[PATCH] drm/amdgpu: Senseless code and unnecessary memset

[PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Grigory Vasilyev]

Using memset on local arrays before exiting the function is pointless.
Compilator will remove this code. Also for local arrays is preferable to
use {0} instead of memset. Mistakes are often made when working with
memset.

Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
---
 drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
index be9d61bcb8ae..537e48fbbe6b 100644
--- a/drivers/gpu/drm/amd/amdgpu/atom.c
+++ b/drivers/gpu/drm/amd/amdgpu/atom.c
@@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
 int amdgpu_atom_asic_init(struct atom_context *ctx)
 {
 	int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
-	uint32_t ps[16];
+	uint32_t ps[16] = {0};
 	int ret;
 
-	memset(ps, 0, 64);
-
 	ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
 	ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
 	if (!ps[0] || !ps[1])
@@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
 	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
 		return 1;
 	ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
-	if (ret)
-		return ret;
-
-	memset(ps, 0, 64);
 
 	return ret;
 }
-- 
2.35.1

Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Christian König]

Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
> Using memset on local arrays before exiting the function is pointless.
> Compilator will remove this code. Also for local arrays is preferable to
> use {0} instead of memset. Mistakes are often made when working with
> memset.

Well actually memset is preferred when working with structures which are 
given to the hardware parser because {0} won't initialize paddings.

So please don't use {0} in any of the atom bios code.

Regards,
Christian.

>
> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
>   1 file changed, 1 insertion(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
> index be9d61bcb8ae..537e48fbbe6b 100644
> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
>   int amdgpu_atom_asic_init(struct atom_context *ctx)
>   {
>   	int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
> -	uint32_t ps[16];
> +	uint32_t ps[16] = {0};
>   	int ret;
>   
> -	memset(ps, 0, 64);
> -
>   	ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
>   	ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
>   	if (!ps[0] || !ps[1])
> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
>   	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
>   		return 1;
>   	ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
> -	if (ret)
> -		return ret;
> -
> -	memset(ps, 0, 64);
>   
>   	return ret;
>   }

Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Jani Nikula]

On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote:
> Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
>> Using memset on local arrays before exiting the function is pointless.
>> Compilator will remove this code. Also for local arrays is preferable to
>> use {0} instead of memset. Mistakes are often made when working with
>> memset.
>
> Well actually memset is preferred when working with structures which are 
> given to the hardware parser because {0} won't initialize paddings.

Not that I'd know anything that's going on here... but it sure seems
strange to me to be passing unpacked structures where the padding might
matter to a "hardware parser".

*shrug*


BR,
Jani.


>
> So please don't use {0} in any of the atom bios code.
>
> Regards,
> Christian.
>
>>
>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
>> ---
>>   drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
>>   1 file changed, 1 insertion(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
>> index be9d61bcb8ae..537e48fbbe6b 100644
>> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
>> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
>> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
>>   int amdgpu_atom_asic_init(struct atom_context *ctx)
>>   {
>>   	int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
>> -	uint32_t ps[16];
>> +	uint32_t ps[16] = {0};
>>   	int ret;
>>   
>> -	memset(ps, 0, 64);
>> -
>>   	ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
>>   	ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
>>   	if (!ps[0] || !ps[1])
>> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
>>   	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
>>   		return 1;
>>   	ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
>> -	if (ret)
>> -		return ret;
>> -
>> -	memset(ps, 0, 64);
>>   
>>   	return ret;
>>   }
>

-- 
Jani Nikula, Intel Open Source Graphics Center

Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Christian König]

Am 06.04.22 um 16:26 schrieb Jani Nikula:
> On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote:
>> Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
>>> Using memset on local arrays before exiting the function is pointless.
>>> Compilator will remove this code. Also for local arrays is preferable to
>>> use {0} instead of memset. Mistakes are often made when working with
>>> memset.
>> Well actually memset is preferred when working with structures which are
>> given to the hardware parser because {0} won't initialize paddings.
> Not that I'd know anything that's going on here... but it sure seems
> strange to me to be passing unpacked structures where the padding might
> matter to a "hardware parser".

Well to me it is an absolute miracle why the heck compilers don't 
initialize paddings.

We had so many ups moments over the years and I really don't see why it 
should be more optimal to do this.

