Infinity cast to integer when creating hair particle system with children #83282
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Reference: blender/blender#83282
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System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080 Ti/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 457.30
Blender Version
Broken:
13c820d87b
Worked: -
Short description of error
Blender tries to cast a float infinity to an integer, when a hair particle system with children is created and displayed in viewport or rendered. This causes undefined behavior.
In
psys_tasks_create
(particle_system.c ) the variablenumtasks
is calculated based onendpart
andstartpart
. Under the described settings both are zero. Hence the following code performs a division by zero with floats. Assuming the compiler uses IEEE 745 this is fine and the result is infinity (if an exotic compiler doesn't support IEEE 745, this would already be undefined behavior).However, the result is later used to calculate
pnext
which is cast as integer and doing this with infinity as input is undefined behavior.The cause for
endpart
being zero is thattotparent
is zero inpsys_cache_child_paths()
([particle.c ]]). This value is assigned inpsys_thread_context_init_path()
([ https:*developer.blender.org/diffusion/B/browse/master/source/blender/blenkernel/intern/particle.c | particle.c ).Exact steps for others to reproduce the error
psys_tasks_create
afterparticles_per_task
is calculatedCreate a hair particle system and set the children to either Simple or Interpolated.
Depending on the circumstances, you may be able to detect undefined behavior when running Blender in a developer build on Linux with ASAN/UBSAN.
Added subscriber: @rjg
Changed status from 'Needs Triage' to: 'Confirmed'
This problem was originally discovered when investigating #83219.
Added subscribers: @sebbas, @JacquesLucke
@JacquesLucke @sebbas Since our current particle system implementation is EOL, I'm not sure how this should be handled. It seems that this might be a reason for some crashes with particle systems we've seen in the past.
Added subscriber: @end_ahmed
This issue was referenced by
357e519575
Changed status from 'Confirmed' to: 'Resolved'