Re: segfault in plot3d

[Ethan A M. <merritt@u.washington.edu>]

On Tuesday 17 February 2009, James R. Van Zandt wrote:
> 
> I ran across a reliable segfault with the splot command, with the
> current CVS code:
> 
>         G N U P L O T
>         Version 4.3 patchlevel 0
>         last modified February 2009

I can reproduce the bug.
I bisected it back to a single patch to plot3d on 20-Oct-2006.
The patch added support for iteration.  

http://gnuplot.cvs.sourceforge.net/viewvc/gnuplot/gnuplot/src/plot3d.c?r1=1.132&r2=1.133&view=patch

And there I lose it.  I can't see what that check for iteration has to do with this crash.
There is no iteration in the command that triggers the crash, so the iteration
code should not do anything at all.  Yet reverting that one set of checks makes the
crash go away.

Can anyone else see what is going on?

	Ethan


 
> In particular, this is *without* my proposed changes to fit.c
> 
> Here's a run under the debugger:
> 
> gnuplot> splot 'lin2.dat',x+y
> [New Thread 0xb7843a40 (LWP 27810)]
> 
> Program received signal SIGSEGV, Segmentation fault.
> [Switching to Thread 0xb7843a40 (LWP 27810)]
> calculate_set_of_isolines (value_axis=FIRST_Z_AXIS, cross=false, this_iso=0xbffb32e0, iso_axis=FIRST_Y_AXIS, iso_min=2, iso_step=0.33333333333333331, num_iso_to_use=10, sam_axis=FIRST_X_AXIS, sam_min=1, sam_step=0.030303030303030304, num_sam_to_use=100, need_palette=false) at plot3d.c:1174
> (gdb) backtrace
> #0  calculate_set_of_isolines (value_axis=FIRST_Z_AXIS, cross=false, this_iso=0xbffb32e0, iso_axis=FIRST_Y_AXIS, iso_min=2, iso_step=0.33333333333333331, num_iso_to_use=10, sam_axis=FIRST_X_AXIS, sam_min=1, sam_step=0.030303030303030304, num_sam_to_use=100, need_palette=false) at plot3d.c:1174
> #1  0x080a808c in plot3drequest () at plot3d.c:1909
> #2  0x080571d7 in do_line () at command.c:595
> #3  0x0805796d in com_line () at command.c:338
> #4  0x0809a6dd in main (argc=1, argv=0xbffb35a4) at plot.c:659
> (gdb) 
> 
> Here's lin2.dat:
> ---------------------------------------------
> #octave:9> for x=[1:4];for y=[2:5]; fprintf('%f %f %f 1\n',x,y,10*x+2*y+randn);end;end
> 1.000000 2.000000 13.753875 1
> 1.000000 3.000000 15.843192 1
> 1.000000 4.000000 17.752269 1
> 1.000000 5.000000 18.819627 1
> 
> 
> 2.000000 2.000000 25.480149 1
> 2.000000 3.000000 26.217588 1
> 2.000000 4.000000 28.555638 1
> 2.000000 5.000000 30.757950 1
> 
> 
> 3.000000 2.000000 33.879955 1
> 3.000000 3.000000 36.190724 1
> 3.000000 4.000000 39.199289 1
> 3.000000 5.000000 40.153219 1
> 
> 
> 4.000000 2.000000 43.413695 1
> 4.000000 3.000000 45.938903 1
> 4.000000 4.000000 49.196757 1
> 4.000000 5.000000 50.136290 1
> #octave:10> diary off
> -----------------------------------------
> 
> 
> All these commands work fine:
> 
>    gnuplot> splot 'fit2.dat'
>    gnuplot> splot x+y
>    gnuplot> splot x+y,'fit2.dat'
> 
> It only fails when plotting the data file first, then the function.
> I've had other data files fail, but demo/glasses.dat succeeds.
> 
> I set a breakpoint at plot3d.c:1174 in calculate_set_of_isolines() and
> followed execution.  When j=0 and i=99, the function reaches end of
> the linked list, sets this_iso to zero, then sets points to zero.  The
> next time through when j=1 and i=0, the function dies trying to access
> points[i].x.  I haven't been able to identify the cause.
> 
> I have a couple of other binaries installed.
> This version also crashes:
>         G N U P L O T
>         Version 4.3 patchlevel 0
>         last modified January 2007
> 
> This version is okay:
>         G N U P L O T
>         Version 4.2 patchlevel 4 
>         last modified Sep 2008
> 
> 
> Does anyone else see this?
> 
>      - Jim Van Zandt
> 
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-- 
Ethan A Merritt
Biomolecular Structure Center
University of Washington, Seattle 98195-7742