ZTEST Seg Faults On Native_sim When Providing Intuitive Yet Incorrect "-test=" Param.

Jun 15, 2025 by ADMIN 86 views

ZTEST Segmentation Fault on Native Simulation with Incorrect Test Parameter

Introduction

This article addresses a critical issue encountered while running tests using the ZTEST framework on the native_sim board. Specifically, a segmentation fault occurs when providing an intuitive but incorrect -test= parameter. This issue highlights the importance of clear and robust error handling in testing frameworks to prevent unexpected crashes and improve the user experience. In this comprehensive guide, we will delve into the details of the problem, its causes, and potential solutions. By understanding the intricacies of this issue, developers can avoid similar pitfalls and ensure the reliability of their testing processes.

Problem Description

When building tests for the native_sim board, a built ZTEST executable crashes when provided with an intuitive yet incorrect -test= parameter. The user defined a ZTEST_SUITE(TempTests, NULL, NULL, NULL, NULL, NULL); and ZTEST(TempTests, testTemp) in a C/C++ file. When the executable is run with the argument --test="TempTests":

west build -b native_sim
./build/test/zephyr/zephyr.exe --test="TempTests"

the executable crashes with a segmentation fault:

*** Booting nRF Connect SDK v3.0.1-9eb5615da66b ***
*** Using Zephyr OS v4.0.99-77f865b8f8d0 ***
Running TESTSUITE TempTests
===================================================================
Segmentation fault (core dumped)

Root Cause Analysis

The root cause of this issue lies in the incorrect syntax used to specify the test suite. While --test="TempTests" might seem intuitive, the correct syntax for running an entire suite is --test="TempTests::*". The segmentation fault occurs because the testing framework's argument parsing logic does not handle the incorrect syntax gracefully. Instead of providing a clear error message, it leads to a crash, making it difficult for users to understand the problem and find a solution.

By using GDB (GNU Debugger), the issue can be further investigated. Running the executable with GDB reveals the following call stack:

gdb --args ./build/test/zephyr/zephyr.exe --test="TempTests"
run
bt
Thread 3 "main" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xf70ffac0 (LWP 431681)]
0xf7bd61eb in ?? () from /lib32/libc.so.6
(gdb) bt
#0  0xf7bd61eb in ?? () from /lib32/libc.so.6
#1  0x0804cda2 in z_ztest_testargs_contains (suite_name=suite_name@entry=0x80553aa "TempTests", 
    test_name=test_name@entry=0x80553b4 "testTemp")
    at /home/gbmhunter/personal/zephyr-cpp-toolkit/external/zephyr/subsys/testsuite/ztest/src/ztest_posix.c:166
#2  0x0804ce22 in z_ztest_should_test_run (suite=0x80553aa "TempTests", test=0x80553b4 "testTemp")
    at /home/gbmhunter/personal/zephyr-cpp-toolkit/external/zephyr/subsys/testsuite/ztest/src/ztest_posix.c:193
#3  0x0804c6c3 in z_ztest_run_test_suite_ptr (
    suite=suite@entry=0x805c438 <z_ztest_test_node_TempTests>, case_iter=case_iter@entry=1, 
    param=param@entry=0x0, suite_iter=1, shuffle=<optimized out>)
    at /home/gbmhunter/personal/zephyr-cpp-toolkit/external/zephyr/subsys/testsuite/ztest/src/ztest.c:878

This call stack indicates that the segmentation fault occurs within the z_ztest_testargs_contains() function. This function is responsible for checking if the provided test argument matches the current test suite and test case. The crash likely results from incorrect string format assumptions within this function.

The Importance of User-Friendly Error Handling

Instead of a segmentation fault, the system should ideally return an informative error message when an incorrect -test= parameter is provided. This would guide the user to the correct syntax and prevent the frustration caused by an unexpected crash. Robust error handling is crucial for creating a positive user experience and ensuring that developers can quickly resolve issues during testing.

Detailed Analysis of the Segmentation Fault

Examining `z_ztest_testargs_contains()`

The z_ztest_testargs_contains() function is a critical part of the ZTEST framework, responsible for parsing and validating the test arguments provided by the user. When an incorrect argument is supplied, this function's behavior can lead to a segmentation fault if it doesn't properly handle the malformed input. The function likely makes certain assumptions about the format of the input string, and when these assumptions are violated, it results in memory access errors.

