segmentation fault in _default_material argument of create_structure_and_set_materials

[jianguan210]

When I ran a simulation case involved gradient calculation (calculate_gradient()), default_material in C++ implementation is never assigned the type of material_type and pointed to a valid memory allocation in the workflow of gradient calculation. So the conversion from void* to material_type is invalid. A simple workaround is to delete the "else if" branch, and It passed test cases. Please check this issue.

[stevengj]

A simple workaround is to delete the "else if" branch

Which else if branch?

[stevengj]

I'm not clear on what simulation you are running — IIRC, anything that calls the routines in meepgeom.cpp should normally call set_materials_from_geometry first, which initializes default_material?

[oskooi]

To provide some additional information, the error reported by the address sanitizer is related to the statement (material_data *)default_material which occurs in three places within meepgeom.cpp:

meep/src/meepgeom.cpp

Lines 402 to 406 in f2bae0c

	if (!tp && is_material_grid(default_material)) {
	map_lattice_coordinates(p.x,p.y,p.z);
	gradient = material_grid_grad(p, (material_data *)default_material);
	++matgrid_val_count;
	}

meep/src/meepgeom.cpp

Lines 444 to 448 in f2bae0c

	if (!tp && is_material_grid(default_material)) {
	map_lattice_coordinates(p.x,p.y,p.z);
	u = material_grid_val(p, (material_data *)default_material);
	if (matgrid_val_count == 0) udefault = u;
	if (u < umin) umin = u;

meep/src/meepgeom.cpp

Lines 2549 to 2553 in f2bae0c

	mg = (material_data *)tp->objects[oi].o->material;
	else if (!tp && ((material_type)default_material)->which_subclass == material_data::MATERIAL_GRID)
	mg = (material_data *)default_material;
	else
	return; /* no material grids at this point */

The issue here is that default_material is of type void * and in certain cases it is a NULL pointer (?) because its default value is nothing as defined in libctl:

(define nothing (if (eq? MATERIAL-TYPE 'SCM)
                   '()
                   (if (for-all? (class-properties-all material-type)
                                 property-has-default?)
                       (make material-type)
                       no-default)))

(define-input-var default-material nothing MATERIAL-TYPE)

A NULL pointer therefore cannot be cast into a material_data * which is where the error arises. Perhaps we should just check that default_material is not NULL as part of the assignment?

[stevengj]

It seems like there is a missing init_libctl call in _get_gradient? Also relevant to #1574.

[oskooi]

The problem here seems to be SWIG deleting the _default_material argument at the end of create_structure_and_set_materials. Inside this function, _default_material is passed to init_libctl which is then assigned to the global variable default_material:

meep/python/meep.i

Lines 1887 to 1889 in ef8f6fc

	bool _ensure_periodicity,
	meep_geom::material_type _default_material,
	meep_geom::absorber_list alist,

meep/python/meep.i

Lines 1907 to 1908 in ef8f6fc

	meep_geom::init_libctl(_default_material, _ensure_periodicity,
	&gv, cell_size, center, &gobj_list);

meep/src/meepgeom.cpp

Lines 2060 to 2070 in ef8f6fc

	void init_libctl(material_type default_mat, bool ensure_per, meep::grid_volume *gv,
	vector3 cell_size, vector3 cell_center,
	geometric_object_list *geom_) {
	geom_initialize();
	default_material = default_mat;
	ensure_periodicity = ensure_per;
	geometry_center = cell_center;
	dimensions = meep::number_of_directions(gv->dim);
	geometry_lattice.size = cell_size;
	geom_fix_object_list(*geom_);
	}

Note that _default_material is of type meep_geom::material_type which is a pointer to the struct material_data:

meep/src/material_data.hpp

Line 232 in ef8f6fc

typedef material_data *material_type;

The SWIG generated file meep-python.cxx shows that the _default_material argument of create_structure_and_set_materials (arg18) is being deleted as part of the function SWIGINTERN PyObject *_wrap_create_structure_and_set_materials(PyObject *SWIGUNUSEDPARM(self), PyObject *args):

    if (arg18) {
      if (arg18->medium.E_susceptibilities.items) {
        delete[] arg18->medium.E_susceptibilities.items;
      }
      if (arg18->medium.H_susceptibilities.items) {
	delete[] arg18->medium.H_susceptibilities.items;
      }
      delete[] arg18->weights;
      delete[] arg18->epsilon_data;
      delete arg18;
    }

The obvious solution seems to be to just prevent SWIG from deleting _default_material. Putting a const in front of this argument in the function header for create_structure_and_set_materials doesn't do this. Do we need to somehow explicitly tell SWIG not to delete _default_material?