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 06:20 +0000, Xiang, Haihao wrote:
> 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.
> 

Will apply this patchset if no more comment.

-Haihao

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