Memory Access Errors and Segmentation Faults

A segmentation fault is a specific type of error that occurs when a program attempts to access a memory location that it is not allowed to access. This can happen for various reasons, such as attempting to write to a read-only memory location, accessing memory that has not been allocated, or dereferencing a null pointer. In the context of the z_ztest_testargs_contains() function, the segmentation fault likely occurs due to an attempt to access an invalid memory address resulting from the incorrect parsing of the --test parameter.

Understanding the Correct Syntax

The correct syntax for specifying a test suite in ZTEST is --test="TestSuiteName::*", where TestSuiteName is the name of the test suite you want to run. The ::* part is essential because it tells ZTEST to run all test cases within that suite. When the user provides --test="TempTests", ZTEST does not recognize this as a valid suite specification and attempts to process it in a way that leads to a crash.

The Role of GDB in Debugging

GDB is an invaluable tool for debugging such issues. By running the program under GDB and examining the backtrace, developers can pinpoint the exact location in the code where the segmentation fault occurs. The backtrace provides a call stack, showing the sequence of function calls that led to the crash. This information is crucial for understanding the flow of execution and identifying the root cause of the problem. In this case, the GDB output clearly indicates that the issue originates within the z_ztest_testargs_contains() function.

Regression Analysis

Identifying the Regression

A regression analysis is essential to determine if the issue is a new problem or if it has existed in previous versions of the software. In this case, it is crucial to check if this behavior was present in earlier versions of the Zephyr OS and ZTEST framework. If the issue is a regression, it means that a recent change has introduced the bug, and identifying the specific change can help in resolving the problem more quickly.

Steps to Perform a Regression Analysis

Check Previous Versions: Test the same scenario on older versions of the Zephyr OS and ZTEST framework. This will help determine if the issue is new or has been present before.
Identify the Change: If the issue is a regression, try to identify the specific commit or change that introduced the bug. This can be done by bisecting the commit history or reviewing recent changes in the relevant code files.
Analyze the Code: Once the change is identified, carefully analyze the code to understand how it could have introduced the segmentation fault. Look for any modifications to the argument parsing logic or memory access patterns.

The Importance of Regression Testing

Regression testing is a critical part of software development. It ensures that new changes do not introduce bugs or break existing functionality. By performing regression tests regularly, developers can catch issues early and prevent them from making their way into production code.

Steps to Reproduce the Issue

Detailed Reproduction Steps

To reproduce the segmentation fault, follow these steps:

Set up the Environment: Ensure you have the necessary tools and environment set up for building and running Zephyr OS applications. This typically includes installing the Zephyr SDK and configuring your build environment.

Create a Test File: Create a C/C++ file with a ZTEST suite and a test case. For example:

#include <zephyr/ztest.h>
ZTEST_SUITE(TempTests, NULL, NULL, NULL, NULL, NULL);
ZTEST(TempTests, testTemp) {
zassert_true(true, "This test should pass");
}

Build the Executable: Use the west build command to build the executable for the native_sim board:
```
west build -b native_sim
```
Run the Executable: Run the executable with the incorrect -test parameter:
```
./build/test/zephyr/zephyr.exe --test="TempTests"
```
Observe the Crash: Observe the segmentation fault.

Importance of Clear Reproduction Steps

Providing clear and detailed steps to reproduce an issue is crucial for bug reporting and resolution. It allows developers to quickly verify the problem and start working on a fix. The more precise the steps, the easier it is for others to reproduce the issue and understand the context.

Relevant Log Output

Analyzing the Log Output

The log output from GDB provides valuable information for diagnosing the issue. The backtrace shows the function call stack at the time of the crash, which helps pinpoint the exact location in the code where the segmentation fault occurred. In this case, the log output clearly shows that the crash occurs within the z_ztest_testargs_contains() function.

Key Information in the Log Output

Signal Received: The log output indicates that the program received a SIGSEGV signal, which is the signal for a segmentation fault.
Crashing Function: The backtrace shows that the crash occurred within the z_ztest_testargs_contains() function.
Call Stack: The call stack provides the sequence of function calls that led to the crash, allowing developers to trace the flow of execution and understand the context of the error.

Using Log Output for Debugging

Log output is an essential tool for debugging software issues. By carefully analyzing the log output, developers can gain insights into the program's behavior and identify the root cause of problems. In the case of segmentation faults, the log output often provides crucial information about the memory access that triggered the error.

