emit number(0) for insn like "xor eax, eax"

[v1bh475u]

closes #2622

Checklist

• No CHANGELOG update needed

• No new tests needed

• No documentation update needed

[gemini-code-assist]

Hello @v1bh475u, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

Summary of Changes

This pull request addresses issue #2622 and introduces a new feature to emit number(0) for instructions like xor eax, eax. This optimization helps in identifying and representing a common code pattern where a register is zeroed by XORing it with itself. The changes include modifications to capa/features/extractors/viv/insn.py to implement the feature and tests/fixtures.py to add a new test case. A changelog entry is also added.

Highlights

• New Feature: The pull request introduces a new feature to emit number(0) for instructions like xor eax, eax.
• Code Modification: The capa/features/extractors/viv/insn.py file is modified to implement the new feature.
• Test Case: A new test case is added to tests/fixtures.py to verify the new feature.

Changelog

• CHANGELOG.md
  • Added a new feature entry: emit number(0) for instructions like "xor eax,eax" emit number(0) (offset(0)??) for instructions like "XOR EAX, EAX" #2622 @v1bh475u
• capa/features/extractors/viv/insn.py
  • Added logic to detect xor eax, eax pattern and yield Number(0) feature at the instruction address (lines 597-607).
• tests/fixtures.py
  • Added a new test case for the xor eax, eax instruction pattern to verify the Number(0) feature extraction (line 1024).

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Trivia time!

What does XOR stand for in the context of bitwise operations?

Click here for the answer

XOR stands for exclusive OR.

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[gemini-code-assist]

Code Review

The pull request introduces a new feature to emit number(0) for instructions like "xor eax, eax", enhancing the detection capabilities of capa. The changes include modifications to the CHANGELOG, the core feature extraction logic, and the test suite. Overall, the changes seem well-structured and address the intended issue. However, there are a few areas that could benefit from further attention.

Summary of Findings

• Clarity of XOR Instruction Detection Logic: The logic for detecting the XOR instruction pattern could be made more explicit and potentially more robust by using constants for register names instead of directly comparing register objects. This would improve readability and maintainability.
• Test Coverage: While a new test case has been added, it might be beneficial to include additional test cases that cover different register combinations or edge cases to ensure the feature works as expected across various scenarios.

Merge Readiness

The pull request is almost ready for merging. Addressing the clarity of the XOR instruction detection logic and expanding the test coverage would further enhance the quality and reliability of the changes. I am unable to directly approve the pull request, and users should have others review and approve this code before merging. I recommend addressing the medium severity issues before merging.

[v1bh475u]

@williballenthin , I have tested binexport2 for arch64 but could not find any binary with arm architecture. However, I am confident that it will work. But let know me if there is any present in the database. We should add a test for that too.

[mr-tz]

I think we could emit these features from the 'extract_insn_nzxor_characteristic_features' functions to avoid duplicate code.

[v1bh475u]

I think we could emit these features from the 'extract_insn_nzxor_characteristic_features' functions to avoid duplicate code.

I think the extract_insn_nzxor_charateristic_features is its own particular route and we should try to emit these features from it. Instead, what we can do is abstract away their logic into new helper functions and use them in place of raw checking. Shall I change to that?

[mr-tz]

Interesting idea, can you show these changes for the vivisect extractor as an example?

Pro of the suggestion is a better separation, con is slightly more code.

[v1bh475u]

@mr-tz , can you please review the example implementation? If you approve this, I can do the same for other backends too.

[v1bh475u]

@mr-tz , can you please review the example implementation? If you approve this, I can do the same for other backends too.

@mr-tz ?

[v1bh475u]

Reason: The previous commit contained a logical bug, fixed in this commit.

[mr-tz]

Do you think we're fine without this helper here? The other ones are fine I think.

[v1bh475u]

Fair enough

[v1bh475u]

@williballenthin & @mr-tz , I have implemented the requested changes. Please review them whenever you are free.
Also, please run the tests for binary ninja backend and let know me if you run into any issue.

[v1bh475u]

@mr-tz @williballenthin, I've made the requested changes. Please review whenever you are free.

[mr-tz]

Can you ensure CI passes as well please?

[v1bh475u]

Done with the changes

[v1bh475u]

@mr-tz @williballenthin, can you please take a look at the changes that I have made whenever you are free and tell me if there is a need for further modifications?