Re: [PATCH][next] drm/radeon/nislands_smc.h: Replace one-element array with flexible-array member in struct NISLANDS_SMC_SWSTATE

[Alex Deucher]

On Wed, Feb 10, 2021 at 6:49 PM Gustavo A. R. Silva
<gustavoars@xxxxxxxxxx> 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 “flexible array members”[1] for these cases. 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 ‘ni_convert_power_state_to_smc’:
> drivers/gpu/drm/radeon/ni_dpm.c:2521:20: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2521 |   smc_state->levels[i].dpm2.MaxPS =
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2523:20: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2523 |   smc_state->levels[i].dpm2.NearTDPDec = NISLANDS_DPM2_NEAR_TDP_DEC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2524:20: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2524 |   smc_state->levels[i].dpm2.AboveSafeInc = NISLANDS_DPM2_ABOVE_SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2525:20: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2525 |   smc_state->levels[i].dpm2.BelowSafeInc = NISLANDS_DPM2_BELOW_SAFE_INC;
>       |   ~~~~~~~~~~~~~~~~~^~~
> drivers/gpu/drm/radeon/ni_dpm.c:2526:35: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2526 |   smc_state->levels[i].stateFlags |=
>       |                                   ^~
> drivers/gpu/drm/radeon/ni_dpm.c:2526:35: warning: array subscript 1 is above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2526 |   smc_state->levels[i].stateFlags |=
>       |   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~
>  2527 |    ((i != (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 above array bounds of ‘NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’ {aka ‘struct NISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>  2442 |   smc_state->levels[i + 1].aT = 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-length-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@xxxxxxxxx>
> Link: https://lore.kernel.org/lkml/6023ed54.BfIY+9Uz81I6nq19%25lkp@xxxxxxxxx/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

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/radeon/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 NISLANDS_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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