linux-kernel - Re: [PATCH] drivers: gpu: Fix warning using plain integer as NULL

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Message-ID: <ba31f441-80cd-4745-b425-23e5b9e0f9c0@gmail.com>
Date:   Mon, 6 Nov 2023 23:49:14 +0530
From:   Abhinav Singh <singhabhinav9051571833@...il.com>
To:     Jani Nikula <jani.nikula@...ux.intel.com>,
        alexander.deucher@....com, christian.koenig@....com,
        Xinhui.Pan@....com, airlied@...il.com, daniel@...ll.ch
Cc:     linux-kernel-mentees@...ts.linuxfoundation.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers: gpu: Fix warning using plain integer as NULL

On 11/6/23 22:10, Jani Nikula wrote:
> On Mon, 06 Nov 2023, Abhinav Singh <singhabhinav9051571833@...il.com> wrote:
>> On 11/6/23 16:53, Jani Nikula wrote:
>>> On Fri, 03 Nov 2023, Abhinav Singh <singhabhinav9051571833@...il.com> wrote:
>>>> sparse static analysis tools generate a warning with this message
>>>> "Using plain integer as NULL pointer". In this case this warning is
>>>> being shown because we are trying to intialize a pointer to NULL using
>>>> integer value 0.
>>>>
>>>> Signed-off-by: Abhinav Singh <singhabhinav9051571833@...il.com>
>>>> ---
>>>>    drivers/gpu/drm/radeon/clearstate_evergreen.h | 8 ++++----
>>>>    1 file changed, 4 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/gpu/drm/radeon/clearstate_evergreen.h b/drivers/gpu/drm/radeon/clearstate_evergreen.h
>>>> index 63a1ffbb3ced..3b645558f133 100644
>>>> --- a/drivers/gpu/drm/radeon/clearstate_evergreen.h
>>>> +++ b/drivers/gpu/drm/radeon/clearstate_evergreen.h
>>>> @@ -1049,7 +1049,7 @@ static const struct cs_extent_def SECT_CONTEXT_defs[] =
>>>>        {SECT_CONTEXT_def_5, 0x0000a29e, 5 },
>>>>        {SECT_CONTEXT_def_6, 0x0000a2a5, 56 },
>>>>        {SECT_CONTEXT_def_7, 0x0000a2de, 290 },
>>>> -    { 0, 0, 0 }
>>>> +    { NULL, 0, 0 }
>>>
>>> Random drive-by comment:
>>>
>>> I'd just use {} as the sentinel.
>>>
>>> BR,
>>> Jani.
>>>
>>>>    };
>>>>    static const u32 SECT_CLEAR_def_1[] =
>>>>    {
>>>> @@ -1060,7 +1060,7 @@ static const u32 SECT_CLEAR_def_1[] =
>>>>    static const struct cs_extent_def SECT_CLEAR_defs[] =
>>>>    {
>>>>        {SECT_CLEAR_def_1, 0x0000ffc0, 3 },
>>>> -    { 0, 0, 0 }
>>>> +    { NULL, 0, 0 }
>>>>    };
>>>>    static const u32 SECT_CTRLCONST_def_1[] =
>>>>    {
>>>> @@ -1070,11 +1070,11 @@ static const u32 SECT_CTRLCONST_def_1[] =
>>>>    static const struct cs_extent_def SECT_CTRLCONST_defs[] =
>>>>    {
>>>>        {SECT_CTRLCONST_def_1, 0x0000f3fc, 2 },
>>>> -    { 0, 0, 0 }
>>>> +    { NULL, 0, 0 }
>>>>    };
>>>>    static const struct cs_section_def evergreen_cs_data[] = {
>>>>        { SECT_CONTEXT_defs, SECT_CONTEXT },
>>>>        { SECT_CLEAR_defs, SECT_CLEAR },
>>>>        { SECT_CTRLCONST_defs, SECT_CTRLCONST },
>>>> -    { 0, SECT_NONE }
>>>> +    { NULL, SECT_NONE }
>>>>    };
>>>> --
>>>> 2.39.2
>>>>
>>>
>> Hi, Thanks for dropping by and the suggestion. I thought of using NULL
>> instead of {} is because, first the warning itself says that 0 is used
>> to intialize pointers with NULL, and second due this link
>> https://www.spinics.net/lists/linux-sparse/msg10066.html where linus is
>> talking about not using 0 NULL intialization of pointer variable and he
>> thinks this is a legitimate issue and not some false positive
> 
> But... {} is neither of those things. It's empty initialization instead
> of 0. It's valid in GCC and C23, and used all over the place in the
> kernel.
> 
> BR,
> Jani.
> 
> 
> 
If I understand correctly you want to me change from this "{ NULL, 
SECT_NONE }" to "{}" right? If yes, then according to what I read from 
some online, it is better to intialize variables especially pointer 
because in some cases a non initialized pointer doesnt always point to 
NULL. Not sure if this applies in kernel space as well. But yeah my 
knowledge is pretty limited in C in user space and in kernel space it is 
even more limited :)