Anyway, the memset() is used intentionally here and I don't really want 
to change it. What we could do is removing the second superfluous memset 
and use sizeof() instead of hard coding the size.

Regards,
Christian.

>
> *shrug*
>
>
> BR,
> Jani.
>
>
>> So please don't use {0} in any of the atom bios code.
>>
>> Regards,
>> Christian.
>>
>>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
>>> ---
>>>    drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
>>>    1 file changed, 1 insertion(+), 7 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
>>> index be9d61bcb8ae..537e48fbbe6b 100644
>>> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
>>> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
>>> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
>>>    int amdgpu_atom_asic_init(struct atom_context *ctx)
>>>    {
>>>    	int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
>>> -	uint32_t ps[16];
>>> +	uint32_t ps[16] = {0};
>>>    	int ret;
>>>    
>>> -	memset(ps, 0, 64);
>>> -
>>>    	ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
>>>    	ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
>>>    	if (!ps[0] || !ps[1])
>>> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
>>>    	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
>>>    		return 1;
>>>    	ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
>>> -	if (ret)
>>> -		return ret;
>>> -
>>> -	memset(ps, 0, 64);
>>>    
>>>    	return ret;
>>>    }

Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Grigory Vasilyev]

Christian König in fact the compiler will very often replace {0} with
a memset call. I don't see a problem using {0} for local arrays with
primitive types.
There should also be no problem with memory alignment. Because the
compiler understands it. Using sizeof is also not a good idea.
More often everyone also makes mistakes with sizeof. It's best to
leave it as is, and there's no errors.
Indeed, when using structures and {0}, errors may occur, but I am not
aware of errors when using primitive types. I also looked at the
amdgpu code and  {0} is used in many places.
Also from experience malloc+memset is the most dangerous chain, can
silently damage memory, causing a bunch of subtle problems, and it is
better to replace them with more safe calloc.
Such a problem, for example, was recently found by me in fontconfig
and it crashed intel quartus. Therefore, where possible, I try to
avoid memset.

Regards, Grigory.

ср, 6 апр. 2022 г. в 17:43, Christian König <christian.koenig@amd.com>:
>
> Am 06.04.22 um 16:26 schrieb Jani Nikula:
> > On Tue, 05 Apr 2022, Christian König <christian.koenig@amd.com> wrote:
> >> Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
> >>> Using memset on local arrays before exiting the function is pointless.
> >>> Compilator will remove this code. Also for local arrays is preferable to
> >>> use {0} instead of memset. Mistakes are often made when working with
> >>> memset.
> >> Well actually memset is preferred when working with structures which are
> >> given to the hardware parser because {0} won't initialize paddings.
> > Not that I'd know anything that's going on here... but it sure seems
> > strange to me to be passing unpacked structures where the padding might
> > matter to a "hardware parser".
>
> Well to me it is an absolute miracle why the heck compilers don't
> initialize paddings.
>
> We had so many ups moments over the years and I really don't see why it
> should be more optimal to do this.
>
> Anyway, the memset() is used intentionally here and I don't really want
> to change it. What we could do is removing the second superfluous memset
> and use sizeof() instead of hard coding the size.
>
> Regards,
> Christian.
>
> >
> > *shrug*
> >
> >
> > BR,
> > Jani.
> >
> >
> >> So please don't use {0} in any of the atom bios code.
> >>
> >> Regards,
> >> Christian.
> >>
> >>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.com>
> >>> ---
> >>>    drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
> >>>    1 file changed, 1 insertion(+), 7 deletions(-)
> >>>
> >>> diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> index be9d61bcb8ae..537e48fbbe6b 100644
> >>> --- a/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
> >>> @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
> >>>    int amdgpu_atom_asic_init(struct atom_context *ctx)
> >>>    {
> >>>     int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
> >>> -   uint32_t ps[16];
> >>> +   uint32_t ps[16] = {0};
> >>>     int ret;
> >>>
> >>> -   memset(ps, 0, 64);
> >>> -
> >>>     ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
> >>>     ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
> >>>     if (!ps[0] || !ps[1])
> >>> @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
> >>>     if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
> >>>             return 1;
> >>>     ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
> >>> -   if (ret)
> >>> -           return ret;
> >>> -
> >>> -   memset(ps, 0, 64);
> >>>
> >>>     return ret;
> >>>    }
>