Re: [PATCH][next] drm/amd/pm: Replace one-element array with flexible-array in struct SISLANDS_SMC_SWSTATE

[Alex Deucher]

On Wed, Feb 10, 2021 at 5:40 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].
>
> Refactor the code according to the use of a flexible-array member in
> struct SISLANDS_SMC_SWSTATE, instead of a one-element array, and use
> the struct_size() helper to calculate the size for the allocation.
>
> Also, this helps with the ongoing efforts to enable -Warray-bounds and
> fix the following warnings:
>
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:2448:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:2449:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:2450:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:2451:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:2452:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
> drivers/gpu/drm/amd/amdgpu/../pm/powerplay/si_dpm.c:5570:20: warning: array
> subscript 1 is above array bounds of ‘SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’
> {aka ‘struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL[1]’} [-Warray-bounds]
>
> [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/6023be58.sk66L%2FV4vuSJI5mI%25lkp@xxxxxxxxx/
> Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>

Applied.  Thanks!

Alex


> ---
>  drivers/gpu/drm/amd/pm/powerplay/si_dpm.c       |  6 ++----
>  drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h | 10 +++++-----
>  2 files changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/pm/powerplay/si_dpm.c b/drivers/gpu/drm/amd/pm/powerplay/si_dpm.c
> index afa1711c9620..62291358fb1c 100644
> --- a/drivers/gpu/drm/amd/pm/powerplay/si_dpm.c
> +++ b/drivers/gpu/drm/amd/pm/powerplay/si_dpm.c
> @@ -5715,11 +5715,9 @@ static int si_upload_sw_state(struct amdgpu_device *adev,
>         int ret;
>         u32 address = si_pi->state_table_start +
>                 offsetof(SISLANDS_SMC_STATETABLE, driverState);
> -       u32 state_size = sizeof(SISLANDS_SMC_SWSTATE) +
> -               ((new_state->performance_level_count - 1) *
> -                sizeof(SISLANDS_SMC_HW_PERFORMANCE_LEVEL));
>         SISLANDS_SMC_SWSTATE *smc_state = &si_pi->smc_statetable.driverState;
> -
> +       size_t state_size = struct_size(smc_state, levels,
> +                                       new_state->performance_level_count);
>         memset(smc_state, 0, state_size);
>
>         ret = si_convert_power_state_to_smc(adev, amdgpu_new_state, smc_state);
> diff --git a/drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h b/drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h
> index d2930eceaf3c..0f7554052c90 100644
> --- a/drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h
> +++ b/drivers/gpu/drm/amd/pm/powerplay/sislands_smc.h
> @@ -182,11 +182,11 @@ typedef struct SISLANDS_SMC_HW_PERFORMANCE_LEVEL SISLANDS_SMC_HW_PERFORMANCE_LEV
>
>  struct SISLANDS_SMC_SWSTATE
>  {
> -    uint8_t                             flags;
> -    uint8_t                             levelCount;
> -    uint8_t                             padding2;
> -    uint8_t                             padding3;
> -    SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[1];
> +       uint8_t                             flags;
> +       uint8_t                             levelCount;
> +       uint8_t                             padding2;
> +       uint8_t                             padding3;
> +       SISLANDS_SMC_HW_PERFORMANCE_LEVEL   levels[];
>  };
>
>  typedef struct SISLANDS_SMC_SWSTATE SISLANDS_SMC_SWSTATE;
> --
> 2.27.0
>
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