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<== Date ==> <== Thread ==>

Subject: EDM X/Y Plot segfaults
From: Eric Norum <wenorum@lbl.gov>
To: EPICS Tech-Talk <tech-talk@aps.anl.gov>, "Sinclair, John William" <sinclairjw@ornl.gov>
Cc: Gregory Portmann <gregportmann@hotmail.com>, Michael Chin <MJChin@lbl.gov>
Date: Wed, 9 May 2018 10:28:41 -0700
Displaying X/Y data in EDM on OS X and Linux often results in a segmentation fault.  Here’s where the fault occurs:

Program received signal SIGSEGV, Segmentation fault.
0x00007ffff1f16f3c in xyGraphClass::genChronoVector (this=0x96c6f0, i=0, 
    rescale=0x7fffffffc2ec) at ../xygraph.cc:6344
6344       dyValue = ( (double *) yPvData[i] )[ii];
(gdb) where
#0  0x00007ffff1f16f3c in xyGraphClass::genChronoVector (this=0x96c6f0, i=0, 
    rescale=0x7fffffffc2ec) at ../xygraph.cc:6344
#1  0x00007ffff1f1c186 in xyGraphClass::executeDeferred (this=0x96c6f0)
    at ../xygraph.cc:9599
#2  0x00007ffff7afe07d in activeWindowClass::processObjects (this=0x927880)
    at ../act_win.cc:22289
#3  0x00007ffff7af5858 in appContextClass::applicationLoop (this=0x636d20)
    at ../app_pkg.cc:6592
#4  0x0000000000405562 in main (argc=<value optimized out>, 
    argv=<value optimized out>) at ../main.cc:2806
(gdb) list
6339       else {
6340         dyValue = (double) ( (unsigned short *) yPvData[i] )[ii];
6341       }
6342       break;
6343     default:
6344       dyValue = ( (double *) yPvData[i] )[ii];
6345       break;
6346     }
6347
6348     if ( y1AxisStyle[yi] == XYGC_K_AXIS_STYLE_LOG10 ) {
(gdb) print yPvData
$3 = {0x0 <repeats 20 times>}
(gdb) print &yPvData
$4 = (void *(*)[20]) 0x96f240
(gdb) print i
$5 = 0
(gdb) print yPvData[0]
$6 = (void *) 0x0
(gdb) 

For some reason yPvData is full of null pointers which results in a segfault when dereferenced by the [ii] subscript.
Any ideas why this happens sometimes?   I can get a good display maybe two or three times in a row and then get the segfault.

— 
Eric Norum

Replies:
Re: EDM X/Y Plot segfaults Eric Norum
Re: EDM X/Y Plot segfaults Eric Norum

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