[mapserver-users] Fwd: segfault using msLayerGetShape

[Steve Lime]

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From: Sylvain Pasche <sylvain_pasche@yahoo.fr>
Message-Id: <15678.37939.408605.394880@in3sun3.epfl.ch>
Date: Wed, 24 Jul 2002 13:49:07 +0200
To: mapserver-bugs@lists.gis.umn.edu
Subject: segfault using msLayerGetShape
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hi, 

I'm using cvs mapserver version of yesterday.

I was trying to do the following in php mapscript:

I run a query with layer->queryByPoint, then get the resulcache: 
for ($res_idx=0; $res_idx < $num_results; $res_idx++) {
                $cache = $layer->getResult($res_idx);

and finally run the function:

   $shape = $layer->getShape($cache->tileindex, 
                                          $cache->shapeindex)

which makes mapserver crash with a SEGMENTATION fault (I'm using
php-4.2.1 cgi) 
I don't know if the problem is tied to php mapscript, ie if a
structure is not initialized correctly. Or I am doing something wrong
in the code sequence before.

here's the backtrace:

(gdb) bt
#0  0x40133bfe in obstack_exit_failure () from /lib/libc.so.6
#1  0x401e6718 in ?? ()
#2  0x40137f5b in errno () from /lib/libc.so.6
#3  0x4235d00f in msSHPReadShape (psSHP=0x83856c8, hEntity=20,
shape=0x82383b8) at mapshape.c:908
#4  0x42394302 in msLayerGetShape (layer=0x42a62b70, shape=0x82383b8,
tile=-1, record=20)
    at maplayer.c:256
#5  0x423502f8 in layerObj_getShape (self=0x42a62b70, shape=0x82383b8, 
tileindex=-1, shapeindex=20)
    at mapscript_i.c:471
#6  0x423464bc in php3_ms_lyr_getShape (ht=2, return_value=0x82383a4,
this_ptr=0x8364d14,
    return_value_used=1) at php_mapscript.c:6108
#7  0x080dd3b0 in ?? ()
#8  0x080dd57a in ?? ()
#9  0x080dd57a in ?? ()

Apparently the problem in is the fseek call in mapshape.c :

(gdb) fr 3
#3  0x4235d00f in msSHPReadShape (psSHP=0x83856c8, hEntity=20,
shape=0x82383b8) at mapshape.c:908
908         fseek( psSHP->fpSHP, psSHP->panRecOffset[hEntity], 0 );

The *FILE used seems to be wrong:

(gdb) p *psSHP->fpSHP
$2 = {_flags = 1075734032, _IO_read_ptr = 0x401e6730
"(g\036@(g\036@0g\036@", 
  _IO_read_end = 0x401e6738 "0g\036@", _IO_read_base = 0x401e6730
"(g\036@(g\036@0g\036@", 
 _IO_write_base = 0x401e6720 "8g\036@0g\036@ g\036@
g\036@(g\036@(g\036@0g\036@", 
  _IO_write_ptr = 0x401e6720 "8g\036@0g\036@ g\036@
g\036@(g\036@(g\036@0g\036@", 
  _IO_write_end = 0x401e6728 " g\036@ g\036@(g\036@(g\036@0g\036@", 
  _IO_buf_base = 0x401e6728 " g\036@ g\036@(g\036@(g\036@0g\036@", 
  _IO_buf_end = 0x401e6730 "(g\036@(g\036@0g\036@", _IO_save_base =
0x0, _IO_backup_base = 0x0, 
  _IO_save_end = 0x0, _markers = 0x401e6740, _chain = 0x401e6740,
_fileno = 1075734344, 
  _blksize = 1075734344, _old_offset = 1075734352, _cur_column =
26448, 
  _vtable_offset = 30 '\036', _shortbuf = "@", _lock = 0x401e6758,
_offset = 4620243930818963288, 
  __pad1 = 0x401e6760, __pad2 = 0x401e6768, _mode = 1075734376, 
  _unused2 =
"pg\036@pg\036@xg\036@xg\036@\020b8\b\020b8\b\210g\036@\210g\036@\220g\036@\220g\036@\230g\036@\230g\036@
g\036@"}

the filepointer seems rather high.

Don't know if this is a compiler/gdb artifact, but it seems like the
file initialisation (*psSHP->fpSHP *FILE pointer) might not be done
properly. Or perhaps is overwritten somewhere..

Just ask me if you need more infos.

Sylvain





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