BinExport assertion fail for register (unexpected child expression)

[mr-tz]

sample available on request

$ python scripts/inspect-binexport2.py tests/data/binexport2/sample.BinExport -d                                                                                                                                                                                             ─╯
DEBUG    inspect-binexport2: perf: loading BinExport2: 0.10s                                                                                                                                                                                                                                                               inspect-binexport2.py:31
DEBUG    inspect-binexport2: perf: indexing BinExport2: 1.56s                                                                                                                                                                                                                                                              inspect-binexport2.py:31
Traceback (most recent call last):
  File "capa/scripts/inspect-binexport2.py", line 461, in <module>
    sys.exit(main())
             ^^^^^^
  File "capa/scripts/inspect-binexport2.py", line 369, in main
    operands.append(render_operand(be2, operand, index=operand_index))
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "capa/scripts/inspect-binexport2.py", line 210, in render_operand
    _render_expression_tree(be2, operand, tree, 0, o)
  File "capa/scripts/inspect-binexport2.py", line 162, in _render_expression_tree
    raise NotImplementedError(len(children_tree_indexes))
NotImplementedError: 0

when passing that exception:

Traceback (most recent call last):
  File "capa/scripts/inspect-binexport2.py", line 462, in <module>
    sys.exit(main())
             ^^^^^^
  File "capa/scripts/inspect-binexport2.py", line 370, in main
    operands.append(render_operand(be2, operand, index=operand_index))
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "capa/scripts/inspect-binexport2.py", line 211, in render_operand
    _render_expression_tree(be2, operand, tree, 0, o)
  File "capa/scripts/inspect-binexport2.py", line 84, in _render_expression_tree
    assert len(children_tree_indexes) == 0
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AssertionError

on first triage I see a register with symbol z3 and child expression .

likely an issue in the BinExport plugin, which could be handled more gracefully here

[williballenthin]

would you send the be2 to me and i'll triage?

[williballenthin]

This is an aarch64 program. The exception occurs with the instruction at 0x53de58.

I think this isn't actually a real instruction (Ghidra is probably wrong here), but whatever, we should be able to handle whatever disassembly:

The BinExport2 indicates the operand looks like: z31.S, with structure like (z31 (. (S))):

or maybe its easier to understand, like:

reg: z31
     ^
     |
sym: .
     ^
     |
sym: S

Gemini tells me this isn't actually valid aarch64:

But again, we should be able to handle whatever disassembly the system produces, and we'd have to handle this case for the valid vector operands, anyways:

Today we assert that register operands have no children:

so we have to update this case to handle children, such as with aarch64 vector instructions.