Segfault in frequency_map when lattice has CHARGE element
Posted: 05 Feb 2020, 20:11
Hi all,
I found an interesting crash - when lattice has CHARGE element, &frequency_map results in segfault.
After (painfully) building elegant with debug symbols, I think the problem stems from the way do_tracking() is called from computeTunesFromTracking() with increasing pass offset, which for all but first call misses charge initialization and crashes at subsequent NULL pointer access. See below for detail.
I have not studied how to properly fix the issue, but in case anyone else gets stuck, the workaround is simple:
-Nikita
Backtrace:
I found an interesting crash - when lattice has CHARGE element, &frequency_map results in segfault.
After (painfully) building elegant with debug symbols, I think the problem stems from the way do_tracking() is called from computeTunesFromTracking() with increasing pass offset, which for all but first call misses charge initialization and crashes at subsequent NULL pointer access. See below for detail.
I have not studied how to properly fix the issue, but in case anyone else gets stuck, the workaround is simple:
Code: Select all
&transmute_elements
name = *, type = CHARGE, new_type = MARK
&endBacktrace:
Code: Select all
...
Starting DRIFT_142#1 at s=3.986823e+01 m, pass 0, 1 particles, memory 15249 kB
Tracking fiducial particle completed.
Program received signal SIGSEGV, Segmentation fault.
0x00000000004d163c in do_tracking (beam=0x0, coord=0xba0bd0, nOriginal=1, effort=0x0, beamline=0xa95080, P_central=0x7ffffffe6450, accepted=0x0, sums_vs_z=0x0, n_z_points=0x0, traj_vs_z=0x0,
run=0x9eb100 <run_conditions>, step=0, flags=65578, n_passes=1, passOffset=1, sasefel=0x0, sliceAnalysis=0x0, finalCharge=0x0, lostParticles=0x0, startElem=0x0) at ../do_tracking.c:1241
warning: Source file is more recent than executable.
1241 if (charge->chargePerParticle)
Missing separate debuginfos, use: debuginfo-install atlas-3.10.1-12.el7.x86_64 blas-3.4.2-8.el7.x86_64 glibc-2.17-260.el7.x86_64 gsl-1.15-13.el7.x86_64 lapack-3.4.2-8.el7.x86_64 libgcc-4.8.5-28.el7.x86_64 libgfortran-4.8.5-28.el7.x86_64 libquadmath-4.8.5-28.el7.x86_64 libstdc++-4.8.5-28.el7.x86_64 zlib-1.2.7-17.el7.x86_64
(gdb) bt
#0 0x00000000004d163c in do_tracking (beam=0x0, coord=0xba0bd0, nOriginal=1, effort=0x0, beamline=0xa95080, P_central=0x7ffffffe6450, accepted=0x0, sums_vs_z=0x0, n_z_points=0x0, traj_vs_z=0x0,
run=0x9eb100 <run_conditions>, step=0, flags=65578, n_passes=1, passOffset=1, sasefel=0x0, sliceAnalysis=0x0, finalCharge=0x0, lostParticles=0x0, startElem=0x0) at ../do_tracking.c:1241
#1 0x00000000005bc486 in computeTunesFromTracking (tune=0x7ffffffe6610, amp=0x7ffffffe6590, M=0x0, beamline=0xa95080, run=0x9eb100 <run_conditions>, startingCoord=0x7ffffffe65d0,
xAmplitude=9.9999999999999995e-07, yAmplitude=9.9999999999999995e-07, deltaOffset=0, turns=256, turnOffset=0, endingCoord=0x7ffffffe65a0, tuneLowerLimit=0x0, tuneUpperLimit=0x0, allowLosses=1,
nPeriods=1, flags=3) at ../twiss.cc:3820
#2 0x0000000000601472 in doFrequencyMap (run=0x9eb100 <run_conditions>, control=0x9eb000 <run_control>, referenceCoord=0xa60f70, errcon=0x7ffffffecc00, beamline=0xa95080) at ../frequencyMap.c:245
#3 0x00000000004e4882 in main (argc=2, argv=0x7fffffffd0b8) at ../elegant.c:1586
(gdb) l
1236 if (nOriginal)
1237 charge->macroParticleCharge = charge->charge/(nOriginal);
1238 }
1239 #endif
1240 }
1241 if (charge->chargePerParticle)
1242 charge->macroParticleCharge = charge->chargePerParticle;
1243 if (charge->macroParticleCharge<0)
1244 bombElegantVA("Error: CHARGE element should specify the quantity of charge (in Coulombs) without the sign. Specified value is %g\n", charge->charge);
1245 break;
(gdb) print charge
$1 = (CHARGE *) 0x0
(gdb) print i_pass
$2 = 1
(gdb)