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL NI=
SLANDS_SMC_HW_PERFORMANCE_LEV
>
>  struct NISLANDS_SMC_SWSTATE
>  {
> -    uint8_t                             flags;
> -    uint8_t                             levelCount;
> -    uint8_t                             padding2;
> -    uint8_t                             padding3;
> -    NISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[1];
> +       uint8_t                             flags;
> +       uint8_t                             levelCount;
> +       uint8_t                             padding2;
> +       uint8_t                             padding3;
> +       NISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[];
>  };
>
>  typedef struct NISLANDS_SMC_SWSTATE NISLANDS_SMC_SWSTATE;
> --
> 2.27.0
>
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