LLDB ScriptedFrameProvider Failure On Arm32 Bots

Dec 3, 2025 by Alex Johnson 49 views

Introduction

This article addresses the failure of ScriptedFrameProviders in the LLDB debugger when running on arm32 bots. The issue was initially reported in the LLVM discussion forums, highlighting failures in tests related to scripted frame providers. Specifically, tests introduced as part of #170236 are failing on arm32 architecture bots. This article will delve into the details of the failure, analyze the error logs, and discuss potential causes and solutions.

Background on LLDB and ScriptedFrameProviders

Before diving into the specifics of the issue, it's important to understand the context. LLDB is the LLVM project's debugger, providing a powerful tool for debugging C, C++, and Objective-C programs. LLDB supports a variety of features, including the use of scripted frame providers. These providers allow developers to extend LLDB's functionality by using scripts to define custom stack frames. This is particularly useful in scenarios where the default frame unwinding mechanisms are insufficient, such as when dealing with custom calling conventions or heavily optimized code.

Scripted frame providers are a crucial feature for advanced debugging scenarios. They enable developers to inject custom logic into the frame unwinding process, allowing for more accurate and detailed stack traces. This is achieved by writing scripts (typically in Python) that define how to create and manage stack frames. When a debugger needs to display the call stack, it consults these providers to generate the frames. The flexibility offered by scripted frame providers makes them invaluable for debugging complex software systems.

The Problem: ScriptedFrameProvider Tests Failing on arm32

The core issue is that certain tests related to scripted frame providers are failing specifically on arm32 bots. The failures were observed in the LLVM buildbot infrastructure, which automatically builds and tests LLVM projects on various platforms. The error logs indicate that the tests test_circular_dependency_with_function_replacement and test_scripted_frame_objects are failing. These tests are part of the broader suite of tests for scripted frame providers and are designed to ensure that the feature works correctly under different conditions.

The initial report included a link to the buildbot logs, which provide detailed information about the failures. Analyzing these logs is crucial to understanding the root cause of the problem. The logs reveal that the tests are failing with AssertionError exceptions, indicating that the expected number of frames does not match the actual number of frames generated by the scripted provider. This suggests that the frame provider is either not being loaded correctly or is not functioning as expected on the arm32 architecture.

Analyzing the Error Logs

To further understand the problem, let's examine the specific error messages from the logs:

test_circular_dependency_with_function_replacement Failure:
```
AssertionError: 0 != 6 : Frame count should be unchanged (replacement, not addition)
```
This error occurs in the TestFrameProviderCircularDependency.py test file. The test is designed to verify a fix for circular dependencies in frame providers, specifically when the provider replaces function names. The assertion failure indicates that the frame count is not being correctly managed, suggesting an issue with how frames are being replaced or added in the context of a circular dependency.
test_scripted_frame_objects Failure:
```
AssertionError: 0 != 5 : Should have 5 custom scripted frames
```
This error occurs in the TestScriptedFrameProvider.py test file. The test aims to ensure that the provider can return ScriptedFrame objects correctly. The failure suggests that the expected number of custom scripted frames (5 in this case) is not being generated, indicating a problem with the provider's ability to create or return these objects.

Both error messages point to a discrepancy between the expected and actual number of frames. This could be due to various reasons, such as issues with the script loading mechanism, problems with the frame unwinding logic on arm32, or even subtle differences in the Python environment on the arm32 bots.

Potential Causes

Several factors could contribute to the failure of scripted frame providers on arm32 bots. Here are some potential causes:

Architecture-Specific Code: The scripted frame provider code might contain architecture-specific logic that is not correctly handling the arm32 architecture. This could be due to differences in register usage, stack layout, or calling conventions between arm32 and other architectures.
Python Environment Differences: The Python environment on the arm32 bots might differ from the environments used for other architectures. This could include differences in Python versions, installed modules, or environment variables. Such differences could affect the execution of the Python scripts used by the frame providers.
Loading Issues: The frame provider scripts might not be loading correctly on arm32. This could be due to file path issues, permission problems, or other environment-related factors.
Concurrency or Threading Issues: If the scripted frame provider code involves concurrency or threading, there might be race conditions or other synchronization problems that are more pronounced on arm32 due to its specific hardware characteristics.
Compiler Optimizations: Compiler optimizations specific to arm32 might be exposing bugs in the frame provider code that are not apparent on other architectures. This is less likely but still a possibility.
Bug in LLDB's arm32 Support: There might be a bug in LLDB's core functionality related to frame unwinding or stack frame management on arm32. This would be a more fundamental issue that would require deeper investigation into LLDB's internals.

Troubleshooting Steps

To diagnose and resolve the issue, a systematic approach is required. Here are some steps that can be taken:

Reproduce the Issue Locally: The first step is to try to reproduce the issue locally on an arm32 system or emulator. This allows for more controlled debugging and experimentation.
Add Debug Logging: Adding detailed logging to the scripted frame provider code can help pinpoint where the failures are occurring. This can involve logging function calls, variable values, and other relevant information.
Simplify the Test Cases: Reducing the complexity of the test cases can help isolate the specific conditions that trigger the failures. This might involve creating smaller, more focused tests that target specific aspects of the frame provider functionality.
Inspect the Stack Trace: Examining the stack trace of the failing tests can provide valuable clues about the sequence of events leading to the error. This can help identify the specific code paths that are problematic.
Use a Debugger: Using a debugger (such as LLDB itself) to step through the code can help understand the behavior of the frame provider and identify any unexpected execution patterns.
Compare with Other Architectures: Comparing the behavior of the frame provider on arm32 with its behavior on other architectures (such as x86-64) can highlight any architecture-specific issues.
Check Environment Variables and Paths: Ensuring that the environment variables and file paths are correctly set on the arm32 bots is crucial. This can help rule out issues related to script loading and resource access.

Potential Solutions

Based on the potential causes and the troubleshooting steps, here are some potential solutions:

Fix Architecture-Specific Code: If the issue is due to architecture-specific code, the code needs to be modified to correctly handle arm32. This might involve using conditional compilation or architecture-specific logic to adapt the code for arm32.
Address Python Environment Differences: If the Python environment is the problem, ensuring consistency across all platforms is essential. This might involve using virtual environments or specifying dependencies to ensure that the same Python version and modules are used everywhere.
Correct Loading Issues: If the scripts are not loading correctly, the file paths and permissions need to be checked. Additionally, any environment variables that affect script loading should be verified.
Resolve Concurrency Issues: If concurrency or threading is involved, ensuring proper synchronization and avoiding race conditions is crucial. This might involve using locks, mutexes, or other synchronization primitives.
Adjust Compiler Optimizations: If compiler optimizations are exposing bugs, reducing the optimization level or disabling specific optimizations might help. However, this is more of a workaround than a true solution, and the underlying issue should still be addressed.
Fix LLDB Bugs: If there is a bug in LLDB's arm32 support, it needs to be fixed in the LLDB codebase. This would involve identifying the bug, developing a patch, and submitting it for review.

Conclusion

The failure of ScriptedFrameProviders on arm32 bots is a significant issue that needs to be addressed to ensure the reliability of LLDB on this architecture. By systematically analyzing the error logs, considering potential causes, and implementing appropriate troubleshooting steps, the root cause of the problem can be identified and resolved. This article has provided a comprehensive overview of the issue, potential causes, and steps to take for diagnosis and resolution.

For more information on LLDB and its features, you can visit the official LLDB website.