[Bug] Bytecode Verification Failure When Storing A Function With An Unused Signer Param

Apr 25, 2025 by ADMIN 88 views

Introduction

In the world of smart contract development, bytecode verification is a crucial step in ensuring the integrity and security of our contracts. However, sometimes, even with the best intentions, we may encounter unexpected errors that can be frustrating to debug. In this article, we will delve into a specific bug that occurs when storing a function with an unused signer parameter, and explore the possible causes and solutions.

The Bug

Consider the following test code:

module 0xc0ffee::m {
    fun take(_x: u64) {}

    fun test(s: signer) {
        let f = |_s: signer| take(5);
        f(s);
    }
}

This code defines a module 0xc0ffee::m with two functions: take and test. The take function takes a u64 parameter, which is not used within the function. The test function takes a signer parameter s and creates a new function f that takes a signer parameter _s and calls the take function with the argument 5. Finally, the test function calls the f function with the s parameter.

However, when we try to compile this code, we encounter a bytecode verification failure with the error message:

bug: bytecode verification failed with unexpected status code `STLOC_TYPE_MISMATCH_ERROR`. This is a compiler bug, consider reporting it.
Error message: none
  ┌─ TEMPFILE:5:17
  │
5 │         let f = |_s: signer| take(5);
  │                 ^^^^^^^^^^^^^^^^^^^^

Understanding the Error

The error message indicates that there is a type mismatch error in the bytecode verification process. Specifically, the error occurs at line 5, where the let statement is used to create a new function f. The error message points to the signer type, which suggests that there is an issue with the type of the signer parameter.

Possible Causes

There are several possible causes for this error:

Type Mismatch: The most obvious cause is a type mismatch between the signer parameter and the u64 type used in the take function. However, this is not the case, as the signer parameter is not used within the take function.
Compiler Bug: The error message suggests that this is a compiler bug, which can be frustrating to debug. However, it is possible that the compiler is incorrectly handling the type of the signer parameter.
Unused Signer Param: The fact that the signer parameter is not used within the take function may be causing the compiler to incorrectly handle the type of the parameter.

Solutions

To resolve this issue, we can try the following solutions:

Remove Unused Signer Param: We can remove the unused signer parameter from the take function, as it is not used within the function.
Use a Different Type: We can use a different type for the take, such as u64, to avoid the type mismatch error.
Report Compiler Bug: If none of the above solutions work, we can report the compiler bug to the relevant authorities, as suggested by the error message.

Conclusion

In conclusion, the bytecode verification failure when storing a function with an unused signer param is a complex issue that requires careful analysis and debugging. By understanding the possible causes and solutions, we can resolve this issue and ensure the integrity and security of our smart contracts.

Additional Information

Compiler Version: The compiler version used to compile the code is not specified.
Platform: The platform used to compile the code is not specified.
Code: The code used to reproduce the issue is provided above.

Related Issues

Compiler Bug: The issue is related to a compiler bug, which can be reported to the relevant authorities.
Type Mismatch: The issue is related to a type mismatch error, which can be resolved by using a different type or removing the unused parameter.
Unused Signer Param: The issue is related to an unused signer parameter, which can be removed to resolve the issue.
Q&A: Bytecode Verification Failure When Storing a Function with an Unused Signer Param ====================================================================================

Introduction

In our previous article, we explored the issue of bytecode verification failure when storing a function with an unused signer param. In this article, we will provide a Q&A section to help you better understand the issue and its possible causes.

Q: What is bytecode verification failure?

A: Bytecode verification failure occurs when the compiler fails to verify the bytecode of a smart contract. This can happen due to various reasons, including type mismatch errors, compiler bugs, and more.

Q: What is the cause of this issue?

A: The cause of this issue is a type mismatch error between the signer parameter and the u64 type used in the take function. However, this is not the case, as the signer parameter is not used within the take function.

Q: Why is the compiler failing to verify the bytecode?

A: The compiler is failing to verify the bytecode because it is incorrectly handling the type of the signer parameter. This can be due to a compiler bug or a misunderstanding of the type system.

Q: How can I resolve this issue?

A: To resolve this issue, you can try the following solutions:

Remove Unused Signer Param: Remove the unused signer parameter from the take function, as it is not used within the function.
Use a Different Type: Use a different type for the take, such as u64, to avoid the type mismatch error.
Report Compiler Bug: If none of the above solutions work, report the compiler bug to the relevant authorities.

Q: What are the possible causes of this issue?

A: The possible causes of this issue are:

Type Mismatch: The most obvious cause is a type mismatch between the signer parameter and the u64 type used in the take function.
Compiler Bug: The error message suggests that this is a compiler bug, which can be frustrating to debug.
Unused Signer Param: The fact that the signer parameter is not used within the take function may be causing the compiler to incorrectly handle the type of the parameter.

Q: How can I prevent this issue in the future?

A: To prevent this issue in the future, you can follow these best practices:

Use clear and concise code: Avoid using complex code structures that can lead to type mismatch errors.
Use type annotations: Use type annotations to clearly define the types of your variables and function parameters.
Test your code thoroughly: Test your code thoroughly to catch any type mismatch errors before they become a problem.

Q: What are the implications of this issue?

A: The implications of this issue are:

Security risks: If left unchecked, this issue can lead to security risks, such as unauthorized access to sensitive data.
Performance issues: This issue can also lead to performance issues, such as slow execution times and increased memory.
Debugging challenges: This issue can make debugging more challenging, as it can be difficult to identify the root cause of the problem.