[postgis-tickets] [PostGIS] #5558: Compilation warning: uninitialized variable

[PostGIS]

#5558: Compilation warning: uninitialized variable
---------------------------+---------------------------
  Reporter:  Laurenz Albe  |      Owner:  pramsey
      Type:  defect        |     Status:  new
  Priority:  medium        |  Milestone:  PostGIS 3.4.1
 Component:  postgis       |    Version:  master
Resolution:                |   Keywords:
---------------------------+---------------------------
Description changed by Laurenz Albe:

Old description:

> Building master, I get
>
> {{{
> In file included from mvt.h:40,
>                  from mvt.c:30:
> mvt.c: In function ‘mvt_clip_and_validate_geos’:
> mvt.c:884:41: warning: ‘bgbox.flags’ may be used uninitialized [-Wmaybe-
> uninitialized]
>   884 |                 FLAGS_SET_GEODETIC(bgbox.flags, 0);
> ../liblwgeom/liblwgeom.h:175:95: note: in definition of macro
> ‘FLAGS_SET_GEODETIC’
>   175 | #define FLAGS_SET_GEODETIC(flags, value) ((flags) = (value) ?
> ((flags) | LWFLAG_GEODETIC) : ((flags) & ~LWFLAG_GEODETIC))
>       |
> ^~~~~
> mvt.c:881:22: note: ‘bgbox’ declared here
>   881 |                 GBOX bgbox;
>       |                      ^~~~~
> }}}
>
> Indeed, in `postgis/mvt.c`, `bgbox.flag` is not initialized:
>
> {{{#!c
> GBOX bgbox;
> bgbox.xmax = bgbox.ymax = (double)extent + (double)buffer;
> bgbox.xmin = bgbox.ymin = -(double)buffer;
> FLAGS_SET_GEODETIC(bgbox.flags, 0);
> }}}
>
> I guess it should be initialized to zero, as in the following patch:
>
> {{{#!diff
> diff --git a/postgis/mvt.c b/postgis/mvt.c
> index 8aa916052..64bb28edb 100644
> --- a/postgis/mvt.c
> +++ b/postgis/mvt.c
> @@ -881,6 +881,7 @@ mvt_clip_and_validate_geos(LWGEOM *lwgeom, uint8_t
> basic_type, uint32_t extent,
>         GBOX bgbox;
>         bgbox.xmax = bgbox.ymax = (double)extent + (double)buffer;
>         bgbox.xmin = bgbox.ymin = -(double)buffer;
> +       bgbox.flags = 0;
>         FLAGS_SET_GEODETIC(bgbox.flags, 0);
>
>         ng = mvt_unsafe_clip_by_box(ng, &bgbox);
> }}}

New description:

 Building master, I get

 {{{
 In file included from mvt.h:40,
                  from mvt.c:30:
 mvt.c: In function ‘mvt_clip_and_validate_geos’:
 mvt.c:884:41: warning: ‘bgbox.flags’ may be used uninitialized [-Wmaybe-
 uninitialized]
   884 |                 FLAGS_SET_GEODETIC(bgbox.flags, 0);
 ../liblwgeom/liblwgeom.h:175:95: note: in definition of macro
 ‘FLAGS_SET_GEODETIC’
   175 | #define FLAGS_SET_GEODETIC(flags, value) ((flags) = (value) ?
 ((flags) | LWFLAG_GEODETIC) : ((flags) & ~LWFLAG_GEODETIC))
       |
 ^~~~~
 mvt.c:881:22: note: ‘bgbox’ declared here
   881 |                 GBOX bgbox;
       |                      ^~~~~
 }}}

 Indeed, in `postgis/mvt.c`, `bgbox.flag` is not initialized:

 {{{#!c
 GBOX bgbox;
 bgbox.xmax = bgbox.ymax = (double)extent + (double)buffer;
 bgbox.xmin = bgbox.ymin = -(double)buffer;
 FLAGS_SET_GEODETIC(bgbox.flags, 0);
 }}}

 I cannot suggest a patch, because I don't know to what value the `flags`
 should be initialized.

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/5558#comment:1>
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