Experimental Physics and
Industrial Control System

 found that hacking in the following changes seems to stop the segfaults and result in waveform display.  i suspect that there’s a better fix that involves not invoking this method when the pointers in question are invalid, but I don’t have any idea what that would entail.

diff -u baselib/xygraph.cc.orig baselib/xygraph.cc

--- baselib/xygraph.cc.orig 2018-05-09 10:49:02.055680000 -0700

+++ baselib/xygraph.cc 2018-05-09 10:52:04.804485000 -0700

@@ -6298,6 +6298,7 @@

   arrayNumPoints[i] = 0;

 

   for ( ii=0; ii<yPvCount[i]; ii++ ) {

+    if (!yPvData[i]) dyValue = 0; else

 

     // There are two views of pv types, Type and specificType; this uses

     // specificType

@@ -6413,7 +6414,7 @@

 

 #endif

 

-    dxValue = ( (double *) xPvData[i] )[ii];

+    if (xPvData[i]) dxValue = ( (double *) xPvData[i] )[ii]; else dxValue = 0;

 

     if ( xAxisStyle == XYGC_K_AXIS_STYLE_LOG10 ) {

       dxValue = loc_log10(  dxValue  );

On May 9, 2018, at 10:28 AM, Eric Norum <[email protected]> wrote:

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.