[Missing definitions] Every non-aliased variable should be defined, but variable has no definition.

[NeoQuix]

What happened?

Error in bin/sacsess.exe in 0x140003750
[pipeline.py:107 run()] ERROR - Failed to decompile ?Write@CVTUTF8Scraper@@UEAAHXZ, error during stage insert-missing-definitions: Every non-aliased variable should be defined, but variable rdx_2#4 has no definition.
Traceback (most recent call last):
  File "/home/neoquix/Git-Repos/DeWolf/decompile.py", line 76, in <module>
    main(Decompiler)
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/util/commandline.py", line 80, in main
    task = decompiler.decompile(function_name, options)
  File "/home/neoquix/Git-Repos/DeWolf/decompile.py", line 51, in decompile
    pipeline.run(task)
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/pipeline/pipeline.py", line 109, in run
    raise e
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/pipeline/pipeline.py", line 102, in run
    instance.run(task)
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/pipeline/preprocessing/missing_definitions.py", line 99, in run
    self.insert_missing_definitions()
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/pipeline/preprocessing/missing_definitions.py", line 133, in insert_missing_definitions
    self._insert_definition_if_undefined(variable, previous_ssa_labels, undefined_variables)
  File "/home/neoquix/Git-Repos/DeWolf/decompiler/pipeline/preprocessing/missing_definitions.py", line 157, in _insert_definition_if_undefined
    raise ValueError(f"Every non-aliased variable should be defined, but variable {variable} has no definition.")
ValueError: Every non-aliased variable should be defined, but variable rdx_2#4 has no definition.

How to reproduce?

Decompile sacsess at 0x140003750.

Affected Binary Ninja Version(s)

3.3.3996

[ebehner]

The problem is that the phi-function for variable rdx_2#4 is missing. Having a look at the program in MLIL, one can see that rdx_2 is defined twice, and two different definitions can reach the usage in the "last" block:

Now, in MLIL SSA-form, Binary Ninja assign different SSA-labels for the two definitions and another one for the usage. However, the phi-function at the beginning of the block is missing. There is only the phi-function for rdx_3#4 = phi(rdx_2#2, rdx_2#3), but there should also be the phi-function rdx_2#4 = phi(rdx_2#2, rdx_2#3):

We have two options:

1. We say it is a Binary Ninja problem and ignore it or write an Issue
2. We update the missing definitions algorithm and introduce such phi-functions by our own.

[ebehner]

preferable, binary ninja issue
block issue until fixed by binary ninja, if they will not do it, we will try to solve it by our own.

[NeoQuix]

Will block for now and create a bninja issue later.

[NeoQuix]

Upstream: Vector35/binaryninja-api#4546