Impact of the Issue

Assessing the Impact

The impact of this issue is classified as "Annoyance – Minor irritation; no significant impact on usability or functionality." While the segmentation fault is a serious error, it only occurs when an incorrect -test parameter is provided. The correct syntax is known, and the issue can be easily avoided by using the correct syntax. However, the unexpected crash can be frustrating for users and may lead to confusion.

Potential for Escalation

While the current impact is minor, there is potential for escalation if the issue is not addressed. If the incorrect syntax is common or if the error handling is not improved, more users may encounter the problem, leading to increased frustration and potentially hindering the adoption of the ZTEST framework. Additionally, if the same error handling issue exists in other parts of the codebase, it could lead to more severe problems in the future.

Mitigation Strategies

To mitigate the impact of this issue, the following strategies can be employed:

Improve Error Handling: The most effective solution is to improve the error handling in the z_ztest_testargs_contains() function and provide a clear error message when an incorrect -test parameter is provided.
Update Documentation: Update the documentation to clearly explain the correct syntax for specifying test suites and test cases.
Provide Examples: Include examples of the correct syntax in the documentation and in tutorials to help users avoid this issue.

Environment Details

Specifying the Environment

The issue was encountered in the following environment:

OS: WSL, Ubuntu in Windows host
Zephyr Version: 77f865b8f8d0cb3d19002bfe713e9dd46e6f71b7 (HEAD, tag: v4.0.99-ncs1)

Importance of Environment Information

Providing detailed environment information is crucial for bug reporting and resolution. The environment can significantly impact the behavior of software, and knowing the OS, compiler version, and other relevant details can help developers reproduce the issue and identify the root cause. In this case, specifying the OS and Zephyr version allows others to replicate the environment and verify the problem.

Potential Environment-Specific Issues

It is possible that the segmentation fault is specific to certain environments. For example, it might only occur on WSL or on certain versions of Ubuntu. By providing the environment information, developers can investigate whether the issue is environment-specific and take appropriate action.

Additional Context

Providing Additional Information

In addition to the core details of the issue, it is often helpful to provide any additional context that might be relevant. This could include information about the use case, the specific goals of the testing, or any other observations that might help developers understand the problem.

The Value of Context

Context can be invaluable for bug resolution. It helps developers understand the bigger picture and make informed decisions about how to fix the issue. In some cases, the context might reveal that the issue is not a bug at all but rather a misunderstanding of how the software is intended to be used.

Examples of Additional Context

Use Case: Describe the specific scenario in which the issue was encountered. For example, "I was trying to run all tests in the TempTests suite as part of our nightly build process."
Goals: Explain the goals of the testing. For example, "We are testing the temperature sensor drivers and want to ensure that they are functioning correctly."
Observations: Share any other observations that might be relevant. For example, "I noticed that the issue only occurs when the -test parameter is enclosed in double quotes."

Conclusion

The segmentation fault encountered when providing an incorrect -test parameter to the ZTEST executable highlights the importance of robust error handling and clear communication in testing frameworks. While the current impact of this issue is minor, it underscores the need for user-friendly error messages and clear documentation. By addressing this issue, the ZTEST framework can provide a better experience for developers and ensure the reliability of testing processes. Improving error handling, updating documentation, and providing clear examples are key steps in mitigating the impact of this issue and preventing future occurrences.

Summary of Key Points

A segmentation fault occurs when providing an incorrect -test parameter to the ZTEST executable.
The correct syntax for specifying a test suite is --test="TestSuiteName::*".
The segmentation fault occurs within the z_ztest_testargs_contains() function.
The ideal solution is to improve error handling and provide a clear error message.
Updating documentation and providing examples can help users avoid this issue.

Next Steps

To resolve this issue, the following steps should be taken:

Implement Improved Error Handling: Modify the z_ztest_testargs_contains() function to provide a clear error message when an incorrect -test parameter is provided.
Update Documentation: Update the ZTEST documentation to clearly explain the correct syntax for specifying test suites and test cases.
Provide Examples: Include examples of the correct syntax in the documentation and in tutorials.
Test the Solution: Test the solution to ensure that the segmentation fault is resolved and that the error handling is functioning correctly.

By addressing this issue, the ZTEST framework can become more robust and user-friendly, helping developers ensure the quality and reliability of their software.