linux-kernel - Re: [PATCH] drm/amdgpu: fix warning for overflow check

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Date:   Mon, 27 Sep 2021 15:07:13 +0200
From:   Christian König <christian.koenig@....com>
To:     Arnd Bergmann <arnd@...nel.org>,
        Alex Deucher <alexander.deucher@....com>,
        "Pan, Xinhui" <Xinhui.Pan@....com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Chunming Zhou <david1.zhou@....com>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] drm/amdgpu: fix warning for overflow check

Am 27.09.21 um 14:58 schrieb Arnd Bergmann:
> From: Arnd Bergmann <arnd@...db.de>
>
> The overflow check in amdgpu_bo_list_create() causes a warning with
> clang-14 on 64-bit architectures, since the limit can never be
> exceeded.
>
> drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c:74:18: error: result of comparison of constant 256204778801521549 with expression of type 'unsigned int' is always false [-Werror,-Wtautological-constant-out-of-range-compare]
>          if (num_entries > (SIZE_MAX - sizeof(struct amdgpu_bo_list))
>              ~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
> The check remains useful for 32-bit architectures, so just avoid the
> warning by using size_t as the type for the count.
>
> Fixes: 920990cb080a ("drm/amdgpu: allocate the bo_list array after the list")
> Signed-off-by: Arnd Bergmann <arnd@...db.de>

Reviewed-by: Christian König <christian.koenig@....com>

> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c | 2 +-
>   drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> index 15c45b2a3983..714178f1b6c6 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.c
> @@ -61,7 +61,7 @@ static void amdgpu_bo_list_free(struct kref *ref)
>   
>   int amdgpu_bo_list_create(struct amdgpu_device *adev, struct drm_file *filp,
>   			  struct drm_amdgpu_bo_list_entry *info,
> -			  unsigned num_entries, struct amdgpu_bo_list **result)
> +			  size_t num_entries, struct amdgpu_bo_list **result)
>   {
>   	unsigned last_entry = 0, first_userptr = num_entries;
>   	struct amdgpu_bo_list_entry *array;
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
> index c905a4cfc173..044b41f0bfd9 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_bo_list.h
> @@ -61,7 +61,7 @@ int amdgpu_bo_create_list_entry_array(struct drm_amdgpu_bo_list_in *in,
>   int amdgpu_bo_list_create(struct amdgpu_device *adev,
>   				 struct drm_file *filp,
>   				 struct drm_amdgpu_bo_list_entry *info,
> -				 unsigned num_entries,
> +				 size_t num_entries,
>   				 struct amdgpu_bo_list **list);
>   
>   static inline struct amdgpu_bo_list_entry *