Re: [PATCH] [media] vivid: don't use more than 1024 bytes of stack

[Hans Verkuil <hverkuil@xs4all.nl>]

On 06/05/2015 12:29 PM, Mauro Carvalho Chehab wrote:
> Remove the following compilation warnings:
> 
> 	drivers/media/platform/vivid/vivid-tpg.c: In function 'tpg_gen_text':
> 	drivers/media/platform/vivid/vivid-tpg.c:1562:1: warning: the frame size of 1308 bytes is larger than 1024 bytes [-Wframe-larger-than=]
> 	 }
> 	 ^
> 
> This seems to be due to some bad optimization done by gcc.
> 
> Moving the for() loop to happen inside the macro solves the
> issue.
> 
> While here, fix CodingStyle at the switch().
> 
> Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>
> 
> diff --git a/drivers/media/platform/vivid/vivid-tpg.c b/drivers/media/platform/vivid/vivid-tpg.c
> index b1147f2df26c..7a3ed580626a 100644
> --- a/drivers/media/platform/vivid/vivid-tpg.c
> +++ b/drivers/media/platform/vivid/vivid-tpg.c
> @@ -1492,12 +1492,10 @@ void tpg_gen_text(const struct tpg_data *tpg, u8 *basep[TPG_MAX_PLANES][2],
>  	else if (tpg->field == V4L2_FIELD_SEQ_TB || tpg->field == V4L2_FIELD_SEQ_BT)
>  		div = 2;
>  
> -	for (p = 0; p < tpg->planes; p++) {
> -		unsigned vdiv = tpg->vdownsampling[p];
> -		unsigned hdiv = tpg->hdownsampling[p];
> -
> -		/* Print text */
> -#define PRINTSTR(PIXTYPE) do {	\
> +	/* Print text */
> +#define PRINTSTR(PIXTYPE) for (p = 0; p < tpg->planes; p++) {	\
> +	unsigned vdiv = tpg->vdownsampling[p];	\
> +	unsigned hdiv = tpg->hdownsampling[p];	\
>  	PIXTYPE fg;	\
>  	PIXTYPE bg;	\
>  	memcpy(&fg, tpg->textfg[p], sizeof(PIXTYPE));	\
> @@ -1548,16 +1546,19 @@ void tpg_gen_text(const struct tpg_data *tpg, u8 *basep[TPG_MAX_PLANES][2],
>  	}	\
>  } while (0)
>  
> -		switch (tpg->twopixelsize[p]) {
> -		case 2:
> -			PRINTSTR(u8); break;
> -		case 4:
> -			PRINTSTR(u16); break;
> -		case 6:
> -			PRINTSTR(x24); break;
> -		case 8:
> -			PRINTSTR(u32); break;
> -		}
> +	switch (tpg->twopixelsize[p]) {

This doesn't work I just discovered. Compiling gives this warning:

drivers/media/platform/vivid/vivid-tpg.c: In function ‘tpg_gen_text’:
drivers/media/platform/vivid/vivid-tpg.c:1549:27: warning: ‘p’ may be used uninitialized in this function [-Wmaybe-uninitialized]
  switch (tpg->twopixelsize[p]) {
                           ^

And the value for tpg->twopixelsize[p] will actually differ depending on the value of p.

It's probably best to revert this patch.

The correct approach is likely to make four functions, one for case,
with the macro as the function body.

Regards,

	Hans

> +	case 2:
> +		PRINTSTR(u8);
> +		break;
> +	case 4:
> +		PRINTSTR(u16);
> +		break;
> +	case 6:
> +		PRINTSTR(x24);
> +		break;
> +	case 8:
> +		PRINTSTR(u32);
> +		break;
>  	}
>  }
>  
>