[postgis-tickets] [PostGIS] #3281: Avoid exporting symbols in the postgresql module

[PostGIS]

#3281: Avoid exporting symbols in the postgresql module
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  Reporter:  strk                   |      Owner:  strk
      Type:  enhancement            |     Status:  closed
  Priority:  medium                 |  Milestone:  PostGIS 2.2.0
 Component:  build/upgrade/install  |    Version:  trunk
Resolution:  fixed                  |   Keywords:
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Comment (by strk):

 For the record, I went deep to find the actual problem and here's the
 result:
 {{{
 [lwin_wkb.c:lwpoint_from_wkb_state:418] calling lwpoint_construct
 lwpoint_construct from PostGIS 1.5 here
 }}}

 Basically a "lwpoint_from_wkb_state" function from liblwgeom-2.2.0
 (dynamically linked) ends up calling "lwpoint_construct" not from itself,
 but from the liblwgeom version statically linked in the PostGIS-1.5 module
 loaded by the same PostgreSQL backend process loading the module which
 dynalinks to liblwgeom-2.2.0.

 This is probably due to the fact that the "lwpoint_construct" symbol was
 resolved before the dynalinking module was even loaded, so it was found in
 the process at the time of lookup.

 In turn, this explains why _omitting_ to export the statically-linked
 symbols from PostGIS-1.5 fixes the issue.

 Statically linking liblwgeom in the new module also fixes the issue
 because there's no runtime linking involved in calling all those functions
 (I think).

 These findings may be of interest for @darkblue_b

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Ticket URL: <https://trac.osgeo.org/postgis/ticket/3281#comment:6>
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