linux-kernel - Re: [PATCH] drm/amdgpu: Initialize shadow to false in gfx_v9_0_rlcg

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Date:   Wed, 18 Mar 2020 13:11:00 -0700
From:   Nick Desaulniers <ndesaulniers@...gle.com>
To:     Nathan Chancellor <natechancellor@...il.com>
Cc:     Alex Deucher <alexander.deucher@....com>,
        Christian König <christian.koenig@....com>,
        "David (ChunMing) Zhou" <David1.Zhou@....com>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Subject: Re: [PATCH] drm/amdgpu: Initialize shadow to false in gfx_v9_0_rlcg_wreg

On Tue, Mar 17, 2020 at 5:25 PM Nathan Chancellor
<natechancellor@...il.com> wrote:
>
> clang warns:
>
> drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c:754:6: warning: variable 'shadow'
> is used uninitialized whenever 'if' condition is
> false [-Wsometimes-uninitialized]
>         if (offset == grbm_cntl || offset == grbm_idx)
>             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c:757:6: note: uninitialized use
> occurs here
>         if (shadow) {
>             ^~~~~~
> drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c:754:2: note: remove the 'if' if
> its condition is always true
>         if (offset == grbm_cntl || offset == grbm_idx)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c:738:13: note: initialize the
> variable 'shadow' to silence this warning
>         bool shadow;
>                    ^
>                     = 0
> 1 warning generated.
>
> It is not wrong so initialize shadow to false to ensure shadow is always
> used initialized.

Yep, thanks for the patch.
Reviewed-by: Nick Desaulniers <ndesaulniers@...gle.com>

>
> Fixes: 2e0cc4d48b91 ("drm/amdgpu: revise RLCG access path")
> Link: https://github.com/ClangBuiltLinux/linux/issues/936
> Signed-off-by: Nathan Chancellor <natechancellor@...il.com>
> ---
>  drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> index 7bc2486167e7..affbff76758c 100644
> --- a/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> +++ b/drivers/gpu/drm/amd/amdgpu/gfx_v9_0.c
> @@ -735,7 +735,7 @@ void gfx_v9_0_rlcg_wreg(struct amdgpu_device *adev, u32 offset, u32 v)
>         static void *spare_int;
>         static uint32_t grbm_cntl;
>         static uint32_t grbm_idx;
> -       bool shadow;
> +       bool shadow = false;
>
>         scratch_reg0 = adev->rmmio + (adev->reg_offset[GC_HWIP][0][mmSCRATCH_REG0_BASE_IDX] + mmSCRATCH_REG0)*4;
>         scratch_reg1 = adev->rmmio + (adev->reg_offset[GC_HWIP][0][mmSCRATCH_REG1_BASE_IDX] + mmSCRATCH_REG1)*4;
> --
> 2.26.0.rc1
>
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-- 
Thanks,
~Nick Desaulniers