error in examples for davinci media controller

Jan Pohanka

Hello,

there is an error in provided media controller examples

struct media_entity_desc entity[10];
...
/* 4.enumerate media-entities */
printf("4.enumerating media entities\n");
index = 0;
do {
memset(&entity[index], 0, sizeof(entity));
...
index++;
} while ...

This code can rewrite uninitialized memory. The solution is to do the memset before the cycle on whole entity array. It affects all files in mc subdirectory and it is also on the wiki.
Anyway, the quality of all code in examples is really poor, IMHO.

best regards
Jan

over 13 years ago

0 Prabhakar Lad over 13 years ago

Guru 11260 points

The intent is to zero out the memory. What do you mean by rewrite uninitialized memory?

Agreed, this could have been done in on shot for the whole array.

Thx,

Prabhakar Lad

0 Mike Whittaker over 13 years ago in reply to Prabhakar Lad

Intellectual 410 points

I think the problem is with

memset(&entity[index], 0, sizeof(entity));

since sizeof(entity) is the size of the whole array - it will overwrite memory outside entity[] once index > 0.

If they insist on using a loop, it should just be

memset(&entity[index], 0, sizeof(struct media_entity_desc));

0 Prabhakar Lad over 13 years ago in reply to Mike Whittaker

Guru 11260 points

Hi Mike,

Yes.. thats right it needs to be fixed didnt notice it..

@Jan : Can you also post the which wiki link were you referring to so that I can as the TI folks to fix it.

Thx,

--Prabhakar Lad

0 Jan Pohanka over 13 years ago in reply to Prabhakar Lad

Expert 1310 points

Hi,

here is the wiki link
http://processors.wiki.ti.com/index.php/Writing_V4L2_Media_Controller_Applications_on_Dm36x_Video_Capture

Regarding the Mike's advice with memset(&entity[index], 0, sizeof(struct media_entity_desc)); within the loop: be careful with that, because you are using do .. while() loop and the memset is called ARRAY_LENGTH(entity) + 1 times so it will be again overwriting memory outside the entity[]. Valgrind is a good tool to find errors like that, but unfortunately it cannot be compiled for dm365 (armv5)

As I said in my first post I think that code in the examples should be reviewed, it is not very clear...

regards
Jan

0 Prabhakar Lad over 13 years ago in reply to Jan Pohanka

Guru 11260 points

Hi,

Thanks, I'll definitely forward this wiki link to be corrected, and also make sure the application's code is cleaned up.

Thx,

--Prabhakar Lad

0 Mike Whittaker over 13 years ago in reply to Jan Pohanka

Intellectual 410 points

"the memset is called ARRAY_LENGTH(entity) + 1"

That was not evident from the original post since the loop termination condition is not shown.

In any case, the dimension of the array, 10, should be given as a #define so that the same symbolic constant can be used elsewhere, eg. "while (index < NUMBER_OF_ENTITIES) "

0 Prabhakar Lad over 13 years ago in reply to Mike Whittaker

Guru 11260 points

Hi,

The wiki link http://processors.wiki.ti.com/index.php/Writing_V4L2_Media_Controller_Applications_on_Dm36x_Video_Capture

has been updated.

Thx,

--Prabhakar Lad

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error in examples for davinci media controller