Re: [FFmpeg-devel] [PATCH 2/8] lavfi/vf_vpp_qsv: handle NULL pointer when evaluating an expression

["Xiang, Haihao" <haihao.xiang-at-intel.com@ffmpeg.org>]

On Do, 2023-01-12 at 05:01 +0100, Andreas Rheinhardt wrote:
> Xiang, Haihao:
> > From: Haihao Xiang <haihao.xiang@intel.com>
> > 
> > This patch provides default value if the expression is NULL.
> > 
> > This is in preparation for reusing the code for other QSV filters.
> > 
> > Signed-off-by: Haihao Xiang <haihao.xiang@intel.com>
> > ---
> >  libavfilter/vf_vpp_qsv.c | 36 ++++++++++++++++++++----------------
> >  1 file changed, 20 insertions(+), 16 deletions(-)
> > 
> > diff --git a/libavfilter/vf_vpp_qsv.c b/libavfilter/vf_vpp_qsv.c
> > index 8d4227f841..3a0a395732 100644
> > --- a/libavfilter/vf_vpp_qsv.c
> > +++ b/libavfilter/vf_vpp_qsv.c
> > @@ -172,14 +172,19 @@ enum var_name {
> >  static int eval_expr(AVFilterContext *ctx)
> >  {
> >  #define PASS_EXPR(e, s) {\
> > -    ret = av_expr_parse(&e, s, var_names, NULL, NULL, NULL, NULL, 0, ctx);
> > \
> > -    if (ret < 0) {\
> > -        av_log(ctx, AV_LOG_ERROR, "Error when passing '%s'.\n", s);\
> > -        goto release;\
> > +    if (s) {\
> > +        ret = av_expr_parse(&e, s, var_names, NULL, NULL, NULL, NULL, 0,
> > ctx); \
> > +        if (ret < 0) {                                                  \
> > +            av_log(ctx, AV_LOG_ERROR, "Error when passing '%s'.\n", s); \
> > +            goto release;                                               \
> > +        }                                                               \
> >      }\
> >  }
> > -#define CALC_EXPR(e, v, i) {\
> > -    i = v = av_expr_eval(e, var_values, NULL); \
> > +#define CALC_EXPR(e, v, i, d) {\
> > +    if (e)\
> > +        i = v = av_expr_eval(e, var_values, NULL);      \
> > +    else\
> > +        i = v = d;\
> >  }
> >      VPPContext *vpp = ctx->priv;
> >      double  var_values[VAR_VARS_NB] = { NAN };
> > @@ -209,30 +214,29 @@ static int eval_expr(AVFilterContext *ctx)
> >      var_values[VAR_DAR] = var_values[VAR_A] * var_values[VAR_SAR];
> >  
> >      /* crop params */
> > -    CALC_EXPR(cw_expr, var_values[VAR_CW], vpp->crop_w);
> > -    CALC_EXPR(ch_expr, var_values[VAR_CH], vpp->crop_h);
> > +    CALC_EXPR(cw_expr, var_values[VAR_CW], vpp->crop_w,
> > var_values[VAR_IW]);
> > +    CALC_EXPR(ch_expr, var_values[VAR_CH], vpp->crop_h,
> > var_values[VAR_IH]);
> >  
> >      /* calc again in case cw is relative to ch */
> > -    CALC_EXPR(cw_expr, var_values[VAR_CW], vpp->crop_w);
> > +    CALC_EXPR(cw_expr, var_values[VAR_CW], vpp->crop_w,
> > var_values[VAR_IW]);
> >  
> >      CALC_EXPR(w_expr,
> >              var_values[VAR_OUT_W] = var_values[VAR_OW] = var_values[VAR_W],
> > -            vpp->out_width);
> > +            vpp->out_width, var_values[VAR_CW]);
> >      CALC_EXPR(h_expr,
> >              var_values[VAR_OUT_H] = var_values[VAR_OH] = var_values[VAR_H],
> > -            vpp->out_height);
> > +            vpp->out_height, var_values[VAR_CH]);
> >  
> >      /* calc again in case ow is relative to oh */
> >      CALC_EXPR(w_expr,
> >              var_values[VAR_OUT_W] = var_values[VAR_OW] = var_values[VAR_W],
> > -            vpp->out_width);
> > +            vpp->out_width, var_values[VAR_CW]);
> >  
> > -
> > -    CALC_EXPR(cx_expr, var_values[VAR_CX], vpp->crop_x);
> > -    CALC_EXPR(cy_expr, var_values[VAR_CY], vpp->crop_y);
> > +    CALC_EXPR(cx_expr, var_values[VAR_CX], vpp->crop_x, (var_values[VAR_IW]
> > - var_values[VAR_OW]) / 2);
> > +    CALC_EXPR(cy_expr, var_values[VAR_CY], vpp->crop_y, (var_values[VAR_IH]
> > - var_values[VAR_OH]) / 2);
> >  
> >      /* calc again in case cx is relative to cy */
> > -    CALC_EXPR(cx_expr, var_values[VAR_CX], vpp->crop_x);
> > +    CALC_EXPR(cx_expr, var_values[VAR_CX], vpp->crop_x, (var_values[VAR_IW]
> > - var_values[VAR_OW]) / 2);
> >  
> >      if ((vpp->crop_w != var_values[VAR_IW]) || (vpp->crop_h !=
> > var_values[VAR_IH]))
> >          vpp->use_crop = 1;
> 
> Does this add runtime checks to cases where there are not necessary?

No. It is irrelated to runtime check. It is used to make sure each variable have
a right default value even if the corresponding expression is NULL.

E.g. vpp->cw is NULL when we re-use functions and data structures in
vf_vpp_qsv.c and qsvvpp.c for deinterlace_qsv filter.

Thanks
Haihao


> 
> - Andreas
> 
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