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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Tue, 23 Mar 2021 11:33:47 -0400
Message-ID: <CADnq5_MYZF2VWe=fYOqj-M5QA2myYTy-Lwu6uchuXZEz+oZbQw@mail.gmail.com>
Subject: Re: [PATCH] amdgpu: fix gcc -Wrestrict warning
To:     Arnd Bergmann <arnd@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>,
        Jinzhou Su <Jinzhou.Su@amd.com>, Arnd Bergmann <arnd@arndb.de>,
        LKML <linux-kernel@vger.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>, Huang Rui <ray.huang@amd.com>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>
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Precedence: bulk

Applied.  Thanks!

Alex

On Tue, Mar 23, 2021 at 9:04 AM Arnd Bergmann <arnd@kernel.org> wrote:
>
> From: Arnd Bergmann <arnd@arndb.de>
>
> gcc warns about an sprintf() that uses the same buffer as source
> and destination, which is undefined behavior in C99:
>
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c: In function 'amdgpu_securedisplay_debugfs_write':
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:141:6: error: 'sprintf' argument 3 overlaps destination object 'i2c_output' [-Werror=restrict]
>   141 |      sprintf(i2c_output, "%s 0x%X", i2c_output,
>       |      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>   142 |       securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
>       |       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c:97:7: note: destination object referenced by 'restrict'-qualified argument 1 was declared here
>    97 |  char i2c_output[256];
>       |       ^~~~~~~~~~
>
> Rewrite it to remember the current offset into the buffer instead.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> index 834440ab9ff7..69d7f6bff5d4 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_securedisplay.c
> @@ -136,9 +136,10 @@ static ssize_t amdgpu_securedisplay_debugfs_write(struct file *f, const char __u
>                 ret = psp_securedisplay_invoke(psp, TA_SECUREDISPLAY_COMMAND__SEND_ROI_CRC);
>                 if (!ret) {
>                         if (securedisplay_cmd->status == TA_SECUREDISPLAY_STATUS__SUCCESS) {
> +                               int pos = 0;
>                                 memset(i2c_output,  0, sizeof(i2c_output));
>                                 for (i = 0; i < TA_SECUREDISPLAY_I2C_BUFFER_SIZE; i++)
> -                                       sprintf(i2c_output, "%s 0x%X", i2c_output,
> +                                       pos += sprintf(i2c_output + pos, " 0x%X",
>                                                 securedisplay_cmd->securedisplay_out_message.send_roi_crc.i2c_buf[i]);
>                                 dev_info(adev->dev, "SECUREDISPLAY: I2C buffer out put is :%s\n", i2c_output);
>                         } else {
> --
> 2.29.2
>
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